mirror of https://github.com/mpv-player/mpv
91 lines
3.4 KiB
Plaintext
91 lines
3.4 KiB
Plaintext
HOW TO TEST SNOW
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Snow is an experimental wavelet-based codec made by the FFmpeg developers,
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and while it is still in heavy development, it is already giving very good
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results.
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Be very careful though, as the format of the bitstream produced might
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change, do not rely on it to store videos that you value.
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For this reason, MEncoder will not encode without 'vstrict=-2' on the
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command line.
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OPTIONS RECOGNIZED BY SNOW
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* vqscale=<0.0-255.0>
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Encoding quality, sane range 1-10. 0 is lossless.
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May be fractional.
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A given quality in snow needs a somewhat lower qscale than the same
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quality in MPEG-4.
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* vpass=<1-3>
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Activates internal two (or more) pass mode.
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* vbitrate=<value>
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Specify bitrate of 1pass CBR or 2pass ABR. default: 800 kbit/s.
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This is not very accurate for short videos.
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* lmin, lmax, vqcomp, vratetol, vrc_eq, vrc_override
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Generic multipass ratecontrol options, subject to the same suggestions
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as in other codecs.
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lmin=1 can be useful for medium to high bitrates (see vqscale).
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* cmp, subcmp, mbcmp
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Set the comparison function, default: 0 (SAD).
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useful values = 0 (SAD), 1 (SSD), 2 (SATD),
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11 (5/3 wavelet), 12 (9/7 wavelet).
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SAD is fastest and lowest quality.
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SSD is the only function that makes correct decisions about intra vs
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inter (mbcmp) when using fast motion estimation, but is not the best for
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the actual search (cmp, subcmp).
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The wavelet functions (use the one that matches pred) are best quality,
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especially with vme=8, but are very slow.
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SATD is a good balance.
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You can add 256 to any of the options to enable chroma motion
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estimation for that comparison (e.g. mbcmp=257 for SSD with chroma),
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but it doesn't seem to help much for the moment.
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* pred=<0-2>
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Wavelet type.
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0 = 9/7 wavelet, default.
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1 = 5/3 wavelet.
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2 = 13/7 wavelet.
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9/7 is probably better for for lossy coding, and 5/3 for lossless.
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NOTE: 9/7 wavelet doesn't work with lossless mode.
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* qpel
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Refines motion estimation, default: off.
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This setting always helps compressibility, but costs some CPU time
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both while encoding and decoding.
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* v4mv
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Allows smaller motion partitions, default: off.
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v4mv is theoretically good, but in practice isn't really working yet.
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The current MB decision algorithm doesn't make very good use of this:
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It improves quality, but also increases bitrate. (You could get
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more quality per bitrate by reducing quantizer instead.)
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* vme=<4|8>
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The default EPZS (4) is the same as in other formats.
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Snow also supports iterative motion estimation (8), which jointly
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optimizes adjacent blocks to make the most of OBMC. This significantly
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improves compression, but is very slow.
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Iterative ME currently does not perform scenecut detection, so should
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be used only in the second pass of a two pass encode.
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* refs=<1-8>
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Allows each block to choose which of several reference frames to
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motion compensate from. Default: 1. Larger values always improve
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compression, but cost lots of CPU-time when encoding and extra
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memory when decoding.
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In short:
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The best options in almost all cases are
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vcodec=snow:vstrict=-2:vpass=1:vbitrate=$B:pred=0:cmp=2:subcmp=2:mbcmp=1:qpel
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vcodec=snow:vstrict=-2:vpass=2:vbitrate=$B:pred=0:cmp=12:subcmp=12:mbcmp=1:qpel:vme=8:refs=8
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Decent, fast options are
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vcodec=snow:vstrict=-2:vpass=1:vbitrate=$B:pred=0:cmp=1:subcmp=1:mbcmp=1
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vcodec=snow:vstrict=-2:vpass=2:vbitrate=$B:pred=0:cmp=2:subcmp=2:mbcmp=1:refs=2
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