[Theora-dev] Encoding paramaters...
Sat Jul 3 09:09:14 PDT 2004
>>>>> "illiminable" == illiminable <ogg at illiminable.com> writes:
> These are the defaults i'm using...
> mTheoraInfo.target_bitrate=400000; mTheoraInfo.quality=30;
> mTheoraInfo.dropframes_p=0; mTheoraInfo.quick_p=1;
> mTheoraInfo.keyframe_auto_p=1; mTheoraInfo.keyframe_frequency=64;
> mTheoraInfo.keyframe_mindistance=8; mTheoraInfo.noise_sensitivity=1;
There's another parameter, that's also not used in encoder_example:
sharpness. I played around with it a litte (by hacking
encoder_example.c) and it seems, that it's reverse. Valid values are 0,
1 and 2. If set to zero (the default), images are sharpest, but there
are artifacts (ringing?) around sharp edges, which seems to be a problem
for encoding high-quality anime (with lots of fine, sharp lines).
I set this to `2' now, and the result for "Chihiro" looks much better.
I get an artifact-free video with resolution 640x448 at quality `-v 5'.
After some tests, the average bitrate seems to be less than 550 kbps.
Note that I also set keyframe_frequency_force to 512. BTW from a look
at `toplevel.c' it is somewhat unclear to me, how `keyframe_frequency'
is interpreted, when `keyframe_auto_p' is 1. In that case
`keyframe_frequency_force' is used for keyframe generation, and
`keyframe_frequency' is only used for some kind of bitrate estimation.
Note that for a given quality, high values of `sharpness' also make
bitrate drop by quite some amount, so that for the same bitrate, an
actually higher quality should be selected.
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