I'm transcoding MPEG-2 files into mpeg4 with mencoder. My 2-pass encoding command is:
mencoder INFILE -ovc lavc -lavcopts vcodec=mpeg4:vpass=1 -oac copy -o /dev/null
mencoder INFILE -ovc lavc -lavcopts codec=mpeg4:vbitrate=4000:mbd=2:trell:vpass=2 -oac copy -o OUTFILE
The source material is also 4 mbits/sec. The output file is noticeably worse quality than the input. Normally, I'd expect some loss in quality during transcoding, but this isn't during high-motion scenes. These are TV shows with lots of talking heads, and very little motion.
The problems are fairly small, and you wouldn't notice them with a casual glance. There's two types of artifacts:
1: Blocking: the transition from one block of video data to the next isn't seemless.
2: Color pallete problems: imagine the clear blue sky which changes the shade of blue from left to right. The change should be gradual, and not noticeable at any pixel. But you can clearly globs of the sky where the pixel values change suddenly from one area to the next.
The problems are subtle and not noticeable at a casual glance, but I'd like to fix it. Are there simple command-line options that can do that?
