On Sat, 9 Feb 2019, 06:49 Gyan <ffm...@gyani.pro wrote: > > > On 09-02-2019 02:26 AM, Carl Eugen Hoyos wrote: > > 2019-02-08 6:08 GMT+01:00, Gyan <ffm...@gyani.pro>: > >> > >> On 08-02-2019 03:31 AM, Carl Eugen Hoyos wrote: > >>> . > >>> No strong opinion here, I hadn't realized that -crf 0 only works with > >>> newer versions. > >>> > >>> Can you explain why crf alone has no effect and needs -b:v 0? > >>> Isn't this a bug both with libvpx and libaom? > >>> > >> With crf present but VBV params absent, VPX operates using a constrained > >> Q RC mode , where the target bitrate acts as a ceiling. Since acvodec > >> has a non-zero default -b of 200 kbps, this produces undesirable > >> effects. If set to 0, VPX switches to constant quality. > > Yes. > > This looks like a bug to me. > If there's a bug, it's in libav, in that, we can't signal when a value > is assigned by the user or via user-initiated logic, versus being > assigned as a default fallback. So it's a design conflict, and the > workaround has been long documented. > > Maybe just before the next major bump, a new field should be introduced > in AVOptions which registers if the field was populated at the behest of > the user. > >> I do see this block though, > >> > >> if (avctx->codec_id == AV_CODEC_ID_VP9 && ctx->lossless == 1) { > >> enccfg.rc_min_quantizer = > >> enccfg.rc_max_quantizer = 0; > >> } else { > >> if (avctx->qmin >= 0) > >> enccfg.rc_min_quantizer = avctx->qmin; > >> if (avctx->qmax >= 0) > >> enccfg.rc_max_quantizer = avctx->qmax; > >> } > >> > >> > >> Looks like the quantizer range is disabled only by using the deprecated > >> option, or has this changed? > > Is your question "Isn't 'lossless 1' necessary for lossless encoding"? > Yes. A quick glance at vpx HEAD indicates it is, although -qmin & -qmax > 0 should also work. > > >> Also, with libvpx v1.7.0-1758, I get different results for -crf 0 -b:v > >> 0 vs only -lossless 1, with the latter producing a slightly larger > >> file, and its result showing a slightly larger SSIM score. Although > >> neither produces a SSIM of 1, like libx264. Not truly lossless? > > Please provide your input sample. > I can reproduce the difference in result with > fate-suite/h264-conformance/src19td.IBP.264 > > although the `-lossless 1` encoding does return as lossless in SSIM. >
What ssim command did you use, and why use this over a hash muxer like framehash? I'm always on the lookout for losslessness verification methods. Best, Kieran _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel