[MPlayer-users] 2 pass divx encoding from .VOB/dvd - Targeted filesize (bitrate) ends up way way wrong

[Øyvind Stegard]

D Richard Felker III wrote:

>[Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
>On Mon, Aug 19, 2002 at 10:34:46PM +0200, Øyvind Stegard wrote:
>  
>
>>[Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
>>Hey
>>
>>I'm trying to encode a ~2 hour DVD, targeting two 80 min CDRs (about 
>>1400MB). My problem is essentially that the bitrate I specify to 
>>libavcodec is not respected at all and the movie ended up at half of the 
>>filesize I had targeted(resulting in rather poor quality). (It turned 
>>out to be ~700MB when I specified an average bitrate that should result 
>>in a file close to 1400MB (audio stream taken into consideration)). To 
>>clear things up, here are the two command lines I used:
>>
>>1. pass:
>>mencoder dogma.vob -nosound -ovc lavc -lavcopts 
>>vcodec=mpeg4:vbitrate=1400:vhq:vpass=1 -vop scale=672:288,crop=701:429 
>>-sws 2 -o /dev/null
>>    
>>
>
>-lavcopts vqmin=2, or even 1 perhaps with bitrates this high.
>Actually, I believe there *is* a bug in libavcodec where it won't
>properly distribute bits on the second pass when the minimum qscale
>(vqmin) is already reached on lots of frames, so quality still won't
>be ideal, but it should be a lot better.
>
>Also don't use -nosound, that will cause mencoder not to mess with a/v
>sync, which could cause the frame numbers in lavc_stats.txt to be
>totally wrong for the second pass!! Instead use -oac copy or -oac pcm
>(doesn't matter since the output is going to the bitbucket anyway).
>
>  
>
>>Finally, some more details:
>>The movie is 720x576 PAL 25fps, about two hours long. I also got 
>>indications (from a reply to a previous post I sent), that the movie 
>>probably was a field based interlaced stream. It was ripped using Smart 
>>Ripper on a windows box, and the .vob file (concatenated all vobs to 
>>one) is about 6GIGs, and contains video, two ac3 streams (one 2.0 and 
>>one 5.1), and some subtitle stuff.
>>    
>>
>
>You might need -ofps 50 or something. Read the archives. Broken
>interlacing will definitely have a huge negative impact on
>quality/bitrate.
>
>  
>
>>Also, when I try to use the external -pass 1/2 parameter (instead of 
>>libavcodec internal vpass), the bitrate goes much much higher than it 
>>should, so that's a no-no. (Does the external -pass 1/2 really work well 
>>with libavcodec ?? It looks very DivX5 oriented)
>>    
>>
>
>No, it's broken with libavcodec and should not be used. It might
>partially work if you have b frames turned off, but it's still a bad
>idea.
>
>Rich
>
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>
>  
>
Thanks for the information, I actually saw a note on the man-page that 
said to avoid the external bitrate control combined with libavcodec, 
right after I posted. (RTFMP, I guess:).

I'll try with vqmin=2, and if this doesn't work out either, I'll go with 
DivX5 and external bitrate control.

DivX5(libdivxencore.so) + external bitrate control works fine, right ?? 
I don't need to set any special divx4opts then ? This I ask, because 
I've noticed that all the numbers in the the divx_log file are "0" 
except for the "total" number and frame number, and I find this a bit 
peculiar.

--
Øyvind S.