Author Topic: Investigating timing offset  (Read 402 times)

dosdan

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Investigating timing offset
« on: January 14, 2018, 09:36:46 PM »
Here's a 60MB MP4 test file: https://dl.dropboxusercontent.com/s/gzypkud0x9g9un4/400m_finish_straight.mp4

I'm using MP4 Inspector: https://sourceforge.net/projects/mp4-inspector/

I load the test MP4 into ADM (20180113 w64 nightly).

I specify a 500ms shift and Copy/Copy/MP4 & Copy/Copy/MP4v2, and save to new file names.

1. Where do I look in MP4 Inspector to see/work out the timing offset, if any, of the .mpa stream in the original MP4?
2. Where do I look to see/work out the 500ms change in the timing offset in the MP4 after ADM has worked its magic?
3. Is a 500ms shift change advancing and -500ms delaying the audio relative to the video?

Dan.
« Last Edit: January 14, 2018, 09:54:27 PM by dosdan »

eumagga0x2a

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Re: Investigating timing offset
« Reply #1 on: January 14, 2018, 10:28:11 PM »
Positive shift values: delay audio. Negative shift values: advance (skip the beginning of) audio. The former doesn't work with MP4 in Avidemux (the result, saved by Avidemux, works fine e.g. in mpv), which should be a bug.

I don't think negative shift values are stored at the container level at all, unsure about positive ones, must look into the code first.