[gst-devel] video playback fast (record with v4l2src)

[Jesse Lang]

Ronald,

Ronald S. Bultje wrote:

>Hi Edgar,
>
>On Tue, 19 Sep 2006, Edgard Lima wrote:
>  
>
>>For v4l2 drivers we can know the framerate using  VIDIOC_G_PARM
>>See how it works looking the function gst_v4l2src_get_fps (also copied
>>bellow) at
>>http://webcvs.freedesktop.org/gstreamer/gst-plugins-bad/sys/v4l2/v4l2src_calls.c?view=markup
>>
>>btw: I have two webcams here, just one those drivers implements
>>VIDIOC_G_PARM
>>    
>>
>
>For some purposes, indeed, VIDIOC_G_PARM works fine. However, as you said
>here, and as I know from practice, most webcams don't actually implement
>this. This is because there is no decent way to _set_ the framerate using
>this API. You have to understand that the get-methods are fine for TV
>cards, where the FPS depends on the norm, but not for webcams, where the
>FPS is a separate property and such a thing as norms don't exist.
>  
>
I for one am using a saa7134 card which supports norms and gets the 
correct framerate, and yet I am experiencing this problem.  Even if the 
framerate is not correct, I should think videorate should be able to 
correct it for use with AVI or any other container.

>Implementing it is thus practically worthless. The pwc driver implements
>the same flag-field-hack that they use in v4l1 also (through a private
>ioctl).
>
>  
>
>>Do you think those methods aren't enough? I mean, the v4l2 standard
>>should be improved or v4l2 drivers shoould?
>>    
>>
>
>API, I'm afraid, as explained above.
>
>  
>
>>....I'm afraid, does it mean we can't record A/V coming from rtp,
>>v4l[12], (live)? I think we should think about more robust way to do
>>that (would it be videoscale?).
>>    
>>
>
>Not into AVI, but fortunately, you won't do that anyway.
>
How should I capture both audio and video so that they sync?  I imagine 
it needs to be muxed in one form or another.   If AVI is not an option 
as you say, and OGG does not work either, what options are there?

> For RTP and live
>recording from v4l, you really want to think this whole system through.
>If you don't understand the responsibilities of each gst element, the
>drivers (API/implementations + issues/bugs) and such, I don't think you'll
>be able to write a solution that works very well. If it just works for pwc
>webcams when transcoding in ogg/rtp using some obscure gst-launch
>commandline, that's really good already, but you're really not there yet,
>you're just at the beginning.
>  
>

>Ronald
>
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