On Sunday 08 February 2009 14:01:34 Jeff Campbell wrote:
> > > "Variable and constant bit rate up to 15 Mb/sec" under Features and
> > > Benefits / Video Encoding
> > >
> > > At the moment the cx18 still reports 27 Mbps as the max in v4l2-ctl
> > > -L, which I think is just a carry over from the earlier 15/16 chip.
> > > Just wanted to flag it before it slipped my mind.
> >
> > I put it low on the list, because mucking with those means more
> > regression testing than normal to make sure I didn't screw up the ivtv,
> > pvrusb2, cx88, or cx23885 drivers, as they all call out to those too
> > (IIRC).
>
> I suspected that might be the case, just wanted to mention it before I
> forgot.
>
> In a similar vein, we were doing some testing with VBR versus CBR last
> night and noticed that the current structure, which I believe is also
> carried over from ivtv, does not allow changing the bitrate on the fly.
> However, the chip does allow changing the bitrate on the fly, but
> changing that will also create regression issues potentially. However,
> that being said, I used to be able to change the BR on the fly with ivtv
> and some time in the last year or so it changed so you could not write
> that while the device was in use. Not sure why that was done, perhaps for
> a different device in the same family?
If I remember correctly I disabled it for ivtv after experimentation showed
that changing the bitrate while capturing would sometimes (always? Can't
remember...) result in a corrupt stream. At least the cx23415/6 seems to be
very sensitive to changes in the compression parameters or in the video
format coming from the video digitizer. Perhaps the cx23418 can handle that
better, but I have my doubts given that it has the some core hardware.
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG
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