[FFmpeg-devel] [PATCH] handle EAGAIN case in ffmpeg.c

[Benoit Fouet]

Luca Abeni wrote:
> Hi Benoit,
>
> Benoit Fouet wrote:
> [...]
>   
>>>> what i'm trying to do is having v4l2 working
>>>>     
>>>>         
>>> Unless something broke in the last two or three weeks, v4l2 should be 
>>> already working... What's the problem you are seeing?
>>>   
>>>       
>> shouldn't the DQBUF return EAGAIN when it has no frame available ?
>>     
>
> According to my understanding of the v4l2 specification, EAGAIN is only 
> returned if the video device has been opened using the O_NONBLOCK flag.
>
> [...]
>   
>>> The way is currently works is that the v4l2 input format blocks until 
>>> there is an available frame (unless you specify the 
>>> AVFMT_FLAG_NONBLOCK... In that case you have to modify ffmpeg.c)
>>>
>>>   
>>>       
>> i thought the DQBUF was always a non blocking ioctl, isn't it the case ?
>>     
>
> According to
> http://www.linuxtv.org/downloads/video4linux/API/V4L2_API/spec-single/v4l2.html#VIDIOC-QBUF
> (which should be the authoritative reference, I think)
> "By default VIDIOC_DQBUF blocks when no buffer is in the outgoing queue. 
> When the O_NONBLOCK flag was given to the open() function, VIDIOC_DQBUF 
> returns immediately with an EAGAIN error code when no buffer is available."
> So, the current code should be ok... As I said, it worked fine last time 
> I tested it :)
>   

ok, i'll check the driver then :)

> What's the behaviour you see when you try to capture video with ffmpeg? 
> Which capture card (and drivers) are you using?
>
>   

not standard ones but ours, so i'll check them ;)
thanks Luca

-- 
Ben
Purple Labs S.A.
www.purplelabs.com