Using multimedia techniques in your programs allows you to be very creative. You can easily create flashy programs with sound and graphic effects. Applications that use multimedia elements are becoming more and more common as the processor speeds and disk capacities of PCs continue to reach new levels.
When you use the term multimedia, most people probably think of movies played on the computer with an accompanying soundtrack, or of graphics-intensive, interactive computer games. Some people might even think of the virtual reality simulations that are becoming more prevalent. While these are all uses of multimedia applications, multimedia itself has a much simpler definition. Multimedia is the use of different visual and audio techniques to present information or entertainment to the user. These techniques can include various types of audio material, animation, video, simple graphics, and even text. To give you a better understanding of multimedia as a whole, take a look at each of the elements of multimedia: sight, sound, and animation. A multimedia application combines these elements to provide an innovative and interesting user interface. Within each of the three broad categories are several elements. The discussion of these elements is the subject of this section.
Sound is probably the most familiar of all the multimedia elements. One simple example of working with sound is the humble beep. You often encounter a beep when you hit the end of a data entry field or try to click a window while a modal dialog box is being shown. While you would probably realize that you could not enter any more characters or move to another window after the computer refuses to respond to your request, the beep has become a way of notifying you that you have tried to perform an operation that is not allowed. This illustrates the way that sound is used in many applications, as a way to draw attention to the computer and to the task at hand.
As you might know, you can also configure your computer to play different sounds when different tasks are performed in Windows, and in response to different Windows messages. While the use of sounds in this manner is definitely not essential, the aural cues provide notification to the user even if he or she is not looking at the monitor. In addition, if you have a CD-ROM drive, most computers allow you to play music CDs by using a CD Player application like the one shown in Figure B3.1.
FIG. B3.1
Graphical interfaces to multimedia devices are provided by Windows 95's CD
Player and a sound card mixer.
A CD Player application mimics what a real CD player looks like. When you use the software, you are actually controlling a real-world device--your CD-ROM drive. This metaphor is extended to your sound card, which has several devices used to produce various sound effects. These devices are usually manipulated in a mixer application (also shown in Figure B3.1) that comes with your sound card.
The sound that you can typically use with your computer is divided into three key types: MIDI sound effects, WaveForm sounds, and CD Audio. Let's take a closer look at these three types of sound, each of which is controllable from Visual Basic.
MIDI MIDI is the abbreviation for Musical Instrument Digital Interface. MIDI provides a way to store the notes of an instrument (or instruments) in a digital format. The MIDI file actually contains instructions for use by an internal or external sequencer. The sequencer interprets the instructions and synthesizes the notes that are contained in the file. Typically, MIDI files are played through the sound card of your computer and output through the speakers. However, with the proper equipment, MIDI also provides you with a way to control instruments, such as electronic keyboards, and to accept input from MIDI instruments for storage.
NOTE: The sound quality of MIDI files depends on the sound card or device on which they are played. Some sound cards use a table of digitally sampled instruments, whereas others use a cruder sounding FM synthesizer. Keep this in mind when distributing a MIDI file.
The audio files for MIDI sounds are much smaller than similar files for WaveForm audio. This is because the MIDI file only contains instructions on how to create the note as opposed to actual sound samples. (This is similar to the differences between bitmap and raster graphics.) MIDI files are great for providing musical backgrounds for an application or Web page. The disadvantage of MIDI files is that you cannot use them for storing voice information, such as narrations or voice annotations, because they only simulate musical instruments.
WaveForm Audio WaveForm audio is digitized sound that has been stored in files on your computer. Because WaveForm audio is a sample of the actual sounds, it can contain music, voice, or a variety of other sound effects. WaveForm audio is one of the most common forms of audio used in a computer and one of the easiest to create. While MIDI files typically require specialized instruments to create the music, you can create WaveForm audio with a sound card and a microphone. Most sound cards that you get for your computer have the capability of accepting audio input for storage in WaveForm files. This input can come from a microphone, tape deck, or other audio source. To record WaveForm audio, you can use the Sound Recorder program that comes with Windows 95 (shown in Figure B3.2), or a sound recorder that comes with your sound card. These programs work in the same manner as a tape recorder or VCR.
