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 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
