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Old 28th May 2005, 18:59   #1  |  Link
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Joining MP4 - synch issues


I am having synch issues when trying to join MP4's:

The film is Fellowship of the Ring - 2 DVD, compressed to AVC +2xAAC ( +2xttxt +chapters), the seperate 1st and 2nd parts are fine. After muxing (with MP4Box), A/V synch breaks at the end of the fist and beginning of the second part.

YAMB/MP4Box tells the video in part 1 is 1:41:18:840 long, and the two audio streams are 1:41:17:909 - difference could be the source of the problem..

Question is: is it a bug in MP4Box, or is it a bug in the user?

EDIT: just checked the ttxt subtitles, they have the same problems as well..

Last edited by LRDX; 28th May 2005 at 19:09.
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Old 28th May 2005, 19:52   #2  |  Link
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afaik that is caused because of how the stream is stored on the second dvd

you might want to search in the dvd section for this special problem happening with the lotr dvds, i think there are too many/few frames in the beginning of the second dvd or so, but i dunno it exactly
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Old 31st May 2005, 00:57   #3  |  Link
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Problem @ the first disc

Hi again!

Tried applying a 931ms delay (the difference I mentioned in the first post) on the audio track of the 2nd disc's audio tracks, and.. worked.

So the problem was (is), that MP4Box simply joined all streams disregarding that the audio was shorter than video on the first disc, so the second disc's audio got a 931ms haste. Silence has to be inserted between them to have proper A/V synch.

Don't know if it can be considered a bug, I dont expect a multiplexer to know the "silence" frames of all usable audio codec, and have them inserted when necessary..
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