[Bug 776712] vaapih264enc doesn't output AU delimiters

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=776712

--- Comment #18 from Hyunjun Ko <zzoon at igalia.com> ---
(In reply to Víctor Manuel Jáquez Leal from comment #17)
> 
> Are these patches part of the spec??

No. It's just a kind of policy of encoder.

Basically, SPS and PPS are placed in the first Access unit mandatorily and
doesn't need to be placed any more under assumption that decoder got
sequence/picture parameters successfully.
But normally, they are inserted to the stream periodically for 2 reasons.
1\ A decoder sometimes needs to start decoding mid-stream.
2\ If the stream has been changed for some parameters, an encoder inserts
SPS/PPS again.

Currently, vaapi h264 encoder does this with the flag config_changed.
But in the case of this issue, hlssink produces seperated segment file (since
target-duration property is set to 1).
Meanwhile, hlssink sends GstForceKeyUnit event if the duration is expired and
about to start new segment file, which means when an encoder get this event,
it needs to refresh status of encoder and produce IDR(Instantaneous Decoding
Refresh) picture. This is what these patches are doing.

In addition, these patches also fix a kind of bug. Currently, if it gets
GstForceKeyUnit, sets to produce I-frame. But there's no changed config, so it
doesn't produce SPS but produces PPS, which is absolutely wrong.
This is exactly the failure of this issue.

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