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• Select Input device in FFMPEG direct show

  1er mars 2014, par M.Yazdian

  I want to select my camera for input video through dshow in FFMPEG.
  I can do it, But I like to do that by use webcam ID not webcam name...!!!

  ffmpeg -f dshow -i video-"A4tech USB Camera" -f flv rtmp://192.168.1.2/live/Camera1

  In the dshow I should set the name of webcam in the video argument, So I need to set the device number to select webcam.

  For example Webcam number 4 instead video="A4tech USB Camera".

  Please advise to do that

  Thanks in advance.

• Use ffmpeg to show a webcam live stream in a browser

  20 juillet 2020, par Toast

  I have a webcam that is connected to a server and I'd like to view a live stream of it in a web browser.

  


  I'd like to include a video tag like this :

  


  <video></video>&#xA;

  


  What is an ffmpeg command that will send a video stream to browser clients ?
I managed to record a video to disk with this command :

  


  ffmpeg -f v4l2 -i /dev/video0 output.mkv


  


  I'm not sure if rtsp and ffmpeg are a good choice and I'm open for alternative suggestions.
I'm looking for a solution that is simple to setup and demo. Scalability and support for older browsers don't matter and audio isn't needed. I'd prefer a solution that sends compressed video instead of individual images (MJPG).

  


• Can't fix timestamp of WebM video with dynamic resolution using FFmpeg

  11 février 2019, par Yurii Kit

  I’m developing the platform for 1-1 video calls with recording. For my purposes, I work with the following stack : WebRTC, Kurento Media Server, FFmpeg.

  1. It works perfectly in an ideal environment, but if my users have a poor connection, after the recording I see a lot of problems with the out of sync audio and video tracks.

     As I understand, the problem appears due to the incorrect timestamp, so I’m doing a bit post-processing where I generate a new timestamp and it helps !

     Here is the command example :

     ffmpeg -fflags +genpts -acodec libopus -vcodec libvpx \
     
         -i in.webm \
     
         -filter_complex "fps=30, setpts=PTS-STARTPTS" \
     
         -acodec libvorbis -vcodec libvpx \
     
         -vsync 1 -async 1 -r 30 -threads 4 out.webm

  2. After that, I’ve faced one more problem. If the user has a poor connection, WebRTC can dynamically change the video resolution. After the post-processing for such type of videos (with the different resolutions during the video) I see the frozen image until the end of the video and it started from the moment, where the resolution was dynamically changed. There are no error in the FFmpeg logs, just information about changing the resolution :

     [libvpx @ 0x559335713440] dimension change! 480x270 -> 320x180
     
     -async is forwarded to lavfi similarly to -af aresample=async=1:min_hard_comp=0.100000.

     After analyzing the logs, I realized that the problem was due to the STARTPTS parameter, which, after automatically changing the extension, became very large (equal to the number of frames that were before it). I tried to remove STARTPTS and leave only PTS.

     After that, the video started to work well, but only until the video resolution are dynamically changed, then again the audio and video tracks are out of sync.

     I’ve tried to scale videos to a static resolution before fixing timestamp and it helps. But it’s a little bit extra work. Command example :

     ffmpeg -acodec libopus -vcodec libvpx \
     
         -i in.webm \
     
         -vf scale=640:480 \
     
         -acodec libvorbis -vcodec libvpx \
     
         -threads 4 out.webm

     Also I’ve tried to combine both commands using filter_complex, but it didn’t work.

     I’ve worked with FFmpeg not so many time so far, so, maybe I’m doing something wrong ? Maybe there are some easier ways to do that ?

     Since Kurento uses GStreamer for the video recording, so maybe it would be a better option to reconfigure Kurento to fix timestamp during the video recording ?

  I can provide any videos and commands which I use.

  I’m using :
  Kurento Media Server 6.9.0,
  FFmpeg 4.1