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. 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. So, manufacture should provide correct settings and they are different for each cam. 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. 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
