[MPlayer-dev-eng] enhancement for yuv4mpeg output driver
xyzzy at speakeasy.org
Wed Jan 19 22:31:26 CET 2005
On Wed, 19 Jan 2005, Steven M. Schultz wrote:
> On Tue, 18 Jan 2005, Trent Piepho wrote:
> > floating point value (right?). The yuv4mpeg driver turns this into x/1000000,
> > e.g. 23.98 fps becomes 23975999/1000000
> That's been a PITA for eons - getting F29969999:1000000 instead of
I'm glad I'm not the only one it's been annoying.
> > mplayer has the wrong idea of the pixel aspect isself, for example, a 720x480
> > 4:3 NTSC DVD should be scaled to 720x528, not 720x540. So I added an 'aspect'
> The scaled size isn't placed in the yuv4mpeg2 header so I think that's
> a different issue (when playing the movie on the computer for example)
> but you're right, the wrong thing is being done.
> The SAR (sample aspect ratio) placed in the yuv4mpeg2 header
> should be 10:11 for "NTSC", and 59:54 for "PAL" (or 40:33 and 118:81
> for 16:9 movies in the two video systems). Hmmm, but when you're
> decoding a SVCD the SAR is 15:11 and 59:36 respectively). Does the
> yuv4mpeg module have sufficient knowledge to emit the correct 'A'
> tag? If not then "0:0" is appropriate.
I use mplayer's idea of the correct scaled size of the video to guess the
sample aspect ratio. In some cases this works, a 704x480 4:3 DVD will have
a SAR of 10:11, a HDTV capture will have a SAR of 1:1, etc. In some cases
it is sligtly off, due to pixel rounding. In others it is off by a bit more,
because mplayer has the wrong idea of the SAR itself.
> 720/540 is a 4/3 display image using square pixels (which is what
> computer displays use) so that's correct. Not sure how 528 was
> derived - how did you come up with 720x528 being a 4/3 display aspect?
Try it with mjpegtools, and it will be obvious. The sample aspect ratio of a
720x480 DVD is 10:11, yes? So make yourself a 720x480 A10:11 y4m file with
mplayer and my patch or y4mcolorbars or something. Now scale it with
yuvscaler -O SIZE_720x540, then again with yuvscaler -O SIZE_720x528. Which
one gives an output sample aspect ratio of 1:1?
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