theoraenc bitrate problems (with and without GES)

[amindfv at mailbox.org]

I'm using GES to create a video with an ogg container and a theora video stream. I find that setting a bitrate value for the theora stream results in a consistently low video quality.

I set the bitrate like so:

    GstPreset *preset;
    preset = GST_PRESET (gst_element_factory_make ("theoraenc", "theorapreset"));
    g_object_set (preset, "bitrate", 400000, NULL);
    gst_preset_save_preset (preset, "this_is_a_test");

And sure enough, in .local/share/gstreamer-1.0/presets/GstTheoraEnc.prs I see:

    [this_is_a_test]
    name=theorapreset
    parent="NULL"
    qos=false
    min-force-key-unit-interval=0
    bitrate=400000

etc.

Regardless of what I set this bitrate value to, however, the bitrate of the output file hovers around 390 kb/s. Before I had set a bitrate value at all, the bitrate of the output file was 1874 kb/s, and visibly much higher quality.

Part of this problem, I assume, is that "bitrate" and "quality" are mutually exclusive settings, so when "bitrate" isn't set the quality default (=48) roughly corresponds to the 1874 kb/s bitrate? But then why does the bitrate setting seem to be totally ignored when it's set?

I've tested without GES and encoding profiles, simply with a one-liner. For example:

    gst-launch-1.0 videotestsrc ! video/x-raw,width=1280,height=720 ! theoraenc bitrate=4000000 ! oggmux ! filesink location=/tmp/foo.ogg

This doesn't result in consistent ~390 kb/s like with GES, but it also doesn't result in the requested bitrate.

What's going on?

Any help with this would be very appreciated!

Thanks,
Tom