[gst-devel] question about GstClock not set

[Julien Isorce]

2009/8/25 Wim Taymans <wim.taymans at gmail.com>

> On Tue, 2009-08-25 at 16:40 +0200, Julien Isorce wrote:
> > Hi,
> >
> > I attach to this mail a minimal test to provide a gstreamer behaviour
> > that I do not understand.
> >
> > Actually, I would like to know why the clock can be not set yet
> > whereas some buffers are dispatched.
> > I mean I put an identity element between a videotestsrc and a
> > fakesink,
> > and I am checking the clock availability in the identity handoff
> > callback.
> >
> > Why am I able to get raw video buffers from handoff callback whereas
> > no clock is set on identity yet ?
> > Moreover in this case the timestamp buffer is valid, but I assume this
> > timestamp was set by the internal clock.
> > I can understand that the internal clock was already there before
> > playing,
> > and I can also understand that the internal clock is affected on
> > elements only when going to playing state (or at least ready).
> > But I think the clock should be always available from a handoff
> > callback, at least if the buffer timestamp is valid.
> >
>
> The first buffer is part of preroll in PAUSED. It is only after all
> sinks receive a buffer that a clock is selected and the pipeline is set
> to PLAYING.


ok thx for the explanation.

In a more complex pipeline, it can take some times before all sinks receive
a buffer.
And so an element can receive a lot of buffers
before all elements received a buffer ?
I mean a lot of handoff calls with no access to the clock inside the
callback.
It could explain the behavior I have there in a use case.

Anyway, I assume i should consider the buffers only after that playing state
is reached.

Sincerely

Julien


>
>
> Wim
>
> > ( to compile the test: gcc -Wall $(pkg-config --cflags --libs
> > gstreamer-0.10) main.c -o main )
> >
> > (output:
> >
> > identity has clock: 0, timestamp is valid: 1
> > pipeline is now playing
> > new clock set from: pipeline
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > identity has clock: 1, timestamp is valid: 1
> > End of stream
> >
> > )
> >
> > Sincerely
> >
> > Julien
> >
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