To record sounds, just press the record button and start sampling the sounds you want to record. When you are finished recording, press the stop button and specify the file name and where you want to store the sounds. WaveForm audio provides an easy way to add narration to a program. You can also store tracks from an audio CD in Wave format before writing them to CD-R (recordable) media. WaveForm files, which usually have the extension WAV, are generally much larger than MIDI files. They can be recorded at a number of different sampling rates, which range from AM-radio to CD-sound quality.
FIG. B3.2
The Windows 95 Sound Recorder and other typical sound recorder programs let
you record audio for use in your programs.
CD Audio CD audio is the type of audio that you are used to hearing from your home or car stereo. The CD audio capabilities of your computer enable you to play music CDs on your computer. If you do not have a sound card, most CD drives have a headphone jack that lets you listen to the music while the CD Player program controls functions such as Play, Pause, and Skip. If you have a sound card, you can connect the CD to the sound card and play the music through the same speakers that are used for WaveForm files. CD audio gives you the highest sound quality of any of the audio types. However, it is different from a WAV file in that it is stored on an actual physical CD. You can use VB to play CD tracks in your program. This might be useful in creating a multimedia-enhanced CD-ROM, where you could store both the program and audio tracks on the same CD-ROM. In the past few years, CD-R drives and media have fallen in price, so creating your own CD-ROMS is well within reach. Typically, 176 kilobytes of storage are required for each second of CD audio. This allows about 73 minutes of audio (or 650 megabytes of data) to be stored on a single CD-ROM.
Determining What Your System Will Support For your computer to work with any of the types of sounds listed in the previous sections, you need to verify that your computer supports the sound type. The easiest way to determine what sounds your system supports is to use the Windows Media Player application (choose Start, Programs, Accessories, Multimedia, Media Player). After starting the Media Player, click the Device menu. This shows you what types of audio and video devices can be used on your computer (see Figure B3.3).
FIG. B3.3
The Windows 95 Media player (MPLAYER.EXE) lists the multimedia devices installed
on your system.
The three sound types discussed earlier in this section are represented by the following menu items in the Device menu:
As there were several different types of sound that you could use in your applications, there are also several types of visual elements that can be created or used in your Visual Basic pro-grams. These elements are digital and analog video, animation, and graphics, which includes still pictures, bitmaps, and charts. Which of these elements you use and how you use them depends on the nature of your application. Each element has different capabilities and uses in an application. Let's take a closer look at the major visual elements.
Video There are two types of video that can be used in your programs: video stored in files and video stored outside your PC. Video files are movies that have been captured by using a video capture board or digital camera and stored in a file on your computer. For motion video, a specified number of frames of information are stored per second of video. Typically, you have from 15 frames per second (fps) to 30 fps, which is considered full motion video. Digital video is the type that you find in most encyclopedia programs or tutorial disks that include video tracks. Some typical video file extensions are AVI, MPEG, and MOV. Video can also be received from an external device such as a laser disc, camera, or video cassette recorder (VCR). In this case, the computer program might be controlling the device or displaying it on the computer screen. Because of the need for specific external devices, this type of video is more difficult to use and distribute in your programs.
Animation Animation is simply displaying a series of images to give the user the impression of motion. You have probably seen animation used in Internet Explorer, where the globe spins while you are waiting for a page to load. You might have also seen animation in the Windows Explorer when you are copying a group of files. In this case, letters flying from one folder to another indicate that an operation is occurring (see Figure B3.4).
FIG. B3.4
File operations use animation to indicate an ongoing process.
There are two basic types of animation: frame-based animation and object-based animation. Frame-based animation uses a series of frames (usually bitmaps) displayed in rapid succession to give the illusion of motion. Each frame of the animation is a unique picture that displays the entire scene of the animation. Motion is achieved by making subtle changes in the position of objects in each frame of the animation. If you have ever created a flip-book cartoon, you have used frame-based animation. Many animated cartoons use frame-based animation.
In object-based animation, each object of a scene is independent from the others. In object-based animation, an authoring program is used to change the relative placement of each object from scene to scene. This technique is also known as sprite animation. An example would be using a timer control to increment the Left property of a PictureBox, thus making it "move" across the screen.
Graphics Graphics are static images, in contrast to video or animation. However, graphics comprise a large portion of many multimedia applications. Graphics can include still pictures, bitmap illustrations, business charts, and even dynamic charts that change over time. (For more information about using graphics in your programs, see Chapter 12, "Working with Graphics.")
