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2 commits

Author SHA1 Message Date
Mathieu Duponchelle
90f5ae8f45 ulpfecdec: output perfect seqnums
ULP FEC, as defined in RFC 5109, has the protected and protection
packets sharing the same ssrc, and a different payload type, and
implies rewriting the seqnums of the protected stream when encoding
the protection packets. This has the unfortunate drawback of not
being able to tell whether a lost packet was a protection packet.

rtpbasedepayload relies on gaps in the seqnums to set the DISCONT
flag on buffers it outputs. Before that commit, this created two
problems:

* The protection packets don't make it as far as the depayloader,
  which means it will mark buffers as DISCONT every time the previous
  packets were protected

* While we could work around the previous issue by looking at
  the protection packets ignored and dropped in rtpptdemux, we
  would still mark buffers as DISCONT when a FEC packet was lost,
  as we cannot know that it was indeed a FEC packet, even though
  this should have no impact on the decoding of the stream

With this commit, we consider that when using ULPFEC, gaps in
the seqnums are not a reliable indicator of whether buffers should
be marked as DISCONT or not, and thus rewrite the seqnums on
the decoding side as well to form a perfect sequence, this
obviously doesn't prevent the jitterbuffer from doing its job
as the ulpfec decoder is downstream from it.

https://bugzilla.gnome.org/show_bug.cgi?id=794909
2018-04-19 18:17:39 +02:00
Mikhail Fludkov
d5ad50bd61 rtp: Implement ULPFEC (RFC 5109)
We expose a set of new elements:

* ULPFEC encoder / decoder
* A storage element, which should be placed before jitterbuffers,
  and is used to store packets in order to attempt reconstruction
  after the jitterbuffer has sent PacketLost events
* RED encoder / decoder (RFC 2198), these are necessary to
  use FEC in webrtc, as browsers will propose and expect ulpfec
  packets to be wrapped in red packets

With contributions from:

Mathieu Duponchelle <mathieu@centricular.com>
Sebastian Dröge <sebastian@centricular.com>

https://bugzilla.gnome.org/show_bug.cgi?id=792696
2018-02-21 14:15:22 +01:00