[vlc-devel] [rms at gnu.org: VLC and V4L2]

Richard Hosking richard at hovis.net
Thu Oct 4 14:03:34 CEST 2007

The capture example is in the public domain... here
is the working url!:-


this is linked from the home page:-


I'm pretty sure the line of code calling free is
correct in the v4l2.c file as the manufacturer
of my v4l2 device has admitted they have an issue
inside their driver when closing and are fast
working on a fix for us.

So I would like to wait at least a week until this
is done so I can verify that the code in v4l2.c is
calling the closing operations correctly.


Rafaël Carré wrote:
> Hash: SHA1
> Richard Hosking a écrit :
>> I have more or less completed this.  Only mjpeg support
>> and testing with a device which has a tuner I cannot do
>> as my v4l2 device does not support this.
> Maybe the FSF can help here, providing you such a device ?
> I have no idea how much it costs.
>> Currently the v4l2 device I have has a bug in its drivers
>> which crashes when the device is closed. I am waiting for
>> the manufacturer to fix this fault (hopefully the end of
>> next week).  When they do this I will be able to test
>> that the calling code works properly before submitting my
>> v4l2.c file for hopeful inclusion into the trunk :-)
> :)
>> About 50% of the additions are taken from the reference
>> v4l2 capture program at http://v4l2spec.bytesex.org/spec/a14009.htm
>> (which I have cited), and about 30% is from the v4l.c
>> program, and the rest is me.
> The reference capture program is 404 for me, is it in the public domain,
> or has a special licence ?
>> I would rather wait until I can verify that the bug I
>> have is fixed before submitting my v4l2.c patch, but if
>> anyone wishes to see the current code it is here:-
>> http://hovis.net/v4l2.c
>> (line 651 is the call which is causing my device to
>> segfault at the moment)
> Seems odd, did you verify you were not overflowing ?
>> Richard.
> Thanks
>> Benjamin Pracht wrote:
>>> I would welcome any comment on this. I guess what we really lack here is
>>> a developer willing to spend some time on it. Does anybody see anything
>>> concrete the FSF can do to help? I remember some emails on this mailing
>>> list about some people working on the v4l2 module. Did we get any feedback?
>>> Writing a full support for all the v4l2 compatible devices might be a
>>> rather big work, but even a basic support of some devices would be a
>>> very nice first step.
>>> Currently, the v4l2.c file only contains probing code. I'm not even sure
>>> we really want to keep it. The pvr module probably also have useful
>>> code for the access part.
>>> What remains to be done is mostly:
>>> - to split the module in an access and an access_demux
>>> - complete the probing code
>>> - write device selection, device configuration code (source, tuner 
>>>   properties, v4l chroma to vlc FOURCC currespondance, etc)
>>> - write the data reading routines (some devices use read calls on the
>>>   device node, some use ioctls)
>>> - callbacks usable from a gui to get the device list (see direct show)
>>> - probably lots of other things I forget. I worked on those more than 1
>>>   year ago, not exactly sure anymore about how all this works.
>>> I'm afraid I won't be able to take this over. I can try to help anybody
>>> having questions on the existing code, but again, it's not much and I
>>> don't think there is a lot to say about it.
>>> ------------------------------------------------------------------------
>>> Subject:
>>> VLC and V4L2
>>> From:
>>> Richard Stallman <rms at gnu.org>
>>> Date:
>>> Sat, 29 Sep 2007 23:04:08 -0400
>>> To:
>>> bigben at videolan.org
>>> To:
>>> bigben at videolan.org
>>> I would really like VLC to work with V4L2, so I wonder: is there
>>> anything the FSF could do to help you make progress on this?  Please
>>> tell me what would be useful.
> - --
> Rafaël Carré
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