Greetings,
I have two Microsoft LifeCam Cinema Cameras attached to a single system
(only one USB 2.0 controller). I have set trace=1024 on uvcvideo and find
that the driver allocates the same amount of bandwidth regardless of what I
specify for resolution, fps, or codec in ffmpeg, vlc, etc.
Example:
[r...@fedora11-test ~]# ffmpeg -f video4linux2 -s 1280x800 -r 30 -i
/dev/video1 -f m4v 2-1280-800-maxfps.m4v
FFmpeg version SVN-r20557-snapshot, Copyright (c) 2000-2009 Fabrice Bellard,
et al.
built on Nov 22 2009 01:51:55 with gcc 4.4.1 20090725 (Red Hat 4.4.1-2)
configuration: --prefix=/usr --libdir=/usr/lib --shlibdir=/usr/lib
--mandir=/usr/share/man --enable-shared --enable-gpl --enable-version3
--enable-nonfree --enable-postproc --enable-avfilter --enable-avfilter-lavf
--enable-pthreads --enable-x11grab --enable-vdpau --disable-avisynth
--enable-libdc1394 --enable-libdirac --enable-libfaac --enable-libfaad
--enable-libfaadbin --enable-libgsm --enable-libmp3lame --enable-libnut
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
--enable-libschroedinger --enable-libspeex --enable-libtheora
--enable-libvorbis --enable-libx264 --enable-libxvid --extra-cflags='-O2 -g
-pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m32 -march=i586 -mtune=generic
-fasynchronous-unwind-tables' --disable-stripping
libavutil 50. 4. 0 / 50. 4. 0
libavcodec 52.41. 0 / 52.41. 0
libavformat 52.39. 2 / 52.39. 2
libavdevice 52. 2. 0 / 52. 2. 0
libavfilter 1. 8. 0 / 1. 8. 0
libswscale 0. 7. 1 / 0. 7. 1
libpostproc 51. 2. 0 / 51. 2. 0
[video4linux2 @ 0x858a860][3]Capabilities: 4000001
Input #0, video4linux2, from '/dev/video1':
Duration: N/A, start: 1262673238.027945, bitrate: 491519 kb/s
Stream #0.0: Video: rawvideo, yuyv422, 1280x800, 491519 kb/s, 30 tbr,
1000k tbn, 30 tbc
Output #0, m4v, to '2-1280-800-maxfps.m4v':
Stream #0.0: Video: mpeg4, yuv420p, 1280x800, q=2-31, 200 kb/s, 90k tbn,
30 tbc
Stream mapping:
Stream #0.0 -> #0.0
Press [q] to stop encoding
frame= 147 fps= 30 q=31.0 Lsize= 356kB time=4.90 bitrate= 595.6kbits/s
video:356kB audio:0kB global headers:0kB muxing overhead 0.000000%
And from dmesg:
uvcvideo: Device requested 3072 B/frame bandwidth.
uvcvideo: Allocated 5 URB buffers of 32x3072 bytes each.
---
[r...@fedora11-test ~]# ffmpeg -f video4linux2 -s 640x480 -r 30 -i
/dev/video1 -f m4v 2-640x480.m4v
FFmpeg version SVN-r20557-snapshot, Copyright (c) 2000-2009 Fabrice Bellard,
et al.
built on Nov 22 2009 01:51:55 with gcc 4.4.1 20090725 (Red Hat 4.4.1-2)
configuration: --prefix=/usr --libdir=/usr/lib --shlibdir=/usr/lib
--mandir=/usr/share/man --enable-shared --enable-gpl --enable-version3
--enable-nonfree --enable-postproc --enable-avfilter --enable-avfilter-lavf
--enable-pthreads --enable-x11grab --enable-vdpau --disable-avisynth
--enable-libdc1394 --enable-libdirac --enable-libfaac --enable-libfaad
--enable-libfaadbin --enable-libgsm --enable-libmp3lame --enable-libnut
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
--enable-libschroedinger --enable-libspeex --enable-libtheora
--enable-libvorbis --enable-libx264 --enable-libxvid --extra-cflags='-O2 -g
-pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m32 -march=i586 -mtune=generic
-fasynchronous-unwind-tables' --disable-stripping
libavutil 50. 4. 0 / 50. 4. 0
libavcodec 52.41. 0 / 52.41. 0
libavformat 52.39. 2 / 52.39. 2
libavdevice 52. 2. 0 / 52. 2. 0
libavfilter 1. 8. 0 / 1. 8. 0
libswscale 0. 7. 1 / 0. 7. 1
libpostproc 51. 2. 0 / 51. 2. 0
[video4linux2 @ 0x9a15860][3]Capabilities: 4000001
Input #0, video4linux2, from '/dev/video1':
Duration: N/A, start: 1262673302.162194, bitrate: 147456 kb/s
Stream #0.0: Video: rawvideo, yuyv422, 640x480, 147456 kb/s, 30 tbr,
1000k tbn, 30 tbc
Output #0, m4v, to '2-640x480.m4v':
Stream #0.0: Video: mpeg4, yuv420p, 640x480, q=2-31, 200 kb/s, 90k tbn,
30 tbc
Stream mapping:
Stream #0.0 -> #0.0
Press [q] to stop encoding
frame= 152 fps= 30 q=5.2 Lsize= 347kB time=5.07 bitrate= 561.4kbits/s
video:347kB audio:0kB global headers:0kB muxing overhead 0.000000%
and from dmesg:
vcvideo: Device requested 3072 B/frame bandwidth.
uvcvideo: Allocated 5 URB buffers of 32x3072 bytes each.
----
I had planned on showing the example from dmesg of the same allocation when
using mencoder with --v4l2-chroma=mjpeg ; but unfortunately the machine is
remote and just died...
At any rate, if anyone can verify that this is the (in)correct behavior of
uvcvideo i would appreciate it (but I am under the impression it is not
supposed to work this way, and is supposed to allocate bandwidth based on
the input parameters). I would be happy to provide any debugging information
necessary.
Thanks in advance.
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