David, thanks for the reply.
On Thu, March 17, 2011 9:36:24 PM David Schleef wrote:
> Low delay works here, with both 4:2:2 and 4:4:4, using GStreamer:
Unfortunately GStreamer (from git) isn't close to configuring and
building under Cygwin...at least on my system.
Other than the flashing noise component (see previous email for sample)
ffmpeg 4:2:2 produces near-valid data. PSNR measurments indicate that
4:4:4 luma is fine, but chroma is a smeared mess. This may be the
"comet" artifact you mention.
> Possible reasons it's not working for you: Orc is generating bad code
> (sometimes happens, although pretty infrequently these days). You
> can test this by running the testsuite (make check), and/or running
> your code using ORC_CODE=backup in the environment.
make check output says "All 8 tests passed" however these two failures
were recorded:
cogorc_resample_horiz_1tap:
backup function : PASSED
compiled function: COMPILE FAILED
cogorc_resample_horiz_2tap:
backup function : PASSED
compiled function: COMPILE FAILED
Rerunning the ffmpeg tests with ORC_CODE=backup produces identical
output (i.e. the noise artifact is still present).
> Another possible reason, if you're seeing diagonal "comets", is that
> the transform-depth is changed away from the default. This is a bad
> idea.
I have seen the "comets" effect appear at certain compression ratios
then not be there at slightly higher and lower ratios. I haven't made
any explicit attempt to modify transform-depth. The minimal changes
I've made are in libavcodec/libschroedingerenc.c libschroedinger_encode_init():
schro_encoder_setting_set_double(p_schro_params->encoder,
"gop_structure", SCHRO_ENCODER_GOP_INTRA_ONLY);
schro_encoder_setting_set_double(p_schro_params->encoder,
"enable_noarith", 1);
schro_encoder_setting_set_double(p_schro_params->encoder,
"rate_control", SCHRO_ENCODER_RATE_CONTROL_LOW_DELAY);
schro_encoder_setting_set_double(p_schro_params->encoder,
"bitrate", avccontext->bit_rate);
(I'm assuming the first two are redundant.)
> As a side note, low delay profile is very sensitive to the values of
> horiz-slices and vert-slices. These should be factors of (width/16)
> and (height/8), which pretty much means 120 and 135.
The sample footage linked in my earlier email is 1920x1080.
Regards,
Stacey
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