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• can't read mp4 in opencv3.2 (ubuntu, python3)

  28 mars 2017, par lhk

  I’ve ran into a problem with my opencv installation, it is unable to open an mp4 video. My system is ubuntu 16.04, 64bit, opencv3.2 used from python 3.5.

  VideoCapture.read returns False and None.

  There are other questions with this problem, but they target different platforms or different opencv versions.

  Apparently, I’m missing the proper codec.
  So I ran make uninstall from my build directory, purged opencv* with apt and built from source again. This time making sure that ffmpeg was installed before the compilation.

  Here are my steps :

  • clone opencv and opencv_contrib
  • cd opencv/
  • mkdir build
  • cd build
  • cmake -D CMAKE_BUILD_TYPE=RELEASE     -D CMAKE_INSTALL_PREFIX=/usr/local     -D INSTALL_PYTHON_EXAMPLES=ON     -D INSTALL_C_EXAMPLES=OFF     -D OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules     -D BUILD_EXAMPLES=ON ..
  • make -j 8
  • sudo make install

  I checked the output of cmake, ffmpeg is there :

  Video I/O:
  
  --     DC1394 1.x:                  NO
  
  --     DC1394 2.x:                  NO
  
  --     FFMPEG:                      YES
  
  --       avcodec:                   YES (ver 56.60.100)
  
  --       avformat:                  YES (ver 56.40.101)
  
  --       avutil:                    YES (ver 54.31.100)
  
  --       swscale:                   YES (ver 3.1.101)
  
  --       avresample:                NO
  
  --     GStreamer:                   NO
  
  --     OpenNI:                      NO
  
  --     OpenNI PrimeSensor Modules:  NO
  
  --     OpenNI2:                     NO
  
  --     PvAPI:                       NO
  
  --     GigEVisionSDK:               NO
  
  --     Aravis SDK:                  NO
  
  --     UniCap:                      NO
  
  --     UniCap ucil:                 NO
  
  --     V4L/V4L2:                    NO/YES
  
  --     XIMEA:                       NO
  
  --     Xine:                        NO
  
  --     gPhoto2:                     NO

  But the problem persists. How can I fix this ?

  UPDATE

  I had to manually remove some .so files from /usr/local.

  Then I installed all avi related codecs I could find.
  https://wiki.ubuntuusers.de/Codecs/
  plus libavcodec-extra and ffmpeg

  Then I recompiled and now it works.

• ffmpeg for archival and convertibility

  27 juillet 2021, par Satya

  I've got a couple hundred gigs of *.dv files. I'd like to convert them to H.264 or something else or even leave them alone. The purpose is archival, with an eye to maximum convertibility especially to DVD. The content is family videos.

  


  Would this be fine ?

  


  ffmpeg -i input.dv \
    -c:v libx264 -preset slower \
    -crf 17 \
    -pix_fmt yuv420p \
    output.mp4


  


  I went with the slower preset because encoding time isn't an issue and I'd like a smaller file size. crf 17 is for least-lossy while being widely playable. I read somewhere that yuv420p is needed for some Quicktime players.

  


  Should I throw in -c:a aac for AAC audio ? The audio is voice only, no need for music-hall quality.

  


  I looked at https://trac.ffmpeg.org/wiki/Encode/H.264 for previous research and that's where I got those settings, but it is silent on the audio settings.

  


  Edited : My priorities, in order of importance, are :

  


  

  1. Compatibility

  


  2. Losslessness (doesn't have to be 100% lossless, hence crf of 17 and not 0)

  


  3. File size

  


  


  Most of the input files say this :

  


  [lavf] stream 0: video (dvvideo), -vid 0
[lavf] stream 1: audio (pcm_s16le), -aid 0
VIDEO:  [dvsd]  720x480  0bpp  29.970 fps  25000.0 kbps (3051.8 kbyte/s)
Selected video codec: [ffdv] vfm: ffmpeg (FFmpeg DV)
AUDIO: 32000 Hz, 2 ch, s16le, 1024.0 kbit/100.00% (ratio: 128000->128000)
Selected audio codec: [pcm] afm: pcm (Uncompressed PCM)


  


  Output from ffmpeg :

  


  Stream #0:1: Audio: pcm_s16le, 32000 Hz, stereo, s16, 1024 kb/s


  


• send point to point video stream using ffmpeg with rtsp (c++)

  8 décembre 2015, par seleciii44

  I need to send a h264 encoded video stream to a(only one) specific IP address with RTSP protocol on a windows PC with C++. I’m trying to use the FFMPEG library.

  I used the example in this post and i can play the stream as :

  ffplay -rtsp_flags listen -i rtsp://127.0.0.1:8554/live.sdp

  The problem is, according to the solution of post i need a server. Where -rtsp_flags listen option of ffplay behaves like a server.

  On the other hand, according to StreamingGuide of ffmpeg i can send a point to point stream like :

  ffmpeg -i INPUT -acodec libmp3lame -ar 11025 --f rtp rtp://host:port

  This is fine and works well. But i need to use rtsp. According to StreamingGuide again,

  Another option is to use RTP (which by default uses UDP) but by
  specifying it use TCP :

  ffmpeg -i input -f rtsp -rtsp_transport tcp rtsp://localhost:8888/live.sdp

  which seems to be what i’m looking for. Yet the ffmpeg tool seems to be doing nothing when i try this method (don’t know why i need tcp,but udp does not work neither). Why is that ?

  FFMPEG protocols documentation, says that i need to use a media server to send the video.

  • Why would i need a media server to just send the video stream to another PC or whatever ?
  • If i need a media server, how does the IP Camera sends the stream ?
  • If i have no option but to use a media server, could some one please recommend a server for Windows 7 ?
    • ffserver is only for linux
    • live555mediaServer seems to be used for local files or am i wrong ?
    • ..?

  Best regards,
  Gokhan.