AVI/xvid/ac3-copy video re-compress audio

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gfischer
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AVI/xvid/ac3-copy video re-compress audio

Post by gfischer » Tue May 03, 2011 6:31 pm

I've been using MediaCoder for a while and I like it a lot, I now use build 5138. However, recently I have become stuck with a file from hell that does not want to be converted in the way that I want. It is a 941MB AVI file with MPEG-4 Visual, XVID, 796 kbps; the audio is AC-3 @ 448 kbps and the resolution is 592x320 @ 25 fps. I want to convert it to a lower audio rate as I think that 448 kbps is unnecessarily high and at the same time reduce it's overall size without changing any video settings. Ideally, I would like it to be 700MB so it will fit a CD (which very likely means I have to lower some video settings as well), but no matter what I tried it never does that. I've tried "copy video" with different audio settings', "disable video", different video bitrates, VBR, CBR, MP3 and AC-3 formats with lower bitrates, almost anything. What I get are either files that are bigger than the original (over 1 GB), files that do no not have any video but only audio or files that play ok halfway and then the audio becomes very slow and the duration goes over 5 hrs instead of 1:44.

What am I doing wrong here?

Thanks

ladycoder
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Re: AVI/xvid/ac3-copy video re-compress audio

Post by ladycoder » Fri May 06, 2011 4:14 am

Try getting a bitrate calculator:

A video of 1hour 44 minutes with audio of 448kbps - the audio alone is 333mb !

So dropping the audio bit rate is definitely enough to fit the video on a cd.
A bitrate of 128kbps =95mb + overhead so might be the trick. Try CBR MP3 - lame or helix (if that is still an option)

Try disabling video converting the audio and muxing the 2 together with AVIMux_Gui or Virtual Dub. VBR video may be part of the copy video problem.

As long as the audio alone is the right length and speed and in sync, you can mux the 2 together with anything.

Also 448kbps audio usually means 6 channel, so make sure. This can affect conversion to 2 channel mp3 or ac3.

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