[MPlayer-users] black and white DVD

[D Richard Felker III]

On Tue, Nov 04, 2003 at 01:17:00AM -0800, Corey Hickey wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> tarass at club-internet.fr wrote:
> >[Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> >Le 11/04/2003 05:22 AM, D Richard Felker III a joliment écrit :
> >
> >>Maybe, maybe not. There's certainly a (small) benefit in speed, since
> >>libavcodec can skip looking at the (relatively small) chroma planes
> >>entirely for encoding. As far as improving quality, it depends on your
> >>source material. If your source is properly encoded black&white movie,
> >>with absolutely nothing in the chroma planes, then it will make no
> >>difference. On the other hand, if your source has noise or slight
> >>coloration in the chroma planes, using the "gray" option will throw
> >>all that away, saving a few bits.
> >
> >
> >I tried the colour version 715305ko, the gray 715306 ko ?
> >
> 
> I don't think that necessarily means anything. Libavcodec (unless you
> specify constant quantizers) tries to maintain the requested bitrate, on
> average, for the whole file. There's a certain acceptable tolerance,
> however, which is by default 8000kBit and changeable with the vratetol
> parameter. Whenever you change an option, the ratecontrol ends up having
> something entirely different and the end result may be in a different
> part of the acceptable range.
> 
> Also, make sure you're using 2-pass encoding for best results.
> 
> What would be more interesting for comparison would be the PSNR, which
> is an objective measurement of how close the encoded video is to the
> source material (post-cropping/scaling/etc.). You'll have to encode each
> test again, but this time add :psnr to your lavcopts. Mencoder will
> print out a line like this at the end:
> PSNR: Y:41.64, Cb:44.20, Cr:45.00, All:42.42
> Tell us the PSNR lines for the second pass of each test (at least, I'm
> curious). :)

And only compare the luma PSNR! Of course the chroma PSNR will be very
bad when using "gray" if there's any data in the chroma planes to
begin with!! :)

Rich