Clock selection and slave hardware clock

[Arnaud Vrac]

Hi all,

I have two problems related to the clock in my pipeline which includes
hardware accelerated elements:

1/ I cannot slave the clock provided by the hardware renderer element
to the system clock, because of GstClock limitations. The clock
adjustment algorithm only applies an offset to the time returned by
gst_clock_get_time, so this offset is effective when the hardware
driver uses its clock directly. Instead it would be nice if GstClock
could adjust the hardware clock frequency directly to match the master
clock.

2/ When using playbin and playing an RTSP stream, the system clock
provided by the rtpbin is selected instead of the clock provided by
the hardware renderer. This cannot work because the hardware clock
cannot be slaved to the system clock. The hardware renderer explicitly
refuses the system clock but it is still used anyway.

This works:
gst-launch rtspsrc location=rtsp://... ! rtpdepay ! hwaudiosink

This fails:
gst-launch playbin2 uri=rtsp://...

In the first case the hwaudiosink already is added to the pipeline
when the clock selection algorithm is run, so it is the one that is
selected. When using playbin the pipeline is already playing when the
audio sink is added, and the clock is not selected again when the
audio sink refuses the system clock.

Please tell me if it is possible to fix this and how.

Thanks !

-- 
Arnaud Vrac