AVI [was: [MPlayer-users] Re: divx 6 ]

[Alexander Noe']

Corey Hickey schrieb:

>>Did Koepi tell you that?
>>
>>AVI has been able to hold 256 streams [1] since it was introduced like 
>>15 years ago. Besides that, you can't use subtitles in any language 
>>but english if you want your OGM file to work without forcing the 
>>watcher to handle charset stuff.
>>
>>AVI, on the other hand, works with utf8 subtitles, so there is no 
>>problem as long as you don't want to use original klingon. The *only* 
>>new thing about OGM was that it worked properly with VFR streams.
> 
> 
> Assuming you refer to "variable frame rate", then Michael wrote
> something interesting about that in his blog:
> 
> http://guru.multimedia.cx/the-avi-container-file-format/

I said "properly" ;)

This is the interpretation ffmpeg is using when storing vorbis in avi. 
I have read support for this in AVI-Mux GUI (the vorbis init packets 
are stored in a b0rked way, that's why it needs special support), I 
know that it can be done this way. It is spec compliant, yes...

>     again this isnt true, storing variable framerate in AVI is not
> efficient but it is possible and its not a hack and it doesnt stretch

"not efficient" is a nice euphemism. Even when improving this method, 
p.e. by setting AVIF_MUSTUSEINDEX (breaks mplayer, right?), providing 
one 0-byte-frame and then pointing to it several times in the index 
instead of having multiple copies of 0-byte-frames (with 8 bytes chunk 
header each), it is still euphemistic to say it isn't efficient.

The problem is that long Vorbis frames are typically 8 times as long 
as short frames, so that even if you base timing on the duration of 
one short frame (and not less), you need 8 filling frames, which means 
64 bytes of overhead when using the method I described above, or 128 
bytes when not using this method, or 192 bytes when not using this 
method and not using Open-DML.

If frame durations can differ even more, it gets worse.


Alex


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