[vlc-devel] Kasenna GET_PARAMETER support
glen at lincor.com
Thu Nov 10 19:35:57 CET 2005
This is a somewhat hacky utilization of a potentially very useful
feature. But I thought I'd throw it out here for some feedback on how
best to do it correctly (Derk-jan and I spoke about it briefly but I was
under too much time pressure to do what he really wanted, so now's the
chance to get it right!!).
Kasenna has a GET_PARAMETER capability that I've enabled via liveMedia
(patch accepted on 2005.10.23). If you pass in a string "position" the
Kaenna will return position: <time> where time is the current time index
in seconds of the stream.
I've added an rc interface to this "server_position". Passing that in
will trigger some callbacks and get the request sent and result
recieved. Originally I'd it doing the return path properly with
callbacks once the server responded. However, due to the nature of our
application wrapping the rc interface to control vlc, it was easier to
have the rc command not return until the value changed or a timeout
happened. So that's why there's a not very nice while/usleep loop in
there. Very specific to our usage.
The capability is also put to use in the SET_RATE capability added by my
previous trickplay patch. After the pause happens, but before the play
with scale value, I get the current position from the server and use
that as the npt start time.
Derk-Jan suggested setting the pcr values so that GET_TIME returns an
accurate value. Currently it always seems to return 0 (as he explained,
the UDP data has no timestamps, so the pts that liveMedia gives over is
always 0). GET_TIME however is called in quite a tight loop, so only
periodically updating the value is advisable. I did have this working
and updating the pcr's every 10 seconds or so. The values seemed to get
out sync badly though and I didn't have time to resolve it. I'll try and
get to this shortly as it wasn't much of a change.
Glen Gray <glen at lincor.com> Digital Depot, Thomas Street
Senior Software Engineer Dublin 8, Ireland
Lincor Solutions Ltd. Ph: +353 (0) 1 4893682
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