Finding Interesting Times
The Movie Toolbox provides a set of functions that help you locate samples in movies, tracks, and media structures. These functions are based on the concept of "interesting times." An interesting time refers to a time value in a movie, track, or media that meets certain search criteria. You specify the search criteria to the Movie Toolbox. The Movie Toolbox then scans the movie, track, or media, and locates time values that meet those search criteria.You can use these functions to search through image sequences. For example, you may want to locate each frame in an image sequence. Or you may be more interested in key frames, especially if you are trying to optimize display performance. In image data, sync samples are referred to as key frames. For more information on key frames, see the chapter "Image Compression Manager" in this book. An easy way to determine whether a movie has been edited is to look for track edits in the movie data. You may also be interested in searching for samples in a movie's media. If you set the appropriate search criteria, the Movie Toolbox locates the appropriate frames for you. You need the functions described in this section because QuickTime doesn't have a fixed rate. Each frame can have its own duration.
The Movie Toolbox identifies an interesting time by specifying its starting time and duration. The starting time indicates the time in the movie, track, or media where the search criteria are met. The duration indicates the length of time during which the search criteria remain in effect. For example, if you are looking for samples in a media, the start time would indicate the beginning of the sample, and the duration would indicate the length of time to the next sample. In this case, you could find the next media sample by adding the duration to the start time. These duration values are always positive--you determine the direction of the search by setting the sign of the rate value you supply to the functions.
Note that movie interesting times are defined in the scope of the movie as a whole. As a result, one interesting time ends when another interesting time starts in any track in the movie. For example, if you are looking for key frames in a movie, the duration value from one interesting time tells you when the next key frame starts. However, that second key frame may be in a different track in the movie. Therefore, the duration of the interesting time does not necessarily correspond to the duration of the key frame.
You can use the
GetMovieNextInterestingTimefunction to locate times of interest in a movie. TheGetTrackNextInterestingTimefunction lets you work with tracks. Use theGetMediaNextInterestingTimefunction to locate samples in a media.
Subtopics
- GetMovieNextInterestingTime
- GetTrackNextInterestingTime
- GetMediaNextInterestingTime