TechNote (Archived)

What are some ways to synch audio in Flash?

Sound synching strategies
There are different approaches to synching audio and visual content. The method used should be chosen on a case by case basis, depending on the content and scope of the project. For another article on this subject, please see an interview with Alex Kilgo.

The easiest way is to use short sounds that are triggered when the playback head reaches a certain frame. If a long narrative track is being used, break up the sounds into sentences or paragraphs that describe a certain section of the movie. Make sure the playback head stays in this area long enough to play the entire sound. It's much easier to tie specific sounds to specific frames, than it is to play very long sounds.

If a longer sound file must be used, consider using the "stream" synch method, available in the Sound Panel of the Frame Properties dialog box. This will force Flash to drop frames (if necessary) in order to keep up with the audio.

If the project demands that each and every frame of the animation is seen, then try setting a slower frame rate. Unlike QuickTime, Flash and Shockwave both use the frame rate as a top gate: the playback will try to meet that rate, but will not exceed it. By controlling the playback dimensions of the movie and by testing on a slower machine, constant playback rate across different machines can be achieved.

Synchronize audio in the destination environment
If this Flash movie will be playing in another environment, such as QuickTime or Director, then it is often more efficient to synchronize audio in the destination environment. This is particularly true with time-based QuickTime files: instead of combining an event-based Flash animation and a time-based audio file in Flash, and then converting both to a time-based QuickTime stream, it is usually easier to first convert the event-based Flash animation to a time-based QuickTime stream and then to strip in a time-based audio track. (Rephrased, the synch process is facilitated if all the elements are already time-based, rather than attempting to match time-based and event-based streams and then converting everything to another time-based stream.)

When working in Director, it is usually best to use simpler Flash movies... instead of building all the interactivity and audio into a nested Flash file, keep the control at the top level so it will be easier to edit later. The Flash movies can send frame events out to the Director host, letting Director know when it should play certain files. By sending messages out to Director, audio cue points can be used for synching, and the "lock step" option can keep Flash frames in synch with Director frames.

Summary
There are many delivery paths where audio synchronization might be desired. Because of this, one approach doesn't work for all cases. Try experimenting with different methods to find the way that suits a specific project. Smaller sound files will make the process easier and testing on slower machines can ensure consistent playback. Also remember that delaying the synchronization procedure until the project is in the final delivery environment can improve workflow and efficiency.