On Sat, 14 Feb 2009 15:11:13 +0100 Hans Verkuil <hverk...@xs4all.nl> wrote:
> On Saturday 14 February 2009 15:05:14 Andy Walls wrote: > > On Sat, 2009-02-14 at 12:06 +0100, Hans Verkuil wrote: > > > On Saturday 14 February 2009 11:32:06 Mauro Carvalho Chehab wrote: > > > > On Sat, 14 Feb 2009 10:08:31 +0100 > > > > > > > > Hans Verkuil <hverk...@xs4all.nl> wrote: > > > > > On Saturday 14 February 2009 09:52:06 Mauro Carvalho Chehab wrote: > > > > > > On Fri, 13 Feb 2009 13:57:45 +0100 > > > > > > > > > > > > Hans Verkuil <hverk...@xs4all.nl> wrote: > > > > > > > Hi Hans, > > > > > > > > > > > > > > I've developed a converter for the HM12 format (produced by > > > > > > > Conexant MPEG encoders as used in the ivtv and cx18 drivers). > > > > > > > > > > > > > > But libv4l2 has a problem in its implementation of v4l2_read: > > > > > > > it assumes that the driver can always do streaming. However, > > > > > > > that is not the case for some drivers, including cx18 and ivtv. > > > > > > > These drivers only implement read() functionality and no > > > > > > > streaming. > > > > > > > > I suspect that the only two drivers that don't support mmap() are > > > > ivtv and cx18. All other drivers support it, including other drivers > > > > that also provides compressed data (like jpeg webcams). In a matter > > > > of fact, most applications work only with mmap() interface (being > > > > mythtv and mplayer capable of supporting both read() and mmap()). So, > > > > by providing mmap(), other applications will benefit of it. > > > > > > > > Also, there is a sort of chicken and egg trouble: almost nobody uses > > > > raw formats, since it uses a non-standard format that it is not > > > > supported by userspace apps. The libv4l2 is the proper way for > > > > handling it, but only works with mmap(). > > > > > > I'd be happy if libv4l2 would just check whether mmap is supported, and > > > if not then disable adding the extra pixelformats. That's easy to do > > > there, and would make it possible to add hm12 for use with > > > libv4lconvert. While it would be nice from my point of view if > > > libv4l2's read() could convert without using mmap, I have to agree that > > > that is probably overkill. > > > > > > And nobody really cares about raw video with ivtv and cx18. Really. > > > I've had perhaps 3-4 queries about this in all the years that I've been > > > maintaining ivtv. Anyway, it will only be useful if we also add a > > > proper alsa driver for the audio. > > > > > > Bottom line is: no time on my side and no pressure whatsoever from the > > > users of cx18 and ivtv. There are also additional complications with > > > respect to splicing the sliced VBI data into the MPEG stream that will > > > make a videobuf conversion much more complicated than you think. It > > > will mean a substantial and risky overhaul of the driver that requires > > > probably weeks of work. > > > > > > Yes, I do want to do this, but unless someone else steps in it won't be > > > anytime soon. > > > > I can convert cx18 if someone really cares, but *no one* has ever > > directly enquired about the YUV (HM12) data from cx18. (I think there > > was quite a long time when it actually may not have been wokring - > > nobody cared.) When someone has paid the extra money for the encoder > > hardware, raw formats are really just a nice to have. There is cheaper > > hardware for raw formats. > > > > Anyway, such a conversion to mmap and/or videobuf is very far down on my > > TODO list. Whatever I do for cx18 may not translate directly to usable > > code for ivtv, the buffer handling is slightly different and simpler > > since there's no MPEG decoder to worry about. > > > > Again, it's not impossible, just a matter of time and demand. I have > > little time and I have no demand, aside from Hans Verkuil's desire to > > get an HM12 converter into the library. > > > > I haven't done any research, but I'm surprised that no other supported > > chip offers this format. I guess maybe that has something to do with > > the CX23415's origins from Internext Compression Inc. > > It's a macroblock format where all Y and UV bytes are organized in 8x8 > blocks. I believe it is a by-product of the MPEG encoding process that is > made available by the firmware as a bonus feature. It is clearly meant as > the source format for the actual MPEG encoder. Pretty much specific to the > cx2341x devices. 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. 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. Cheers, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