The final piece of the multimedia puzzle is text. Although text is not as glamorous as video or sound, it is a very important part of almost any program you create. Text still provides you with the most efficient way to present a large amount of information. Text also takes up less space than other media and is easier to use as reference material. Even though text is not fancy, this does not mean that it has to be boring. You can use fonts and color to liven up your text and highlight key information. You can also use specialized text files, like HTML, along with a browser to implement jumps between one document and another. This makes your text interactive to the user. Chapter 14, "Working with Text, Fonts, and Colors,"covers this in more detail.
As you have seen, there are a number of elements that can be involved in a multimedia program. Likewise, there are a number of uses for multimedia applications. Some of these uses include:
As you begin programming multimedia applications, you will probably find more uses for them than you could have imagined.
Animation is one of the easiest multimedia effects to add to your applications. As you read earlier, animation is simply presenting a series of images in succession. You can use animation to simulate motion of an object, to indicate time passing, or to add transition effect for elements of a presentation. Many parts of the Windows operating system use animation to let the user know that a program is performing a task, such as copying a file or loading a program. Animation is also used in most screen savers to provide a little entertainment. (Some screen savers take this to the extreme by providing a series of animated cartoons. Some of these are so much fun to watch that you forget about doing other work.)
Within Visual Basic, there are two basic ways to handle animation. First, you can write code to present the image series yourself. This method provides you with the most flexibility because you control the images being shown, the timing of the images, and all other aspects of the animation. The second method for adding animation to your program is to use the Animation control.
NOTE: You can also provide some very simple animation for toolbars and command buttons by changing pictures on the buttons as they are pressed. One example is to open a door on the exit button as it is clicked by the user.
To create your own animations, you need three things:
To illustrate the concepts involved in creating animation, let's walk through the process of creating a simple animation program that creates a rotating moon on the form.
The source code and bitmaps for this project are located on the companion CD-ROM.
Setting Up the Basic Form The first step to creating an animation sequence is to set up the basic form for displaying the images of the sequence. The form needs a control to show the images, command buttons to start and stop the animation sequence, and a text box to allow the user to enter the speed of the animation. To create the basic form, follow these steps:
When you have finished these six steps, your form should look like the one in Figure B3.5.
FIG. B3.5
The basic form provides control functions for the animation.
Setting Up the Image Source The next step in creating the animation program is to set up the source of the images for the series. For the demonstration, you use an array of image controls. This array is named imgSource and consists of eight image controls with the Index properties ranging from 0 to 7. After you have created the control array, you need to set the picture property of each of the controls. In our example, there are eight bitmaps that display a moon in various phases. These images can be created in the Windows Paint program fairly easily. After setting the Picture property of the Image controls to a different bitmap, you need to set the Visible property of the controls of the array to False. This keeps the source images from being displayed when the program is run. When you have finished setting up the source images, your form will look like the one in Figure B3.6.
FIG. B3.6
A control array holds the source images.
NOTE: You could also use an ImageList control to store the images for the animation sequence.
Handling the Changing of Images The final step to creating the animation program is to set up the code to show the images in sequence. This involves setting the initial picture of the sequence and displaying subsequent pictures at a specified time interval. The first thing you need to do in the code is to set up module level variables to determine the interval for changing images, the current image sequence number, and a flag to determine whether the animation is running or stopped. These variables are declared in the Declarations section of the frmAnimate form. The declarations are shown in Listing B3.1.
Dim PicNum As Integer, RunAnimate As Boolean Dim RotInterval As Single Private Sub Form_Load() imgAnimate.Picture = imgSource(0).Picture PicNum = 0 End Sub
After the variables are declared, the Load event of the form initializes the variables and places the first image of the sequence in the image control used for display. This is also shown in Listing B3.1.
Next, you need to write the code for the two command buttons that start and stop the animation. In the Click event for the cmdStart button, you retrieve the time interval between image changes from the text box and then set the run flag to indicate that the animation is running. Finally, you call the routine that actually runs the animation. The cmdStop button performs a single function: it sets the RunAnimate flag to False to terminate the animation run. The code for these two command buttons is shown in Listing B3.2.
Private Sub Command1_Click() RotInterval = Val(txtSpeed.Text) RunAnimate = True RotateMoon End Sub Private Sub Command2_Click() RunAnimate = False End Sub
The final routine is the one that changes the image displayed to the next one in the sequence. The code for this routine is shown in Listing B3.3.
