Re: [Mjpeg-users] Compare yuvscaler and y4mscaler

[<ro...@ub...>]

On Sun, Jan 04, 2004 at 09:28:30AM -0800, Steven M. Schultz wrote:
> 
> On Sun, 4 Jan 2004 ro...@ub... wrote:
> 
> > How do y4mscaler and yuvscaler compare when scaling a video stream for MPEG2
> > encoding for SVCD, in terms of speed and image quality?
> 
> 	I've found y4mscaler to be better.  Depending on the scaling method
> 	chosen (and y4mscaler offers many to choose from) the speed can be
> 	very fast to fairly slow.   You have the choice of (and you can see
> 	this with 'y4mscaler -S option=help') linear, quadratic, cubic, 
> 	cubicCR, cubicB, and sinc:N (where you can choose how many taps are
> 	used - value of N is open to debate, the higher the value the slower
> 	the speed but higher quality - reasonable value is 4, I tend to use 8).

How does its speed compare to yuvscaler when encoding to
similar quality (it that is possible anyway)? I have been
using yuvscaler with the command line call:

  yuvscaler -v 0 -O SVCD -n n

as a filter. What would be the scaling method whose resulting
quality best aproximates to the yuvscaler call above?

> 
> 	The other thing I use y4mscaler for is the chroma space conversion -
> 	usually to go from 4:1:1 to 4:2:0 but I have on occasion used it to
> 	create 4:2:2 or 4:4:4 content for testing.

I do not know yet when a chroma space conversion is needed.
In fact, I have not yet studied about chroma space. I think
that for the processing I have done up to know it was not
needed. Is there a specific situation where chroma space
conversion is required?

> 	The presets are quite useful and do a good job of intuiting the
> 	correct proceedure. [...]

Do the presets set a good scaling method? Or should I worry
about learning them to choose one?

> 	Try it, I think you'll like it ;)

I am trying it with the following commands:

$ mkfifo -m 660 stream.yuv
$ mplayer -noframedrop -vo yuv4mpeg -nosound -v -osdlevel 0 \
    the.two.towers.avi -sub the.two.towers.srt -subpos 78 \
    -vf expand=:504
$ cat stream.yuv |
  y4mscaler -O preset=SVCD |
  mpeg2enc -v 0 -I 0 -s -f 5 -V 230 -S 800 -a 2 -F 1 -n n -4 2 -2 1 \
    -b 2800 -B 284 -q 6 -K FILE=matrix.txt -R 0 -E -11 \
    -o the.two.towers.m2v

But y4mscaler gives the messages:

   INFO: [y4mscaler] Input Stream Header:
   INFO: [y4mscaler] <<<   frame size:  672x504 pixels (508032 bytes)
   INFO: [y4mscaler] <<<   frame rate:  239759/10000 fps (~23.975900)
   INFO: [y4mscaler] <<<    interlace:  none/progressive
   INFO: [y4mscaler] <<< sample aspect ratio:  ?:?
**ERROR: [y4mscaler] Unknown norm; cannot determine SVCD format.

Adding the option "-I norm=NTSC" to the y4mscaler command line does
not help (the error message is the same from y4mscaler).

Any help?

Regards.

Romildo