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mp4a to ac3/mp2 ?

Discussion in 'Other video questions' started by cinezone, Apr 10, 2006.

  1. cinezone

    cinezone Member

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    Hi,

    I'd like to create a demo dvd with a lot of new trailers. I download them from apple in HD 720p and then reencode them with AviSynth and HCEnc. It works fine but I have a problem with the audio stream.
    In their files, they use mp4a and I don't know how to convert it to a dvd format (ac3/mp2). At this time I can convert the stream in LPCM 2 channels with mplayer but this is a demo disc so I'm looking for 6 channels.

    Thx.
     
  2. celtic_d

    celtic_d Regular member

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    ffmpeg and I'd definatly go with AC3 over mp2.
     
  3. cinezone

    cinezone Member

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    It doesn't seem to work or I don't know how to use it.
    I tried to load the .mov file. I suppose I have to demux the audio and video from the file before using ffmpeg but how do I do that ?

    Thx
     
  4. celtic_d

    celtic_d Regular member

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    libavformat has an mov demuxer, so there should be no need to demux before hand.
     
  5. celtic_d

    celtic_d Regular member

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    Errr, seems ffmpeg doesn't like the 5.1 aac in quicktime trailers. Don't know why Apple can't just use mp4 as a container. You could try demuxing.

    edit: looks like ffmpeg might have issues with all 6 channel aac.

    mplayer should be outputting 6 channel pcm audio though which ffmpeg can convert or you could use mencoder, then demux the audio. mencoder.exe -ovc frameno -channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384 input.mov -o output.avi

    Unlike ffmpeg though I don't think there is any way to directly output an audio only stream.
     
    Last edited: Apr 11, 2006
  6. cinezone

    cinezone Member

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    My mplayer doesn't play 5.1 files, it detects only 2ch...
     
  7. celtic_d

    celtic_d Regular member

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    Default is 2 channels. If you have more than two speakers then you should have set in your config. channels=6. mencoder doesn't read the config file so you need to specify. You can do the same with mplayer to. Just that it is easier to set default options in the config (fullscreen, subtitle font, menu, etc.).
     
  8. cinezone

    cinezone Member

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    Yep, but when I use channels=6 I've a problem with the sound which seems to play very very slowly. It's the same if I use channels=4.

    Could you try on your side if it works ? (I'm under windows xp)
     
  9. celtic_d

    celtic_d Regular member

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    Works fine here. I've had channels=6 in my config file for ages. -channels 6 worked fine to convert a mov trailer earlier to. Trailer in question was cars-tsr4_h720p.mov

    mplayer/mencoder build used was from the 10th.
     
  10. cinezone

    cinezone Member

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    If you're under windows, can you tell me where do you find so updated builds ? The one on the official website is "MPlayer dev-CVS-050928-16:38-3.4.2"

    Thx
     
  11. celtic_d

    celtic_d Regular member

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  12. cinezone

    cinezone Member

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    Great job, it's working now, so thank you for the tips and the builds.
     

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