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• How can I convince ffserver to save a locally-sourced webcam stream to a file in high resolution AND stream it in lower resolution ?

  2 novembre 2015, par Dominic Jacobssen

  We have a remote Linux machine, accessible over VPN, which has a USB webcam. We want to use this for video conferencing, but we also want to store the stream for archiving.

  Since the streaming bandwidth is limited, it makes sense to capture the stream on the same machine as the webcam and rsync that across after-the-fact, rather than trying to capture the streamed content, which is necessarily going to be poor quality.

  We’re trying to use ffmpeg and ffserver to achieve this, but with little success. Most of the articles on the internet either deal with just streaming a webcam, or rebroadcasting a remote stream. We found we had to recompile ffserver because of a missing "my_addr->sin_family = AF_INET ;" in the version of ffserver.c we had been using, since fixed in git.

  Here’s the ffserver.conf we’re trying to use :

  Port 43688
  
  BindAddress 127.0.0.1
  
  MaxHTTPConnections 2000
  
  MaxClients 1000
  
  MaxBandwidth 1000
  
  CustomLog -
  
  NoDaemon
  
  <feed>
  
  ReadOnlyFile /tmp/feed.ffm
  
  FileMaxSize 20M
  
  ACL allow 127.0.0.1
  
  </feed>
  
  <stream>
  
  Feed feed.ffm
  
  Format mp4
  
  VideoSize qvga
  
  VideoGopSize 12
  
  VideoHighQuality
  
  Video4MotionVector
  
  VideoCodec libx264
  
  VideoBitRate 100
  
  VideoBufferSize 40
  
  VideoFrameRate 5
  
  VideoQMin 3
  
  VideoQMax 31
  
  AudioCodec libfaac
  
  AudioBitRate 32
  
  AudioChannels 2
  
  AudioSampleRate 22050
  
  ACL allow localhost
  
  </stream>

  When we fire this up, we get the error :

  Unable to create feed file '/tmp/feed.ffm' as it is marked readonly

  Fair enough, but this is not what is implied in the docs. Changing the directive to :

  File /tmp/feed.ffm

  allows ffserver to fire up and appear to sit and wait for ffmpeg to connect to it. However, when we fire up ffmpeg with the command :

  ffmpeg -f alsa -i pulse -r 16000 -f video4linux2 -s qvga -i /dev/video0 -r 5 -f mp4 -vcodec libx264 -sameq -acodec libfaac -ab 32k http://127.0.0.1:43688/feed.ffm

  then the webcam lights up and ffserver acknowledges the connection with the messages :

  New connection: POST /feed.ffm
  
  [POST] "/feed.ffm HTTP/1.1" 200 0

  but after a few seconds we get the errors :

  [mp4 @ 0x264b160] muxer does not support non seekable output
  
  Could not write header for output file #0 (incorrect codec parameters ?)

  We’ve tried various other formats (mpeg, mpegts, avi) and codecs (mpeg1video, mpeg2video, mpeg4), all without success.

  Moreover, we were under the impression that ffserver could reencode input format to a lower resolution for streaming, but if the stream resolution doesn’t match the feed resolution, we get an error about the resolutions not matching.

  Has anyone ever managed to get this working correctly ? I’ve read about vlc being able to do something like this, but the vlc command lines are well nigh impenetrable.

  Thanks !

  Dominic

• nutenc : choose for non audio streams a timebase with finer resolution.

  1er octobre 2012, par Michael Niedermayer

  nutenc : choose for non audio streams a timebase with finer resolution.

• using FFMPEG commands , can i get the default values of any media file, like resolution, audio codec, video codec..etc

  30 novembre 2012, par rohit k.

  like for eg.
  if i enter the output extension '.avi' , i should get the default audio codec used , default video codec used , etc... Is there a command for this ?