[MPlayer-users] Re: Documentation update.

Jonathan Rogers jonner at teegra.net
Sat Sep 13 19:09:03 CEST 2003

D Richard Felker III wrote:
> The only purpose is for encoding mp3 with lame. In the first pass
> ("pass 0") you encode the audio with vbr, and you get the exact audio
> bitrate. Then you can tune the video bitrate for pass 1 and 2 so that
> it exactly fills the CD, maximizing quality. With OGM, you do the same
> thing by encoding your vorbis audio in a .ogg file before you even
> begin video encoding.

Why can't one do the same with MP3? Use LAME to encode the audio, then 
encode video in two passes. Then, put them back together with mencoder.

> The problem with the 3pass code, though, is that it doesn't just
> encode the audio. It also makes a table of input/output frame
> correspondence for A/V sync, but without decoding any video, just
> using info from the demuxer. This will work under ideal conditions,
> but if any frames get dropped by the decoder (e.g. they're damaged
> beyond recovery) or by the vf chain during pass 1/2, the sync
> info from pass0 will be bogus and will result in a bad output file.

What is the purpose of the input/output frame table? What does it do for 
you that an ordinary two pass encode doesn't? Does this have something 
with kludging VBR MP3 into AVI?

Jonathan Rogers

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