[Bug 739771] v4l2src allocator fails

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=739771
  GStreamer | gst-plugins-good | 1.4.4

--- Comment #8 from Nicolas Dufresne (stormer) <nicolas.dufresne at collabora.co.uk> 2014-11-10 16:41:12 UTC ---
(In reply to comment #7)
> 
> My understanding after going through the log files(I may be wrong), In 1.2.2
> buffer type is configured as MMAP and it is successful, but in 1.4.4
> GST_V4L2_ALLOCATOR_PROBE fails to probe allocator type MMAP and throws the
> following warning
> 
> v4l2allocator
> gstv4l2allocator.c:651:gst_v4l2_allocator_new:<v4l2src0:pool:src:allocator>
> Could not probe supported memory type, assuming MMAP is supported, this is
> expected for older drivers not  yet ported to videobuf2 framework.

We changed this into a warning to try and support older driver that does not
comply with the spec. Basically if a driver says it's streaming, then we assume
MMAP is supported. This partially fixed support for BTTV. About that, could you
run v4l2-compliance against your driver, that should tell us a bit more about
what it does not do right. You'll find this test in:

http://git.linuxtv.org/cgit.cgi/v4l-utils.git/

> 
>  >  1. Try and fix the format, tell me if it works, give me the trace if it
> doesn't.
>   Could you please elaborate on this. What you mean by format?? 
>   Attached log files are without any source code modification in 1.4.4.

That means try:
gst-launch-1.0 v4l2src | video/x-raw,width=720,height=576 | checksumsink

And tell me if it works or not. Basically, what the driver seems to do wrong is
that it does implement frame size enumeration, but not the frame period. We
could hack around by looking at the chosen video standard, but it's a totally
unreliable method, since implementing video standard is optional.


> 
>  About the device driver.
>  Device driver supports videobuf2. I am collecting additional data on this.

Good, normally when we hit such a broken driver, I normally look at the driver
code to figure-out, but this one is of unknown source to me.

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