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I want to record the best possible video file (in terms of resolution/framerate/colors) from my webcam.
Right now I am using this command:

ffmpeg -f v4l2 -framerate 25 -video_size 640x480 -i /dev/video0 output.mkv

My webcam seems to support this:

$ ffmpeg -f v4l2 -list_formats all -i /dev/video0
…
[video4linux2,v4l2 @ 0xf07d80] Raw       : yuyv422 : YUV 4:2:2 (YUYV) : 640x480 160x120 176x144 320x176 320x240 352x288 432x240 544x288 640x360
[video4linux2,v4l2 @ 0xf07d80] Compressed:   mjpeg :            MJPEG : 640x480 160x120 176x144 320x176 320x240 352x288 432x240 544x288 640x360

I guess I got the resolution part, but how can I improve my command line to:

  • Use no compression (I suspect the current .mkv output is compressed)
  • Use the best framerate that the camera&computer is capable of, without duplicating frames either (no point saving the file at 100 fps if the webcam is not capable of capturing frames at that rate)
  • All ideas to further improve the video quality are welcome
Ray
  • 181

2 Answers2

1

I am used: ffmpeg -f video4linux2 -input_format yuyv422 -video_size 640x480 -i /dev/video0 -c:v copy 640x480.mkv

Pisin Vasya
  • 11
  • 1
1

Do you really want no compression? Uncompressed video would be very large. Or do you want no transcoding? Or lossless?

No compression can be achieved as mentioned at https://superuser.com/a/1302502/128124

First determine your available formats with:

v4l2-ctl --list-formats-ext

as mentioned at: How can I list the available video modes for a USB webcam in Linux?

The highest ones for me are:

        [0]: 'YUYV' (YUYV 4:2:2)
                Size: Discrete 1280x720
                        Interval: Discrete 0.100s (10.000 fps)
        [1]: 'MJPG' (Motion-JPEG, compressed)
                Size: Discrete 1280x720
                        Interval: Discrete 0.033s (30.000 fps)
                        Interval: Discrete 0.067s (15.000 fps)

You can then also check:

ffmpeg -f v4l2 -list_formats all -i /dev/video0

which contains for my device:

video4linux2,v4l2 @ 0x5579b13df240] Raw       :     yuyv422 :           YUYV 4:2:2 : 640x480 320x180 320x240 352x288 424x240 640x360 848x480 960x540 1280x720
[video4linux2,v4l2 @ 0x5579b13df240] Compressed:       mjpeg :          Motion-JPEG : 640x480 320x180 320x240 352x288 424x240 640x360 848x480 960x540 1280x720

Then, If I record two 3.5 second very similar video of my making faces on the setup described at https://askubuntu.com/questions/348838/how-to-check-available-webcams-from-the-command-line/848390#848390 rev 18 with:

ffmpeg -y -f v4l2 -framerate 30 -video_size 1280x720 -input_format mjpeg -i /dev/video0 -c copy out.mjpeg.mkv
ffmpeg -y -f v4l2 -framerate 30 -video_size 1280x720 -input_format yuyv422 -i /dev/video0 -c copy out.yuyv422.mkv

the sizes are about:

  • 15MB
  • 60MB

and ffprobe confirms respectively:

    Stream #0:0: Video: mjpeg (Baseline), yuvj422p(pc, bt470bg/unknown/unknown), 1280x720, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
    Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 1280x720, 10 fps, 10 tbr, 1k tbn, 1k tbc (default)

Lossless is discussed at:

Tested on Ubuntu 20.04, Lenovo ThinkPad P51.

Ciro Santilli OurBigBook.com
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