On Mon, 15 Mar 2004 [EMAIL PROTECTED] wrote:
> Does the option "-R" used with mpeg2enc have
> any influence in the quality of the transcoded
> video stream? If I am not wrong, in old versions
> of mjpegtools the default is "-R 2" and in the
> latest one it is "-R 0", which speeds up processing.
-R simply specifies the number of B frames to place between I/P
frames. The special case of -R 0 means to disable B frames completely
_and_ by default use DPME (Dual Prime Motion Estimation).
NOTE: At least 1 hardware player and a couple software players do
not implement DP in their MPEG-2 decoders. There is now
an option to mpeg2enc called --no-dualprime-mpeg2 which can
be used when generating output for broken decoders.
Now for the real answer ;)
For very clean (miniDV/Digital8) sources B frames are ok, but if the
sources are analog (and thus likely to have noise) the B frames
take bits away from the P frames which effectively reduces the quality
of the encoded video. Even for high quality sources NOT using B
frames helps with high motion scenes.
In general I have found that not using B frames at all gives a lower
bitrate and better looking (to the eyeballs - I haven't run any
objective tests) output. The other benefit is that without having
to compute B frames the encoding runs faster ;)
Cheers,
Steven Schultz
p.s. For even better quality use -D 10. That also helps to reduce the
moving grey blocks effect.
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