Private Sub RotateMoon()
Dim StTime As Single, CurTime As Single
Do While RunAnimate
imgAnimate.Picture = imgSource(PicNum).Picture
DoEvents
StTime = Timer
Do
CurTime = Timer
Loop Until CurTime > StTime + RotInterval
PicNum = PicNum + 1
If PicNum > 7 Then PicNum = 0
Loop
End Sub
As you can see in Listing B3.3, the code runs as long as the variable RunAnimate is set to True. With each pass through the loop, the Picture property of the imgAnimate control is set to the Picture property of one of the source image controls. The index of the control is determined by the PicNum variable. This variable gets incremented each time you pass through the loop. Because the Index property of the control array only ranges from 0 to 7, the PicNum variable gets reset to 0 each time it goes past 7. This causes the sequence to start over and avoids any errors associated with an index out of range. The interior loop is the one that delays the execution of the next pass of the loop until the specified interval has passed. Timer is a VB function that returns the number of seconds that have elapsed since midnight. The returned value is a Single data type and can handle fractional seconds. The inner loop repeatedly calls the Timer function until the interval has elapsed.
One final line of note is the DoEvents statement. This statement serves two purposes. First, it gives your program a chance to update the image so the new picture is displayed. Without this, you would see a single image displayed on the form. The second purpose is to allow the user to click the Stop button to terminate the animation.
NOTE: Instead of using the Timer function, you could place the code to change the images in the Timer event of a Timer control. You would then set the Interval property of the timer control to the value specified by the text box.
Running the Program After saving your program, press F5 or click the Start button to run the program. Set a value for the image interval and click the Start button. If you leave the interval set at 1 second, you see the images change in a discrete manner. If you set the interval to 0.1 seconds, the image changes quickly enough that the rotation of the moon appears to be continuous. Try several settings of the interval and see how it affects the behavior of the animation.
NOTE: Because of executing the DoEvents statement, continuing to reduce the interval beyond a certain point produces no appreciable speed increase. For the test machine I was using, this interval was 0.05 seconds. If you require extremely fast graphics, you might want to look into using a graphics API, such as DirectX.
The other method of displaying animation sequences in your programs is to use the Animation control. This control displays silent digital video files (.AVI). The control allows you to start and stop the animation process as well as determine whether the animation sequence stops at the end of the file or loops back to repeat the sequence. AVI files can be created by using a video capture card with a video camera or VCR.
In the previous sections, you learned about what multimedia is and what types of elements can be used in a multimedia application. You also learned a little bit about creating your own animation effects with code. Although the animation is important, the bulk of your multimedia work will involve accessing different types of multimedia files and playing them through the various multimedia devices on your system. For this, you need a method to open the files, access the appropriate device, and then play the files. In most cases, you also need a method to control the playback of information. For example, most people would not be too happy with a CD player that played all tracks straight through. Your users will want the ability to skip tracks, replay certain tracks, and pause the playback. All these things can be handled with your multimedia programs.
In Windows, multimedia devices are handled through the Media Control Interface (MCI). MCI is a set of Windows functions that can be used to control all aspects of working with multimedia files, from setting up the devices, to pausing playback, to providing information about the current position within the playback (for example, elapsed time). These functions can be accessed directly by declaring the appropriate functions in your Visual Basic program and making the proper function calls to handle your needs. Using the API functions provides you with the most flexibility in programming multimedia applications.
NOTE: The API functions used to control multimedia devices are not covered extensively in this book. However, there are some examples of this in Chapter 35, "Accessing the Windows 32 API."
Fortunately, Microsoft has also provided you with an easier way to handle controlling multimedia devices. The Multimedia control (MCI32.OCX) provides you with easy access to most of the functions of the API. The control does this through properties that can be set at design time and changed at runtime. The Multimedia control also uses events to notify you of things taking place in your program, such as the end of playback. Using the Multimedia control will handle a large portion of your multimedia programming needs.
The first step to working with the Multimedia control is to add it to your toolbox. You do this by choosing the Components item from the Project menu, checking the box next to the Microsoft Multimedia Control 5.0 item, and then clicking OK. The next step is to add the control to your form. You do this by clicking the control in the Toolbox and drawing it on the form just like any other control. Figure B3.7 shows a form with two Multimedia controls.
Fig. B3.7
The Multimedia control first appears in a horizontal orientation, but you
can change it to vertical with the control's Orientation property.
