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PC File Conversion

Part 4 Multimedia Files - Brian Pickard

In this part I will try and point the way in dealing with multimedia files types when importing and exporting between RISC OS and PC Windows platforms. These types of files are not easy to deal with and certain types cannot be used on RISC OS machines. Let's first break them down into audio and video files.

PC Audio file formats

Wave
The most common audio filetype is Windows Wave (denoted by the file extension .wav) This is used by most CD burners and audio software on the PC. Most RISC OS audio software also understands this format e.g. CDBurn. There are different standards that use this .wave extension! I have come across the following types:

• A/mu-Law
• ACM Waveform
• DVI/IMA ADPCM
• Microsoft ADPCM
• Windows PCM

The actual type is usually recognised by the first few bytes of the file. The Windows PCM starts with RIFF. Even though this complicates matters I have found Mark Scholes PlaySound and Rick Hudsons SoundCon do recognise these variations.

MP3
No problems here RTracker and AMPlayer will play these files.

Real Audio
RISC OS does not support this format (due to copyright restrictions).

PCM format
Some PC and RISC OS software recognise this format. It is just the CD sound format. This consists of two 16 bit values one for each stereo channel. However be careful since there are two standards.

• Intel standard: This has the order LSB MSB.
• Motorola standard This has the order MSB LSB.

RISC OS CDBurn understands the Motorola standard. But the filetype has to be set to DATA. CDBurn also understands the wave format but since there are so many variations I tend to stick with PCM files.

There are other variations that use just 8 bit values with added compression. These include 8 bit mu-law compressed and 8 bit A-law compressed. I wouldn't advise their use, unless disc space is at a premium. To give an example of this file use. I use a PC to capture sounds (archiving my vinyl) and save the tracks as PCM Motorola standard files. Then port them over to my RiscPC change their filetype to DATA and then use CDBurn to produce the CD.

Why don't I transfer my CD writable drive to my PC? Well I have come across PC owners whose lightening fast all bells and whistles burners produce some very strange sounding CDs! My RiscPC CDBurn and old Ricoh writable drive has NEVER produced a bad CD copy! (You can't produce Audio CDs at high speed, if you do things can go wrong, when burning an audio CD on a PC go down to 8 speed - ED).

RISC OS Audio File formats

Replay
This format was invented by Acorn for its video/sound replay application. No PC applications (as far as I know!) will read these files so convert them to wave format.

MIDI files
These are universally understood and therefore any MIDI application will be able to play these files. The only compatibility problem will be the instrument sounds. Best to use the GM MIDI standard as most applications understand this instrument setup.

Using Music Software

The only common music software for both PC and RISC OS I have come across is Sibelius.

This is a music writing application which takes its input from a Midi keyboard and produces music manuscripts ready for printout. It is expensive but if you are a serious musician it is the one to go for.

The Problem with MP3

If you wish to send music files to PC users then use either wav format or mp3 (over the web since it compresses sound files by a factor of 8 to 10). There is one snag with the mp3 format when using RISC OS. There is no easy way of converting wav etc. to mp3. I have found three applications called cmpa, lame and blade that will convert wav or pcm files to mp3 but these are all command line apps. Justin Fletcher did produce a multitasking front end for cmpa but at the moment he has taken his apps off his website.

I have produced a wimp multitasking application which uses Lame. I chose Lame because it has two versions, one for StrongArm and the other for ARM7500FP cpu. It is on the CD and is called !MakeMpeg.

The help file contains the user guide. Don't expect the conversions to be quick (unless you have one of the latest RISC OS computers). I would like to know how quick so I have included a wav sound file called testtrk. It is a track from a friends own made CD of his own songs. It is approximately five and a half minutes long. On my StrongArm RiscPC it takes about 25 minutes to convert it to an mpeg. I think it should be quicker using an XScale or the ARM7500FP (the latter may be a surprise but it is due to the built in floating point co processor). Lame will also convert MPEGS to WAV or PCM too. (A much quicker process!).

If you wish to port a sound file over the net then use mp3. If you wish to let a friend have a track then using a CDR or CDR/W use the WAV format.

The Problem with Video Files

Lets deal with the ones RISC OS does not recognise.

REAL (extension .rm)
This is used to send small screen video over the net using the Real Player by Real Networks. The BBC use this extensively on their web site. Due to copyright restrictions RISC OS does not have any way of playing these files.

DivX
This is a highly compressed video format. I have not found any RISC OS applications that can play these files.

Now for the good news the following formats can be viewed using RISCOS computers.

MPEG videos
These can be played by using the KinoAMP application which always under development. You will need at least a StrongARM machine. You can find further details at www.eqrd.net.

Apple QuickTime (file extension .MOV)
These can be played via a plugin for RISCOS (via !MovieFS), !ARPlayer.

Warm Silence Software do several plugins for different file formats that allow the !ARPlayer to view PC video formats. These include PC files that have file extensions .FLI .FLC .AVI .WAV. Note the last two are Windows filetypes and dont be confused with .WAV. This extension is used for both video and audio files.

The main problem is that there is no cheap and easy way of producing video files on the RISCOS platform (unless you know different!).(Well there is one free video editor, it's called CineWorks, and I have put a copy in the software directory - ED)

Animations
If you want to produce animations you can use your favourite drawing program and use a screen grabber to produce a series of sprite files. Then use !InterGIF to produce animated GIF files.

Most PC video editing software will allow animated GIFs to be loaded and therefore converted into .WAV etc video files. I have used this method when requiring an animated diagram for a video.

As you can see video format is one area where the RISC OS world needs to 'catch up'.

One note though, the BBC use an editing suit based round a RiscPC! It is called OPTIMA and I believe the RiscPC podule is being sold (second hand) by CJEMicros! So if you are an enthusiast then perhaps this is worth investigating.

Thats it for this part, next time I will try and delve into Desktop Publishing.

Brian Pickard