[MEncoder-users] Telecine and B frames for DVD

[Walter R. G. Hachmann]

Hi, everybody

I've just discovered that mencoder doesn't like B frames when the soft 
telecine option is active.
I encoded a 23.976 progressive ntsc film from a DVD and got strange 
jumpiness in the final DVD.
The following command was used:

mencoder lola.vob -o lolabtc1.mpg -vf harddup -oac copy -ovc lavc \
-lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=8000:\
vbitrate=6000:keyint=18:vmax_b_frames=2:vstrict=0:aspect=16/9 \
-of mpeg -mpegopts format=dvd:tsaf:telecine -mc 0 -ofps 24000/1001

In order to see the problem, you need to create a dvd with a tool like 
DVDStyler/dvdauthor
from the encoded file, previously remuxing the streams to make sure it 
is compliant with dvdauthor,
burn it to a DVD-RW and play it in a standard standalone DVD player. You 
won't see the problem
by playing the DVD with xine or mplayer. For example:

mencoder lolabtc1.mpg -of rawvideo -oac copy -ovc copy -mc 0 -ofps 
24000/1001 -o lolabtc.m2v

mencoder lolabtc1.mpg -of rawaudio -oac copy -ovc copy -mc 0 -ofps 
24000/1001 -o lolabtc.ac3

mplex -f 8 -o lola-final.mpg lolabtc.m2v lolabtc.ac3

The strange thing is that if I don't use B frames (vmax_b_frames=0) the 
DVD will play a perfect
movie, no jumps at all. Before somebody tell me I have a buggy player, I 
inform I did the same
test using another coder with B frames, the program mpeg2enc, like the 
following:

mpeg2dec -s lola.vob -o pgmpipe | pgmtoy4m -a 40:33 -r 24000:1001 \
-i p | mpeg2enc -f 8 -R 2 -b 8000 -q 8 -g 6 -n n -a 3 -p -v 1 -o 
lolabtc2.m2v

mplex -f 8 -o lola-final2.mpg lolabtc2.m2v lolabtc.ac3

Using the lola-final2.mpg video to make a new DVD compilation gave me 
good results,
although coding with mencoder is much faster and the final results look 
better.
By the way, playing the original or the reencoded files gives me the 
mplayer message
"demux_mpg: 24000/1001fps progressive NTSC content detected, switching 
framerate.",
 so I'm sure it's progressive.

I did several test, both with Christian Marillat's etch version of 
mencoder and with version 1.0rc2
compiled from source. In both cases, same results.

Do we have a mpeg muxer bug here???

Regards,

Walter



-- 
*/Walter R. G. Hachmann/*
phone: +55 (11) 3744-3487
mobile: +55 (11) 8585-2545