There are two properties that control the basic appearance of the control. The Orientation property determines whether the control is drawn horizontally or vertically. The BorderStyle property determines whether a single line border is drawn around the buttons of the control.
As you can see in Figure B3.7, all the buttons of the control are displayed when you draw the control and all the buttons are shown as disabled. When you run a program with the Multimedia control, it automatically enables the buttons that are applicable for the type of media you are accessing. As you examine using the Multimedia control to access different types of multimedia elements, you will see which buttons are enabled for each element. For now, let's look at what each button does:
NOTE: Buttons on the control are handled automatically only if the AutoEnable property is set to True (its default setting). If you set the AutoEnable property to False, your program has to handle enabling and disabling the appropriate buttons in the control.
By default, all of the buttons are shown while the Multimedia control is in use and only the appropriate buttons are enabled. If you want to manually enable and disable buttons, or hide the buttons that are not in use, you can do so through the Enabled and Visible properties of each button. These properties are set to either True or False and work just like the Enabled and Visible properties of a regular control. Table B3.1 lists the property names for the different buttons.
| Button Name | Enable Property | Visible Property |
| Previous | PrevEnabled | PrevVisible |
| Next | NextEnabled | NextVisible |
| Play | PlayEnabled | PlayVisible |
| Pause | PauseEnabled | PauseVisible |
| Back | BackEnabled | BackVisible |
| Step | StepEnabled | StepVisible |
| Stop | StopEnabled | StopVisible |
| Record | RecordEnabled | RecordVisible |
| Eject | EjectEnabled | EjectVisible |
After you have drawn the Multimedia control on your form, you are ready to start working with multimedia devices. To work with any multimedia device, you need to set the DeviceType property of the control. You can set this property at design time or at runtime. The DeviceType property tells the control the type of information that it will be processing, such as a WAV file or CD Audio. Then, depending on the type of device that you are using, you might also need to specify the FileName property. For the devices that use files, the FileName property specifies the file to use for playback or recording. As with the DeviceType property, you can set the FileName property either at design time or runtime. Typically, your applications will include the capability to set the FileName at runtime so that multiple files can be played. Table B3.2 provides a list of the DeviceType settings for the Multimedia control and tells you whether a FileName is required for the device.
| Device | DeviceType Setting | FileName Required |
| AVI videos | AVIVideo | Yes |
| Music CDs | CDAudio | No |
| Digital Audio Tape | DAT | No |
| MIDI | Sequencer | Yes |
| Wave sounds | WaveAudio | Yes |
Setting the DeviceType and FileName properties are the only parts of the Multimedia control setup that can be done in the design environment. To complete the setup of the control, you must open the device and file that you want to use. This function, as well as control of the recording or playback, can be accomplished only by using code while your program is running. You control the multimedia devices through the use of the Command property of the Multimedia control. To open a device for use, you need to set the Command property, as shown in the following line of code:
mmcAudio.Command = "Open"
After this command is issued, the device is opened and the appropriate buttons of the Multimedia control are enabled (assuming you left the AutoEnable property set to True). If you want to use just the Multimedia control for playing sounds and movies, the Open command is the only one that you need to use. The control itself handles running the other commands necessary to play or otherwise control the multimedia device. If you want to use your own buttons or other code to control the multimedia device, you need to use other settings of the Command property. Table B3.3 lists the settings of the Command property and the corresponding button of the Multimedia control.
| Command | Button |
| Open | N/A |
| Close | N/A |
| Play | Play |
| Pause | Pause |
| Stop | Stop |
| Back | Back |
| Step | Step |
| Prev | Prev |
| Next | Next |
| Seek | N/A |
| Record | Record |
| Eject | Eject |
| Sound | N/A |
| Save | N/A |
In addition to the property settings of the Multimedia control, it has several events that you will utilize in creating your programs. These events are in addition to the standard events that are applicable to most controls. Let's start the discussion with the button events.
Button Events For each button of the Multimedia control, there are four events: Click, Completed, GotFocus, and LostFocus. These events are identified by the button name and the event name--for example, PlayClick for the Click event of the Play button. The GotFocus and LostFocus events for each button work just like the similar events for any other control. Therefore, focus on the Click and Completed events. The Click event of each button automatically invokes the command associated with the button. For example, when you click the Play button, play of the device automatically starts; you do not have to write code to make it happen. Therefore, you use the Click event to handle any other tasks that are required when the button is pressed. One other difference between the Click event of the buttons and that of any other control is the Cancel parameter that is passed to the event. By setting this parameter to True, you prevent the button from performing its default command.
