Conquering Audio Synching Troubles in Flash Video Washington DC

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Originally published at Internet.com

It's a problem we've all encountered more than once: You're watching Flash Video online, and suddenly the audio is way out of sync with the video. To find out what causes this problem and to learn how to beat it, we spoke with a few FLV experts.

The biggest source of out-of-sync Flash Video is certainly YouTube, where you can watch several videos in a row and catch syncing problems with half of them (or maybe it just seems that way). Many companies use YouTube as a free video hosting service, so it's worth knowing hot to avoid problems

According to a YouTube representative, the site's encoding engine works best when its fed the optimal ingredients. If you're having syncing problems with a video, save your local file in this format first: * MPEG4 (DivX, Xvid) * 320 by 240 resolution * MP3 Audio

The rep also suggested that, if you're working with an MOV file, you convert it to either AVI or WMV prior to uploading.

But what if you're seeing synchronization issues with a local file? We also spoke to Grady Player, an assistant product manager for Sorenson Squeeze, who said that the problem can happen for several different reasons.

Using a video source file with a low bit rate per pixel, whether high-definition or standard-definition, or using a DivX file with a fading watermark can both cause synchronization problems. Also files with extras such as 5.1 audio or sprite tracks can cause trouble in encoding.

Player also says that video creators should match the audio of the source file to that of the output FLV file. So if the FLV will have 44.1KHz audio, start with either that or 22.05KHz or 11.025KHz audio. Starting with 48KHz or 32KHz audio could well lead to audio synchronization issues, since it needs to be resampled by the encoder.

Video has the same issues. A file resampled from 29.97fps to 30fps, or vice versa, will show a discrepancy of 1.8 frames every minute. In a longer work, that can create a serious synchronization issue. Output your video at the frame rate that matches your final FLV file.

The lesson for either type of encoding is to take care that you start with the right format, and everything after that should be perfectly in sync.