On Wed, 27 Oct 2004, Dik Takken wrote:
> I noticed something strange while playing with mpeg2enc. When I encode a
> sequence of frames to progressive mpeg2, the output quality is *much*
> better than when I encode the same image sequence to progressive mpeg2.
Something does not read properly in that paragraph. How can the
quality of "progressive mpeg2" be different than "progressive mpeg2"?
> It seems to me that something must be wrong here. I use these
> options for mpeg2enc:
>
> ... | mpeg2enc -f 8 -b 9500 -q 1 -a 3 -o output.m2v
Well - one thing that's wrong is using -q 1. Known, in some cases,
to suffer from DCT/iDCT overflow in the MMX/SSE code. Or are you
doing the encoding on an PPC system - the Altivec routines seem to
not have the same problem.
> When I have png2yuv interpret the frames as top field first interlaced, it
> produces a mpeg file of the same size, but there are many more compression
> artifacts. It looks like it has been encoded with -q 10 or something. Why
Ah, but are they compression artifacts or interlacing "artifacts"?
If you're viewing the output on a progressive (i.e. computer monitor)
display then interlaced data will look poor compared to progressive
data. I suspect playing it on an interlaced display such as a TV
will likely look different than on a computer monitor.
Not sure if this will help - it might - but adding "-I 0" for
progressive and "-I 1" for interlaced content might make a different
(doubt it, but worth a try ;))
Are you using the cvs version, the last release version (1.6.2) or
an older version?
I've not seen any compression artifacts on interlaced content - but then
"-q 3" is as low as I've used (usually -q 4 is sufficient).
Cheers,
Steven Schultz
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