NOTE: The default command of a button is performed after all the other code in the Click event.
The Completed event of a button occurs when the MCI command issued by the button has finished. This allows you to write code to perform a task at the end of a command. The Completed event also passes an Errorcode parameter. This parameter tells you whether the command completed successfully. If so, the Errorcode parameter is 0; otherwise, the Errorcode is set to a value that indicates the problem that occurred.
Other Events In addition to the button events, there are two other key events for the Multimedia control: the Done event and the StatusUpdate event. The Done event does for the control as a whole what the Completed event does for a button. The Done event is fired when a command has completed. The Done event passes the NotifyCode parameter to tell you the completion status of the command. The values of the NotifyCode parameter are shown in Table B3.4.
| Value | Description |
| 1 | The command completed successfully. |
| 2 | The command was stopped and superseded by another command. |
| 4 | The command was aborted by the user. |
| 8 | The command failed. |
The StatusUpdate event occurs automatically at specified intervals. This event updates the properties of the Multimedia control that will inform you of the status of the multimedia device. For example, when playing a CD, the Multimedia control keeps track of which CD track is being played and how much of the CD has been played. This information is updated when the StatusUpdate event is fired. You can use the event to display this information in your program. The interval used to fire the StatusUpdate is controlled by the UpdateInterval property. This property sets the number of milliseconds between events. The default value is 1000 milliseconds, which causes the StatusUpdate event to be fired once every second.
The best way to demonstrate the capabilities of the Multimedia control is to write some sample programs that use the control and its commands. This section shows you the basics of creating applications to play CD Audio, AVI videos, MIDI files, and WaveForm sounds. In each section, you see how to set up the control and how to get status information from the control. You also see which buttons of the control are enabled for each type of multimedia element.
The first multimedia element you will work with is CD Audio. Because the CD Audio does not require a file name, it is quite easy to set up. You only have to specify the DeviceType for the Multimedia control and issue the Open command to open the device. The control takes care of the rest of the task. When there is an Audio CD in your CD drive, the following buttons of the Multimedia control are enabled:
NOTE: The Pause and Stop buttons are only enabled while the CD is playing, and the Play button is only enabled while the CD is stopped.
The sample project for this section is located on the companion CD-ROM as CDPLAYER.
Setting Up the Basic Program To begin creating a CD player with the Multimedia control, you need to start a new project and then follow these steps:
mmcCDPlayer.Command = "Open"
When you have completed these steps, your form should look like the one in Figure B3.8.
FIG. B3.8
A simple CD Player can easily be created with the Multimedia control.
To play a CD, run the program. If you already have an audio CD in the drive, the Play button of the Multimedia control will be enabled and you can start the playback. If there is a data disk or no disk in the drive, only the Eject button will be enabled. The control keeps polling the CD drive to determine when it contains an audio CD. As soon as you place an audio CD in the drive, the appropriate buttons will be enabled.
Determining the Track Number and Total Tracks While you can now play CDs with your program, the program is not very informative to the user. There is no information about the number of tracks on the CD or which track is being played. You can remedy this situation with a couple of additional controls and a little bit of code. You first need to add controls to keep up with the number of tracks and the current track. You can do this with labels, text boxes, or with a slider control. For the sample project, labels were used. You need to add four Label controls to your form--two to identify the information and two to hold the actual information. The sample application uses two control arrays--lblCDPlayer and lblTracks--to identify and hold the information, respectively. The updated form is shown in Figure B3.9.
FIG. B3.9
Keep up with the currently playing track of a CD.
To handle placing the information in the labels, you need to add code to the StatusUpdate event of the Multimedia control. The code accesses the Track and Tracks properties of the control. The Track property tells you the current track that is playing, and the Tracks property tells you the total number of tracks on the CD. The following code handles displaying the current track and total tracks:
lblTracks(0).Caption = mmcCDPlayer.Track lblTracks(1).Caption = mmcCDPlayer.Tracks
Determining Track Times In addition to determining the track information, you probably want your program to show the length of the current track and of the CD. You also probably want to show the elapsed time on the CD and the elapsed or remaining time for the track. Displaying this information is also handled by using code in the StatusUpdate event to access properties of the Multimedia control. To handle time information, there are four properties that you need to access:
Each of these properties return a time value based on the format specified in the TimeFormat property of the Multimedia control. Although there are a variety of formats that can be used, the simplest time format to work with returns the time values in milliseconds. You need to specify this format by setting the TimeFormat property to 0 in the Load event of your form. You also need a routine that converts the times to an hours:minutes:seconds format to display to the users. This function is shown in Listing B3.4.
