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Problems with splitting avi files

Discussion in 'DivX / XviD' started by GeMinH, Apr 11, 2005.

  1. GeMinH

    GeMinH Member

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    I've recently used Virtual Dub 1.3c in order to split large avi files. In the process of doing so, I didn't hold onto shift on a keyframe but instead I used the "Go To" option in edit and jumped to the preferred frame. After saving the new file, I re-watched the avi file for problems of synch and everything was perfect. But after burning the files onto a VCD, I watched it again only to find that the audio was out of synch with the video. (The file goes through scenes perfectly around 30 min and suddenly the audio starts going faster than the video)
     
  2. celtic_d

    celtic_d Regular member

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    Sounds like your problem is converting the avi's and not splitting.
     
  3. aldaco12

    aldaco12 Active member

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    Yes, I agree. Usually you keep VirtualDub's settings to Audio___Direct Stream Copy and Video___Direct Stream Copy, so there's no reson for the movie don't remain in A/V sync due to the splitting.
    Usualy this happens only when the AVI's MP3 audio stream is encoded VBR and instead of CBR. This makes the AVI --> MPG conevrsion go mad and you need to uncompress the whole audio stream, first (use VirtualDub; set Audio__Full Processing Mode without setting any compression and do File__Save WAV), and use that BIG (1.2 GB for an average movie) WAV file as 'audio input' (e.g. by TMPGenc) instead of using the default AVI's audio stream as 'audio input'.
     
    Last edited: Apr 12, 2005
  4. The_OGS

    The_OGS Active member

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    I know! I agree - it shouldn't, right?
    But it will often lose sync in the second segment (the first cut segment) if the AVI was not interleaved every 1 video frame. If interleaved, say every 10 video frames, you will require very good luck to cut on both a keyframe and an 'interleave-frame' - practically impossible :^(
    I would consider using Nandub to re-interleave the AVI, the large original AVI, every 1 video frame. A 10 minute job.
    If the file grows in size, it needed doing ;^)
    Nandub works with AC3 and VBR MP3 audio.
    To encode VCD (MPEG1?) you should give TMPGEnc a WAV file to encode using its own encoder, as Aldaco12 has said.
    Have you considered doing the 1 big AVI directly, and causing TMPGEnc to split the output into 2 (or 3 or 5, I dunno) VCDs?
    I mean, avoiding the AVI-cutting would be good but if you must cut, try the Nandub for VBR or AC3 audio.
    Regards
     
    Last edited: Apr 12, 2005
  5. GeMinH

    GeMinH Member

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    Hey, thanks for reply people. Now my avi files are perfect even on the DVD with A/V sync!
     
  6. aldaco12

    aldaco12 Active member

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    Just to know a little bit of theory, the problem lies in the fact that if you compress the WAV sound stream to MP3 using VBR (Variable Bit Rate) , like you would do for music, the AVI --> MPG conversion, which is based on a CBR encoding of the movie video, goes crazy. That 'uncompressing the audio to WAV' I suggested you is needed just to remove that "incompatible" CBR compression.
    The people who know better this problem, encode the AVI's MP3 audio using a "CBR MP3 encoding".
     
    Last edited: Apr 18, 2005
  7. The_OGS

    The_OGS Active member

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    You mean, of course, the incompatible VBR compression...?
    Well sure, I could make DVD backups using CBR audio - but it wouldn't sound as nice, and I'm not at all interested in making AVIs that are most easily converted back into MPEGs again :^)
    But it's true - VBR MP3 should be decompressed to WAV before any transcoding conversion to another format.
    WAV is a CBR format (with a great whopping bitrate) so a file's size can quickly be calculated from its length & vice versa = no surprises for an encoder.
    L8R
     

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