[Bug 776983] New: opusenc does not discard silence if DTX enabled

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=776983

            Bug ID: 776983
           Summary: opusenc does not discard silence if DTX enabled
    Classification: Platform
           Product: GStreamer
           Version: 1.10.x
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: andreas.kling at gmail.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

if dtx is enabled and silence is detected opusenc should only encode 1 frame
each 400ms, as stated in RFC 6716, 2.1.9.

in function gst_opus_enc_encode() 1 is returned from opus_multistream_encode(),
signaling the frame should be discarded cause of detected silence.
Each 400ms a value != 1 is returned from opus_multistream_encode().

I use the attached patch to discard the frame.
can you tell me why this might be a bad idea?

I use this pipeline for testing
gst-launch-1.0 pulsesrc ! "audio/x-raw,channels=1,rate=48000" ! opusenc
audio-type=2048 bandwidth=1103 bitrate=20000 bitrate-type=1 inband-fec=TRUE
packet-loss-percentage=1 dtx=TRUE ! fakesink

I came across this while measuring network bandwidth using opusenc with dtx and
rtpopuspay.
The packet rate was constant, one packet each 20ms.
There where packets containing only one single RTP payload byte.
With the attached patch the packet rate is irregular with a minimum of one
packet each 400ms, always containing multiple bytes.

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