NOTE: Not all TimeFormat settings are supported by all multimedia devices.
Private Function ConvTime(ByVal TimeIn As Long) As String
Dim ConvHrs As Integer, ConvMns As Integer, ConvSec As Integer
Dim RemTime As Long, RetTime As String
RemTime = TimeIn / 1000
ConvHrs = Int(RemTime / 3600)
RemTime = RemTime Mod 3600
ConvMns = Int(RemTime / 60)
RemTime = RemTime Mod 60
ConvSec = RemTime
If ConvHrs > 0 Then
RetTime = Trim(Str(ConvHrs)) & ":" Else
RetTime = "" End If
If ConvMns >= 10 Then
RetTime = RetTime & Trim(Str(ConvMns))
ElseIf ConvMns > 0 Then
RetTime = RetTime & "0" & Trim(Str(ConvMns))
Else
RetTime = RetTime & "00" End If
RetTime = RetTime & ":" If ConvSec >= 10 Then
RetTime = RetTime & Trim(Str(ConvSec))
ElseIf ConvSec > 0 Then
RetTime = RetTime & "0" & Trim(Str(ConvSec))
Else
RetTime = RetTime & "00" End If
ConvTime = RetTime
End Function
To display the desired times, you need to add a few more Label controls to your form. You need four more controls to identify the numbers and then two controls for the track times and two for the CD times. The final appearance of the form is shown in Figure B3.10.
FIG. B3.10
CD Player with track times shown.
Retrieving the track length, CD length, and CD position are quite easy; you simply retrieve the values of the TrackLength, Length, and Position properties respectively and convert the values to the desired time format. To get the position within the track, you have to subtract the starting position of the track (specified by the TrackPosition property) from the current CD position (Position property). This value is then converted to the appropriate time format. All of this code is placed in the StatusUpdate event so that the information gets updated on a regular basis. Listing B3.5 shows the final code for the StatusUpdate event.
Private Sub mmcCDPlayer_StatusUpdate() lblTracks(0).Caption = mmcCDPlayer.Track lblTracks(1).Caption = mmcCDPlayer.Tracks lblTrackTime(0).Caption = ConvTime(mmcCDPlayer.TrackLength) lblTrackTime(1).Caption = ConvTime(mmcCDPlayer.Position_ - mmcCDPlayer.TrackPosition) lblCDTime(0).Caption = ConvTime(mmcCDPlayer.Length) lblCDTime(1).Caption = ConvTime(mmcCDPlayer.Position) End Sub
The Multimedia control also makes it easy for you to run AVI movies from your applications. These movies are stored in AVI files on your computer. The basic setup for running movies is very similar to that which was used for setting up the CD application. The only additional setup required is that the name of a file containing an AVI clip must be entered into the FileName property. After a valid file is opened, the Multimedia control sets the enabled properties of the buttons for the movie. All buttons except the Record and Eject buttons will be enabled.
The sample project for playing AVI movies is on the companion CD as AVIPLAYER.VBP.
To create a sample AVIPlayer program, perform the following steps:
4. Add a command button to the form to allow the user to start the process
of selecting and opening an AVI file. Name the command button cmdAVI and
set its Caption to Get and Play AVI Movie.
5. Place Label controls on the form to identify and hold the Length
and Position information for the movie. At this point, your form should look like
the one in Figure B3.11.
6. Place the code in Listing B3.6 in the Click event of the command
button. This code uses the common dialog to retrieve the file and then sets up the
Multimedia control.
Private Sub cmdAvi_Click() cdlGetFile.Filter = "AVI Movie Files (*.avi)|*.avi" cdlGetFile.ShowOpen mmcAVIPlayer.DeviceType = "AVIVideo" mmcAVIPlayer.filename = cdlGetFile.filename mmcAVIPlayer.Command = "Open" lblStatus(0).Caption = mmcAVIPlayer.Length End Sub
FIG. B3.11
The basic setup for playing AVI movies.
