[Bug 770221] rtponviftimestamp: Implement property "Immediate"

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=770221

--- Comment #5 from Joakim Johansson <Joakim.Johansson at axis.com> ---
The definition of D-bit according to the specification:

D:  1  bit.  Indicates  that  this  access  unit  follows  a  discontinuity  in
 transmission.  It  is  primarily used during reverse replay; the first packet
of each GOP has the D bit set since it does not chronologically follow the
previous packet in the data stream (see section 6.5).

So, primarily it is used for reversed replay where each GOP is not considered
to follow previous packet since it is played reversed.

And then is the special case in Chapter 6.9 defined with the Immediate Header
which is supposed to Cancel all previous stacked Play and set the D-bit, why
D-bit needs to be set in this case is not explained and it is not very clear
since it doesn't seems to be a discontinuity in this case.

I and Linus reads the specification as that D-bit shall be used to indicate a
discontinuity and for us is not these use cases discontinuity:

    - Initial Play
    - Seek

However, the use case Play, Pause (for example 1 minute), Play (with no range
header) contains a discontinuity but that use case is not either working. This
is not detected (currently) by the certification tool but we have reported that
problem in bugzilla #770133 with a proposed solution as well.

As you say, a flushing seek is always used and the discont flag is set, but
that flag is not used (or checked by the certification tool) but we do not know
if anyone is really using the D-bit flag (except for the certification tool).

Do you really think that Initial Play and a new Play triggered by a seek
operation is a discontinued stream where the D-bit flag shall be set?

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