[Bug 729307] New: vtenc_h264: bitrate is very wrong

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=729307
  GStreamer | gst-plugins-bad | git

           Summary: vtenc_h264: bitrate is very wrong
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Mac OS
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: robert.swain at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


It looks like perhaps the bitrate parameter should be bits per second instead
of kilobits per second though it's not clear.

gst-launch-1.0 -ev videotestsrc num-buffers=1500 ! \
    video/x-raw,width=640,height=360,framerate=15/1 ! \
    timeoverlay ! vtenc_h264 bitrate=768 ! h264parse ! \
    mp4mux ! filesink location=test.mp4

The above would give 100s of video. It encodes in about 14s which is nice. The
resulting file size is: 1380225 bytes which works out as 110kbps. Nowhere near
768000.

If I run it with bitrate=768000, the resulting file size is: 22373189 bytes
which works out as 1.8Mbps, which is also way off.

I was curious whether the noise in the default smpte pattern was screwing the
rate control when using bitrate=768000 so I tried also one of the easier
patterns, 'ball'. That gave a file 837721 bytes large which works out as
67kbps.

For something possibly more realistic, I captured two minutes of what should
have been 720p30 from the FaceTime HD camera in this current model 13" Retina
MacBook Pro with bitrate=3000000 and I got 9Mbps. With bitrate=3000 I got
0.59Mbps with really awful quality.

Now, that camera is quite noisy and the framerate is very sensitive to dropping
if you're not in really bright lighting conditions. But even so, it seems like
something is wacky with the bitrate of this H264 encoder.

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