[FFmpeg-devel] Mpeg2 encoder can't break through the Quantizer 2 barrier ?

[christophelorenz]

I'm trying to encode very high bitrate video in HD with bitrates upto 
80Mbits in mpeg2.
Seems the bitrate management has problems to use quantizers lower than 
2... although -qmin 1 is set.
Note that -qscale 1 works as expected and produce a correct stream (as 
far as I can see)
Tried a lot of options, but can't get ffmpeg to use q=1 when bitrate 
control is used.
Is there any reason for that behaviour ?

Command line :
ffmpeg -vstats_file NOQ1.log -i "processor_burning.avi" -y -g 15 -qmin 1 
-bf 2 -b 80000k -vcodec mpeg2video -f mpeg2video out.m2v
( source file is from 
ftp://upload.mplayerhq.hu/MPlayer/samples/avi/processor_burning.avi , 
and it is NOT a hd source, but problem is the same )

Thanks for your support.
Chris.

Log output (FFmpeg version SVN-r10908) :
...
frame=   100 q= 2.0 f_size=    335 s_size=       37kB time= 4.000 br=    
67.0kbits/s avg_br=    75.8kbits/s type= P
frame=   101 q= 2.5 f_size=    189 s_size=       37kB time= 4.040 br=    
37.8kbits/s avg_br=    75.4kbits/s type= B
frame=   102 q= 2.5 f_size=    189 s_size=       37kB time= 4.080 br=    
37.8kbits/s avg_br=    75.0kbits/s type= B
frame=   103 q= 2.0 f_size=   3298 s_size=       41kB time= 4.120 br=   
659.6kbits/s avg_br=    80.7kbits/s type= P
frame=   104 q= 2.5 f_size=    405 s_size=       41kB time= 4.160 br=    
81.0kbits/s avg_br=    80.7kbits/s type= B
frame=   200 q= 2.5 f_size=    180 s_size=       41kB time= 8.000 br=    
36.0kbits/s avg_br=    42.2kbits/s type= B
frame=   201 q= 2.5 f_size=    180 s_size=       41kB time= 8.040 br=    
36.0kbits/s avg_br=    42.1kbits/s type= B
frame=   202 q= 2.0 f_size=   3894 s_size=       45kB time= 8.080 br=   
778.8kbits/s avg_br=    45.8kbits/s type= P
frame=   203 q= 2.5 f_size=    199 s_size=       45kB time= 8.120 br=    
39.8kbits/s avg_br=    45.7kbits/s type= B
frame=   204 q= 2.5 f_size=    314 s_size=       46kB time= 8.160 br=    
62.8kbits/s avg_br=    45.8kbits/s type= B
frame=   205 q= 2.0 f_size=   4919 s_size=       50kB time= 8.200 br=   
983.8kbits/s avg_br=    50.4kbits/s type= P
frame=   206 q= 2.5 f_size=   1178 s_size=       52kB time= 8.240 br=   
235.6kbits/s avg_br=    51.3kbits/s type= B
frame=   207 q= 2.5 f_size=   2056 s_size=       54kB time= 8.280 br=   
411.2kbits/s avg_br=    53.0kbits/s type= B
frame=   208 q= 2.0 f_size=   7852 s_size=       61kB time= 8.320 br=  
1570.4kbits/s avg_br=    60.3kbits/s type= P
frame=   209 q= 2.5 f_size=   3070 s_size=       64kB time= 8.360 br=   
614.0kbits/s avg_br=    63.0kbits/s type= B
frame=   210 q= 2.5 f_size=   4822 s_size=       69kB time= 8.400 br=   
964.4kbits/s avg_br=    67.3kbits/s type= B
frame=   211 q= 1.6 f_size=  23453 s_size=       92kB time= 8.440 br=  
4690.6kbits/s avg_br=    89.2kbits/s type= I
frame=   212 q= 2.5 f_size=   6041 s_size=       98kB time= 8.480 br=  
1208.2kbits/s avg_br=    94.5kbits/s type= B
frame=   213 q= 2.5 f_size=   7198 s_size=      105kB time= 8.520 br=  
1439.6kbits/s avg_br=   100.8kbits/s type= B
frame=   214 q= 2.0 f_size=  16396 s_size=      121kB time= 8.560 br=  
3279.2kbits/s avg_br=   115.6kbits/s type= P
frame=   215 q= 2.5 f_size=   8108 s_size=      129kB time= 8.600 br=  
1621.6kbits/s avg_br=   122.6kbits/s type= B
...