[gstreamer-bugs] [Bug 632861] New: [x264enc] really bad quality with tune=zerolatency

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=632861
  GStreamer | gst-plugins-ugly | git

           Summary: [x264enc] really bad quality with tune=zerolatency
    Classification: Desktop
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: blocker
          Priority: Normal
         Component: gst-plugins-ugly
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: t.i.m at zen.co.uk
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


This has really bad quality (with libx264-104, svn20100918-0.2 and -ugly git):

  gst-launch-0.10 v4l2src ! video/x-raw-yuv,width=320,height=240 ! x264enc
tune=zerolatency byte- stream=false ! ffdec_h264 ! ffmpegcolorspace !
ximagesink sync=false

<robswain> tpm: it was due to a bug in x264enc
<robswain> zerolatency disables vfr which then made x264 use some different
parameters from its api for rate control
<robswain> iirc it used the timebase instead or something
<robswain> and we set the timebase to be 1/1000000000
<robswain> and i think x264 was ignoring the timestamps and just using frames
or something
<robswain> i did make a patch somewhere...
<robswain> http://people.collabora.co.uk/~robswain/x264_timebase_fix.patch
<robswain> try with that
<robswain> maybe it's not totally safe as the fps fraction isn't always
something useful
<tpm> robswain, that makes it work
<robswain> good good
<robswain> don't commit it yet
<robswain> i think perhaps there should be a check for the framerate from the
caps being 0/1
<robswain> as that would result in a timebase of 1/0 in this case and probably
screw everything up
<robswain> not to mention that 0/1 means variable which isn't allowed when that
b_vfr_blah isn't set
<robswain> so i'll add a check for that and error out if it occurs
<tpm> sounds like a plan
<robswain> other than that i think it should be ok
<robswain> however, perhaps it will break encoding for libx264 [after] the bug
was fixed...

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