> > On Thu, 27 Oct 2016, Francois Gouget wrote: > > > When uncapped x264enc can compress the frames beyond recognition in low > > bitrate situation. Beyond the set limit the gains are modest and it is > > better to drop frames to reduce the bit rate further. > > In case anyone is interested, here is a spreadsheet and graphs > of the frame sizes at various quantizer settings for h264 and VP8. > > http://fgouget.free.fr/tmp/Spice-qpmax-h264.png > http://fgouget.free.fr/tmp/Spice-qpmax-vp8.png > > http://fgouget.free.fr/tmp/Spice-qpmax.xls > > In both cases I did the test by setting the min and max quantizer to the > same value, tracing the frame size in encode_frame() and playing the > same test video. For instance: > > - gstenc_opts = g_strdup("byte-stream=true aud=true qp-min=15 > qp-max=35 tune=4 sliced-threads=true speed-preset=ultrafast > intra-refresh=true"); > + gstenc_opts = g_strdup("byte-stream=true aud=true qp-min=35 > qp-max=35 tune=4 sliced-threads=true speed-preset=ultrafast > intra-refresh=true"); > Which tool did you used ? Some printf on the code ? gst-launch ? > > In my tests a quantizer of 35 in x264enc is roughly equivalent to a > quantizer of 55 or 60 in vp8enc. The comparison is tricky because at low > bitrates x264enc tends to result in images that look noisy while vp8enc > instead tends to erase all details (e.g. you lose most of a face's > features). > Equivalent you mean looking at byte rate or quality ? > So it's interesting that at these settings vp8enc beats x264enc handily > in frame sizes: 1612 down to 984 bytes for vp8enc vs. 5048 to 1715 bytes > for x264enc. So if you want video on a very low bandwidth link vp8enc > seems to be the way to go. > > Also whereas at its maximum setting, 63, vp8enc still produces a poor > quality but still watchable video, at 40 x264enc produces video that's > annoying to watch and increasing the quantizer a bit more soon produces > unrecognizable images. This is why I don't plan on limiting the > quantizer for vp8enc. > I think some of these consideration should go on the commit message. I think you are right to limit the quantizer value and prefer to drop frames. Frediano _______________________________________________ Spice-devel mailing list Spice-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/spice-devel
