Technical Q&As


QTW 09 - Sound/Video Sync Problems (1-May-95)


Q I'm having video/sync problems with QuickTime for Windows. What's going on?

A Here are some things you need to be aware of:

1. Make sure that the movies are flattened and interleaved. If your audio track is marked as "preload," you will have problems since the audio doesn't truly get interleaved with the video data. Remove the preload attribute if present. Atool such as MovieAnalyzer will also show you the data interleave.

2. Many PC's do not have their 16-bit audio properly configured at a hardware level, and there may be conflicts between 16-bit audio and devices such as your CD ROM. Rearranging DMA channels (high DMA) and IRQ can help. Try testing with a movie which only has an 8-bit audio track, to isolate the problem.

3. 150k/sec will probably not work on a PC single speed CD ROM drive and will cause video jerkiness. Downsample to 110-120k/sec for compatibility with most PC CD ROM drives.

4. Make sure that the audio track in your movie has MPC audio rates. Many PC sound cards falsely report their capabilities with respect to converting the audio rate and QuickTime for Windows trusts those reports unless you perform some overrides in the QTW.INI file. A tool such as dumpster should show exactly 22050.0000 for the audio track's STSD atom (any other rate is likely to cause problems on some sound cards.

Technical Q&As
Previous Question | Contents | Next Question