There is new patch. With this patch you can recalculate bandwith for jpeg stream. See my post in list and try it: [patch] jpeg compression hacks. Tester are welcome!!!
On Fr, 2011-03-11 at 10:38 +0000, Paulo Assis wrote: > Hi, > > 2011/3/11 Alexey Fisher <bug-tr...@fisher-privat.net>: > > Raw stream is "simple", for example YUYV need 16 bits to describe one > > pixel. No extra action is done on this stream. Even if the camera lie > > about it setting, we can still calculate it our self. For example if you > > use YUYV 640x480 with 30 fps: > > 640×480×16=4915200 bit or 4915200/8=614400 byte > > so dwMaxVideoFrameSize=614400. > > > > Same value you will get if you check lsusb -vd xxxx:xxxx > > > > To calculate bandwidth uvc use framerate. This value deiced, can you or > > not use your webcam with some particular settings on your usb hub. > > > > Compressed stream can use different compression algorithms, most populas > > is jpeg. Compression depend on texture what your cam capture, and on the > > time it has for compression. For example if camera forced to push 30fps, > > it will choice speed against compression rate. > > actually it can also only send a part of the sensor image, just try > any of the logitech HD models, > when you pick a different frame rate (even for the same resolution) > you will get a very different image (more or less zoomed), > The compression ration seems more or less the same (at least the > quantization tables don't seem to alter). > > > > > With compressed stream we can't say for sure, how match bandwidth do we > > need. On cam's i tested it variate between 6% and 30% of uncompressed > > stream. If you provide wrong bandwidth to the cam, it will just freeze > > or send you black frame. > > Yes but you can decide on a maximum (say 40% :D) that is never > reached, this is better than allocating 100% of the bandwidth and can > be the difference between a working camera and a non working one. > > > > > So, manufacture should provide correct settings and they are different > > for each cam. > > I totally agree with this, but unfortunately, this is not always the > case, hence the need for the quirks. > In fact the bandwidth settings should vary at least according to > resolution, but what wee see in some cases is that manufactures just > use the same value for every situation (laziness related maybe). > > > > > Or we should add new quirk setting, what adjust compression ratio too. > > But before, we need some test cases, to find worts compression ratio, > > and add statistic collection to the driver. > > V4l2 has jpeg compression related ioctls, Laurent event created a > patch for uvc, but for some reason it was never integrated, in fact I > add support for it in guvcview, but as I remember although the cameras > I tested seem to accepted it, it didn't really cause any change in the > compression ratio, so I doubt very much it would cause any on the > bandwidth settings. > > Regards, > Paulo > > > > > Am Freitag, den 11.03.2011, 00:35 +0200 schrieb Asmaa ElAssal: > >> Yes, sir, but I use another one. > >> I received that analysiz from someone on that site about that old > >> webcam. I want to understand the problem of that previous cam > >> Excuse me, Could you more explain "Compressed stream is not really > >> predictable" and it's different of the uncompressed format. > >> > >> On Thu, Mar 10, 2011 at 11:59 PM, Alexey Fisher > >> <bug-tr...@fisher-privat.net> wrote: > >> Compressed stream is not really predictable. Every camera can > >> act > >> differently, so my be it will brick more than fix. > >> > >> Do your camera need this quirk? > >> > >> Am Donnerstag, den 10.03.2011, 19:43 +0000 schrieb modysama: > >> > modysama <asmaa.elassal.student <at> pua.edu.eg> writes: > >> > > >> > > > >> > > Fixing bandwidth quirk is only works for uncompressed > >> stream > >> > the YUYV format, it doesn’t work for MJPG. > >> > > Why??need explain, please > >> > > _______________________________________________ > >> > > Linux-uvc-devel mailing list > >> > > Linux-uvc-devel <at> lists.berlios.de > >> > > https://lists.berlios.de/mailman/listinfo/linux-uvc-devel > >> > > > >> > > >> > > >> > > >> > > >> > _______________________________________________ > >> > Linux-uvc-devel mailing list > >> > Linux-uvc-devel@lists.berlios.de > >> > https://lists.berlios.de/mailman/listinfo/linux-uvc-devel > >> > >> -- > >> Regards, > >> Alexey > >> > >> > >> > >> > >> -- > >> Asmaa El-said Rashad > >> Pharos University of Alex > >> Computer Department > >> 5th year > >> > >> > >> > > > > > > _______________________________________________ > > Linux-uvc-devel mailing list > > Linux-uvc-devel@lists.berlios.de > > https://lists.berlios.de/mailman/listinfo/linux-uvc-devel > > -- Regards, Alexey _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
