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  1. I want to add second audio stream to video from another video.

    video 1: mp4 x264 AAC audio
    video 2:Avi Xvid MP3 audio (audio taken from it)

    The way I tried to sync the audio was by opening both videos with Avidemux and measure the difference of timestamps between identical I-frames and set the exact delay.
    I was surprised to find out the new audio was not in sync (constant delay) by quite a big margin.

    Can anyone think of a reason?
    Maybe an original delay resets when I apply the new delay?
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  2. Member budwzr's Avatar
    Join Date: Apr 2007
    Location: City Of Angels
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    You should decompress all audio to WAV/PCM 16/44 before trying to sync or overdub.
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  3. Member hech54's Avatar
    Join Date: Jul 2001
    Location: Yank in Europe
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    Originally Posted by roalush View Post
    Can anyone think of a reason?
    MANY reasons.
    PAL source vs. NTSC source.
    Different actual start time/position(silence at the beginning of the audio).
    44.1K vs. 48K audio.
    etc etc etc

    I convert both audios to .wav, load them into an audio editor(like Reaper), adjust the audios to start
    at the same time, then watch to see if they proceed synced. If not I adjust the playback rate of the second
    audio file to match the original. This takes a LONG time to adjust perfectly. Some times it takes me up to 15
    minutes just to adjust a 4 minute music video.

    Have fun.
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  4. Originally Posted by budwzr View Post
    You should decompress all audio to WAV/PCM 16/44 before trying to sync or overdub.
    How do know if decompressing does not change the audio time codes?

    I've heard of ffprobe, maybe it can help me understand how video and audio frames are synced so I can resync the audio to the other video file?
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  5. Member hech54's Avatar
    Join Date: Jul 2001
    Location: Yank in Europe
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    You can't just stick audio from another file/source to a different video. Whoever told you that is an idiot. Even if you take a VHS capture of a movie and try to attach it to the DVD version of the same exact movie, it WILL take time, effort and knowledge to make it work.....even if they were both the same video format(PAL to PAL, NTSC to NTSC).
    There are way too many variables in the way of you just muxing these two together and having them sync perfectly. You have to forget about the original AAC audio and concentrate on editing and time-stretching/shrinking the (now)uncompressed MP3 audio to match the video. No time codes, no time stamps....these are from two completely different sources.
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  6. I know I can just add the audio, look at the lip sync and adjust it manually, but I want a more accurate method.
    I've read a document issued for Tv networks that a human eye cannot detect delays of -100 ms to +25 ms

    Originally Posted by hech54
    I convert both audios to .wav, load them into an audio editor(like Reaper), adjust the audios to start
    at the same time, then watch to see if they proceed synced. If not I adjust the playback rate of the second
    audio file to match the original. This takes a LONG time to adjust perfectly. Some times it takes me up to 15
    minutes just to adjust a 4 minute music video.

    Have fun.
    hech54's method is the best approach, but in my case I've examined both videos and they are the exact same length and have 99.99% same video I-frames. Both audios are the exact same length either. If they are not I have methods to get them to match.
    The only thing I don't know, and what I want to learn, is how to detect the synced time codes of video and audio so I will be able to take audio from one video and put it at the exact same relative spot at another video. This should be faster and scientifically accurate, I hope this is possible.

    I prefer to use ffprobe but I still don't know how to understand the reports they generate or if I could read such delays with it.
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  7. Member hech54's Avatar
    Join Date: Jul 2001
    Location: Yank in Europe
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    Originally Posted by roalush View Post
    what I want to learn, is how to detect the synced time codes of video and audio so I will be able to take audio from one video and put it at the exact same relative spot at another video. This should be faster and scientifically accurate, I hope this is possible.

    I prefer to use ffprobe but I still don't know how to understand the reports they generate or if I could read such delays with it.
    I don't know where you are getting this "time codes" nonsense(sorry, there is no other word for it) from. There is no time code. There is no time stamp. There is no extra data file you can take from one video's audio and attach/plug in to the other video's audio to make it behave the same way. It doesn't exist.
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  8. Thanks, I'll give reaper a try.
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