On Saturday 14 February 2009 19:58:08 Mauro Carvalho Chehab wrote:
>
> Hans and Andy,
>
> I understand that this have low priority. The only practical usage is if
> someone wants to do a better encoding for some video above the limits
> that cx2341x provides (for example, encoding with the same rate, but with
> MPEG 4, to have a higher quality).
>
> What I'm trying to say is that I don't see much value to change libv4l2
> to support read() method and HM12, since using read() method for a stream
> without a metadata doesn't work very well (sync issues, etc), but this is
> just my 2 cents.
The core issue is that libv4l2 shouldn't attempt to use mmap() with read()
if the driver doesn't support mmap(). If that's fixed, then I'm happy. I
think it's a simple thing for Hans to fix. If he doesn't have the time for
that, then I can take a look as well since I'd like to get the HM12
converter merged. It's handy for testing with qv4l2.
> With respect with ivtv-alsa and cx18-alsa, I think that, once having the
> driver ported to videobuf, it shouldn't be hard to use cx88-alsa as a
> reference for writing those drivers.
>
> About the efforts to port it, only you can evaluate it. In the case of
> em28xx, once having a videobuf driver for usb, it weren't hard to port it
> to videobuf (almost all troubles we had were related to the usage of a
> new videobuf module - videobuf-vmalloc). The resulting code worked a way
> better than the original driver and it is now easier to understand what
> it is doing at the videobuffers than what it used to be.
Just to be clear, if I would start out now creating the driver I would base
it around videobuf. Or if we had problems with the DMA and buffering, I
would probably choose to move to videobuf as well. But we have two stable
drivers and no user demand to implement videobuf/alsa. Everyone uses the
MPEG stream, and using streaming I/O to get the MPEG stream just makes no
sense. The read() call is the natural way to access MPEG data.
Given a choice between working on the v4l2_device/v4l2_subdev conversion and
upgrading V4L1 drivers to V4L2, or implementing videobuf/alsa in cx18/ivtv,
then it is clear that the first is a much more important use of my time.
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG
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