Asynchronous Movie Loading

QuickTime supports the asynchronous loading of movies. This method is the preferred mechanism for instantiating movies located on a network or other slow link. In fact, asynchronous movie loading can be used in all movie-loading situations with QuickTime taking care of which load model to use.

Non-Asynchronous Load Model:

NewMovieFrom... <playable> <complete>

Non-Asynchronous Load Model:

NewMovieFrom... <incomplete> <playable> <complete>

There are a number of advantages to using the asynchronous model. To the user, it can mean a more responsive system. The difference in user experience centers on the time before the movie data has actually been located and processed. To the developer, it can mean more time to do things while a movie loads in cases where it can take some time for enough data to arrive to allow the movie to play. For example, very large movie files over a slow network connection.

Instead of a fully formed movie being immediately available and playable, NewMovieFrom... functions will return a valid movie, but that movie may be completely empty. For example, it may contain no tracks, user data etc. At some point, when the movie resource is found or the file has been imported this information becomes available and the movie is 'playable'.

To enable asynchronous loading when opening a movie, an additional flag (newMovieAsyncOK) is passed to one of the NewMovieFrom... functions. Without this flag, calling one of the NewMovieFrom... functions returns either a fully formed movie or an error.

During the time when the movie state is kMovieLoadStateLoading the movie cannot be worked with. To determine when the movie becomes kMovieLoadStatePlayable use the GetMovieLoadState function, this call will return a value indicating the current movie state.

kMovieLoadStateLoading - QuickTime instantiating the movie.

kMoiveLoadStatePlayable - movie fully formed and can be played.

kMovieLoadStateComplete - all media data is available.

kMovieLoadStateError - movie loading failed.

References

Introduction to Asynchronous Movie Loading