One final piece of code that you need is a line to update the current position of the movie. The following line of code should be placed in the StatusUpdate event of the Multimedia control:
lblStatus(1).Caption = mmcAVIPlayer.Position
NOTE: The length and position of an AVI movie is specified in frames instead of a time.
You can now run your program and start playing movies. After the program has started, you can click the command button to bring up the dialog box to open a file. After you have specified a valid file name and opened the file, the Multimedia control enables the appropriate buttons. You can press the Play button to start the movie. When the movie starts playing, it is shown in a separate window from the one that contains your Multimedia control. Figure B3.12 shows an AVI movie from a Windows help video being run in a separate window.
FIG. B3.12
Movies typically run in their own window.
NOTE: There are a number of AVI movies in the VBOnline folder of your Visual Basic installation.
If you want the movie to run on the same form as your control, you can set the hWndDisplay property of the Multimedia control to the hWnd property of the form. This causes the movie to run in the background of the form. However, running the movie this way can cause problems with the display of controls such as labels. A better solution is to place a PictureBox control on the form and use it to display the movie. The following line of code causes a movie to be run inside a picture box on the form:
mmcAVIPlayer.hWndDisplay = picMovie.hWnd
Figure B3.13 shows the movie running inside the PictureBox control.
FIG. B3.13
Run movies in a picture box to better control their location.
The setup for a MIDI file player is almost identical to that of the AVI movie player. Your program needs a way to specify and retrieve a file, and then to open the file and start playing the MIDI music. When a valid MIDI file has been opened, the Prev, Next, Play, Pause, and Stop buttons of the Multimedia control are enabled.
The key difference between the player for MIDI files and the player for AVI files is the setting of the DeviceType property of the Multimedia control and the Filter property of the CommonDialog control. For MIDI files, you need to set the DeviceType property to Sequencer. This defines the MIDI device to the Multimedia control. Figure B3.14 shows the MIDI player application and Listing B3.7 shows the code to make it run.
FIG. B3.14
A MIDI player created with the Multimedia control.
Private Sub cmdMIDI_Click() cdlGetFile.Filter = "MIDI Files (*.mid)|*.mid" cdlGetFile.ShowOpen mmcMIDIPlayer.DeviceType = "Sequencer" mmcMIDIPlayer.filename = cdlGetFile.filename mmcMIDIPlayer.Command = "Open" lblStatus(0).Caption = mmcMIDIPlayer.Length End Sub
NOTE: A couple of MIDI files come with Windows 95 and are located in the \Windows\Media directory.
You can use WaveForm Audio (WAV files) in your programs for sound effects and alerts. For example, I have a VB program that reads caller identification information from the phone company and then plays a WAV file depending on who the caller is. The easiest way to play WAV files from a VB application is to use the Windows API function sndPlaySound. The Windows API is a group of Windows functions that you can call from Visual Basic.
To use sndPlaySound, do the following:
Declare Function sndPlaySound Lib "winmm.dll" Alias "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As Long) As Long Public Const SND_ASYNC = &H1 Public Const SND_SYNC = &H0 Public Const SND_LOOP = &H8
4. Call the sndPlaySound function from your program.
Private Sub cmdPlaySound_Click()
Dim lRetVal As Long
lRetVal = sndPlaySound("C:\WAV\MySound.WAV", SND_ASYNC)
MsgBox "Done"End Sub
As you can see from the code example, the sndPlaySound function is fairly simple. It takes two parameters, the name of the WAV file and a constant, and returns a value of type long.
The Flags parameter is used to modify the behavior of sndPlaySound. In the preceding code example, the SND_ASYNC constant indicates that the sound is played asynchronously from the rest of the program. In other words, the MsgBox statement is immediately executed. If the SND_SYNC constant is used, the message box does not appear until after the sound finishes playing. The SND_LOOP constant can be combined with SND_ASYNC to create a continuous background sound, as in the following line of code.
lRetVal = sndPlaySound("C:\WAV\MySound.WAV", SND_ASYNC + SND_LOOP)
The sound continues playing until the program executes another sndPlaySound call.
This chapter has provided you with an introduction to the world of multimedia programming. You have seen how you can add animation effects to your programs and how you can use the multimedia devices of your computer to play music, show movies, play audio CDs, and add sound effects or narrations to your programs. This chapter also touched on a number of other topics that are covered elsewhere in this book. For more information about these topics, refer to the following chapters:
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