[Bug 752962] v4l2videodec: Add resolution change support

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=752962

--- Comment #9 from Nicolas Dufresne (stormer) <nicolas.dufresne at collabora.co.uk> ---
(In reply to kevin from comment #8)
> For video decoder element input caps change, seems should be handled in
> gstvideodecoder base. Is it ok to file another ticket to implement?
> 
> This ticket only handle video decoder output change without set_caps ().
> Such as H264 in byte-stream format, the header change detect by video
> decoder.

I don't want half a renegotiation supported. If a demuxer spread the
width/height field in the encoded caps, you'll have a set_caps(), if it does
not, you won't. If you only implement one of these two, then renegotiation will
be half broken.


(In reply to kevin from comment #8)
> Which is the best indicator to indicate V4L2 user need check event. zero
> payload buffer, EPIPE or LAST flag? As dqevent () will be block call, will
> call dqevent () after got one indicator. I use zero payload buffer currently.

First rule, never let you program block on an ioctl() (Currently G_FMT(CAPTURE)
is the exception, and you might be about to remove it). Instead, you should
poll for read after registering the event. The code might need a little
refactoring. Having the poll buried in the buffer pool isn't ideal, I do have
plan for 1.7/1.8 to rewrite the queue handling in order to reduce the amount of
abstraction here.

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