FsAppTransmitter / dummy call in nullprpl

[David Woodhouse]

On Fri, 2018-02-02 at 13:31 +0000, David Woodhouse wrote:
> Before I do the step of faking RTP myself, I started with purely adding
> rtpopuspay/rtpopusdepay in my pipelines and switching to
> fsrtpconference. And now I'm back to "I am clueless and I don't know
> why this doesn't work mode" and asking for help again... :)

Some progress... attached are a couple of patches against the Pidgin
repository. The first adds fs-app-transmitter and a hack in the null
PRPL which makes a dummy call, and works basically like the code in my
Chime PRPL.

The second converts it to use RTP, and I can get it working with a
couple of hacks.

Firstly, I need to *remove* libgstsrtp.so from my system. Unless I do
that, it fails to work:

0:00:15.265806297  5308 0x5573bd72c830 DEBUG               GST_CAPS gstpad.c:2215:gst_pad_link_check_compatible_unlocked:<tee1:src_1> src caps application/x-srtp
0:00:15.265814903  5308 0x5573bd72c830 DEBUG               GST_CAPS gstpad.c:2217:gst_pad_link_check_compatible_unlocked:<valve1:sink> sink caps application/x-rtp, media=(string)audio, payload=(int)[ 96, 127 ], clock-rate=(int)48000, encoding-name=(string){ OPUS, X-GST-OPUS-DRAFT-SPITTKA-00 }
0:00:15.265878067  5308 0x5573bd72c830 INFO                GST_PADS gstpad.c:2464:gst_pad_link_full: link between tee1:src_1 and valve1:sink failed: no common format

Secondly, I have to upgrade to the latest farstream (I've been testing
on Ubuntu 16.04 with farstream 0.2.7). Unless I do that, I can't find
any way to make OPUS work. Whatever I've put in fs-codecs.conf and
whatever I've put in farstream-{send,recv}-profile properties, I
haven't managed to get it to succeed.

After I've solved those, I'll turn my attention to the fact that
although the nullprpl works with those caveats, I still haven't got my
own code with the "real" GstAppSrc/GstAppSink pipeline working. I get
outbound audio from my mic to the network, but I never see a farstream-
recv-codecs-changed message, and the inbound pipeline isn't set up.
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