python - Pipe raw OpenCV images to FFmpeg -

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here's straightforward example of reading off web cam using opencv's python bindings:

'''capture.py''' import cv, sys cap = cv.capturefromcam(0)                    # 0 /dev/video0 while true :     if not cv.grabframe(cap) : break     frame = cv.retrieveframe(cap)     sys.stdout.write( frame.tostring() )

now want pipe output ffmpeg in:

$ python capture.py | ffmpeg -f image2pipe -pix_fmt bgr8 -i - -s 640x480 foo.avi

sadly, can't ffmpeg magic incantation quite right , fails with

   libavutil     50.15. 1 / 50.15. 1   libavcodec    52.72. 2 / 52.72. 2   libavformat   52.64. 2 / 52.64. 2   libavdevice   52. 2. 0 / 52. 2. 0   libavfilter    1.19. 0 /  1.19. 0   libswscale     0.11. 0 /  0.11. 0   libpostproc   51. 2. 0 / 51. 2. 0 output #0, avi, 'out.avi':     stream #0.0: video: flv, yuv420p, 640x480, q=2-31, 19660 kb/s, 90k tbn, 30 tbc [image2pipe @ 0x1508640]max_analyze_duration reached [image2pipe @ 0x1508640]estimating duration bitrate, may inaccurate input #0, image2pipe, 'pipe:':   duration: n/a, bitrate: n/a     stream #0.0: video: 0x0000, bgr8, 25 fps, 25 tbr, 25 tbn, 25 tbc swscaler: 0x0 -> 640x480 invalid scaling dimension
  • the captured frames 640x480.
  • i'm pretty sure pixel order opencv image type (iplimage) gbr, 1 byte per channel. @ least, that's seems coming off camera.

i'm no ffmpeg guru. has done successfully?

took bunch of fiddling figured out using ffmpeg rawvideo demuxer:

python capture.py | ffmpeg -f rawvideo -pixel_format bgr24 -video_size 640x480 -framerate 30 -i - foo.avi

since there no header in raw video specifying assumed video parameters, user must specify them in order able decode data correctly:

  • -framerate set input video frame rate. default value 25.
  • -pixel_format set input video pixel format. default value yuv420p.
  • -video_size set input video size. there no default, value must specified explicitly.

and here's little power users. same thing using vlc stream live output web, flash format:

python capture.py | cvlc --demux=rawvideo --rawvid-fps=30 --rawvid-width=320 --rawvid-height=240  --rawvid-chroma=rv24 - --sout "#transcode{vcodec=h264,vb=200,fps=30,width=320,height=240}:std{access=http{mime=video/x-flv},mux=ffmpeg{mux=flv},dst=:8081/stream.flv}"

edit: create webm stream using ffmpeg , ffserver

python capture.py | ffmpeg -f rawvideo -pixel_format rgb24 -video_size 640x480 -framerate 25 -i - http://localhost:8090/feed1.ffm

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