On Fri, 11 Sep 2020, Moritz Barsnick wrote:
ffmpeg has several display output muxers/devices. The most common one
(saying it works well, and that on many platforms) is "sdl" a.k.a.
"sdl". Have ffmpeg create two outputs:
$ ffmpeg -i INPUT -c whatever OUTPUTFILE -c copy -f sdl :0
(You may need to drop the copy codec if sdl cannot handle your input or
it isn't raw, and/or at least adjust the pixel format to one which sdl
handles - but it will report that in an error message, I believe.)
Thanks Moritz, I didn't know about this... but, I can't seem to get it to
work. I believe the codec and/or pixel format (as you suspected) may be
to blame.
Any suggestions for a codec and/or pixel format that:
1) is compatible with the camera mjpeg input (yuvj422p ?)
2) does NOT change the framerate from 30 fps to 10 fps
If I try this:
$ ffmpeg -f v4l2 -input_format mjpeg -framerate 30 -video_size 1280x720 -i
/dev/video2 -map 0:0 -c:v copy -f sdl :0
I get:
[sdl,sdl2 @ 0x3ef9980] Only supports one rawvideo stream
So I try this:
$ ffmpeg -f v4l2 -input_format mjpeg -framerate 30 -video_size 1280x720 -i
/dev/video2 -map 0:0 -c:v rawvideo -f sdl :0
Then I get this:
[sdl,sdl2 @ 0x3a5f980] Unsupported pixel format 'yuvj422p'.
So then I try this.
NOTE: I'm just guessing with yuv422p... I really have no idea what pixel
format to use:
$ ffmpeg -f v4l2 -input_format mjpeg -framerate 30 -video_size 1280x720 -i
/dev/video2 -map 0:0 -c:v rawvideo -pixel_format yuv422p -f sdl :0
But get the same error:
[sdl,sdl2 @ 0x3a5f980] Unsupported pixel format 'yuvj422p'.
So, I try it as an input option:
$ ffmpeg -f v4l2 -input_format mjpeg -pixel_format yuv422p -framerate 30
-video_size 1280x720 -i /dev/video2 -map 0:0 -c:v rawvideo -f sdl :0
(see complete output below)
This doesn't work, but it seems like it tries to work. I briefly see what
I assume is a window flash on the monitor, then it disappears and I get
this error:
av_interleaved_write_frame(): Operation not permitted
One other problem with this particular command is this notice:
[video4linux2,v4l2 @ 0x3b9ff80] The driver changed the time per frame from
1/30 to 1/10
Which I definitely do NOT want.
If I go back to ffplay and use "-pixel_format yuv422p" as an input option:
$ ffplay -f v4l2 -input_format mjpeg -pixel_format yuv422p -framerate 30
-video_size 1280x720 -i /dev/video2
it does work (ie, I see a video window with camera output), BUT I get the
same notice about the framerate:
[video4linux2,v4l2 @ 0x7efd78000bc0] The driver changed the time per frame
from 1/30 to 1/10
Complete output for command that "tries to work". Happy to provide
complete output for any other commands:
$ ffmpeg -f v4l2 -input_format mjpeg -pixel_format yuv422p -framerate 30
-video_size 1280x720 -i /dev/video2 -map 0:0 -c:v rawvideo -f sdl :0
ffmpeg version N-99076-gb0203fa72b Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9 (GCC)
configuration: --enable-gpl --enable-version3 --enable-nonfree
--enable-static --disable-shared --disable-debug --enable-libass
--enable-libfdk-aac --enable-libfontconfig --enable-libfreetype
--enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis
--enable-libvpx --enable-libx264 --enable-libx265 --enable-openssl
--enable-libbluray --enable-libcdio --enable-libtesseract
libavutil 56. 58.100 / 56. 58.100
libavcodec 58.105.100 / 58.105.100
libavformat 58. 54.100 / 58. 54.100
libavdevice 58. 11.101 / 58. 11.101
libavfilter 7. 87.100 / 7. 87.100
libswscale 5. 8.100 / 5. 8.100
libswresample 3. 8.100 / 3. 8.100
libpostproc 55. 8.100 / 55. 8.100
[video4linux2,v4l2 @ 0x3b9ff80] The driver changed the time per frame from 1/30
to 1/10
Input #0, video4linux2,v4l2, from '/dev/video2':
Duration: N/A, start: 2054789.182838, bitrate: 147456 kb/s
Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 1280x720, 147456
kb/s, 10 fps, 10 tbr, 1000k tbn, 1000k tbc
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> rawvideo (native))
Press [q] to stop, [?] for help
Output #0, sdl,sdl2, to ':0':
Metadata:
encoder : Lavf58.54.100
Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 1280x720,
q=2-31, 147456 kb/s, 10 fps, 10 tbn, 10 tbc
Metadata:
encoder : Lavc58.105.100 rawvideo
av_interleaved_write_frame(): Operation not permitted
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.10 bitrate=N/A speed=0.364x
video:1800kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Conversion failed!
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