Where is audio/video sync data located in video files?
 

What information in a video file does the VLC player read in order to know how to synchronize the audio with the video? Is it information in the header and if it is, what exactly in the header data does it look for?

The reason I ask is that I recently downloaded a file which had an audio sync problem on my Mede8er X3D mediaplayer (and my WD Live for that matter) but it plays without issue on my PC in the VLC Media Player. What I would like to know is what data in the header (or wherever the data is located) is VLC interpreting correctly and that the X3D is either misinterpreting or disregarding completely and is there anything that I can do to make this data intelligible to the X3D? It's just piqued my curiosity and I figure there must be a program out there to remedy this on my PC by manipulating the affected data.

Many thanks.

It's in the "flags" of the file. Sync is controlled by several things -- the delay, the interleaving, etc.

I've run into similar issues, from time to time, on WDTV and XBMC. The issue is related to the decoders and/or the software that did the sync to begin with. I've always found that loading the file into TMPGEnc Smart Renderer 4, and changing the offset by just 1 frame on the "okay but not okay" files, would cause it to be rewritten and thus work fine in the same WDTV or XBMC.

Thanks so much for the reply!

I'll give that a go later, see how it works out for me, and respond back. :)

-- merged --

Rather than render the entire file each time I experiment with the offset times, can I just cut a segment out of it and render that? What would be the best program to do the cutting with? I understand render times can be long in TMPGEnc.

-- merged --

Well I don't guess I will after all. The trial version of TMPGEnc MPEG Smart Renderer 4 doesn't let you save a project rendering (no pun intended) it completely useless for my purposes. I'm certainly not going to purchase software until I know whether it suits my needs or not. Trial version in this case is certainly a misnomer. Can you suggest another app?

Avidemux can, sometimes, cut H.264/MP4/MKV files, but no always. That is a distribution format, as is not really meant to be edited (cut, spliced, etc). It's sometimes not easy.

Where do you read that? It's not true for TMPGEnc SR4. A 45-minute video file usually takes 2-3 minutes max to resync the audio.

You don't really need to export it to see the audio changes -- it previews live. What you see is how it saves the file. As far as other software that can do this, I've never seen anything.

I need to save the file and play it back on my mediaplayer to check and see if the altered setting has made any difference. On my PC the file plays fine as it is.

How big is the file?
And what is the offset?
Perhaps I could do it for you. I own TMPGEnc SR4.