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• avconv "select" filter doesn't discard first frames

  1er avril 2014, par user2152106

  I'm trying to segment a video using avconv's "select" filter to extract only a specific range of frames from the input file. As an example, imagine I have a 60fps video file called input.mp4, with 3000 frames (i.e. 50 seconds), and I run

  avconv -i input.mp4 -vf "select='lt(n,2000)'" output1.mp4
  
  avconv -i input.mp4 -vf "select='gte(n,2000)'" output2.mp4

  What I expect is that output1.mp4 has the first 2000 frames of input.mp4 (and lasts 33 seconds), and output2.mp4 has the last 1000 (and lasts 17 seconds).

  I count the frames by running

  avconv -i video.mp4 -vcodec copy -an -f null /dev/null 2>&1 | grep 'frame='

  and checking the value assigned to 'frame'.

  What I actually get, is that output1.mp4 has 2000 frames and lasts 33 seconds, but output2.mp4 has 2999 frames, and still lasts the full 50 seconds. When I open output2.mp4, I notice that the first 2000 frames of the video are actually just a repetition of the 2000th frame of the input, i.e. the first 2000 frames seem to be correctly filtered, but replaced by the first of the accepted frames.

  This is not a pts problem. I check the number of packets and their relative pts using avprobe :

  avprobe -show_packets output2.mp4
  
  echo $(avprobe -show_packets output2.mp4 2>/dev/null | grep PACKET | wc -l)/2 | bc

  I see that there are actually 2999 packets.

  What am I doing wrong ?

  Side questions :

  • Assuming I'm doing something wrong, why does output2.mp4 contain 2999 rather than the full 3000 ?
  • The behaviour doesn't change whether I use the "gte" or "gt" function in the filter. Why could that be ?

• ffserver Error writing frame to output

  28 mars 2014, par GarciaPL

  I am new to ffmpeg and ffserver. I spent a lot of time to stream the .avi file using ffserver. Below is my config.

  Port 8090                      # Port to bind the server to
  
  BindAddress 0.0.0.0
  
  MaxHTTPConnections 2000
  
  MaxClients 1000
  
  MaxBandwidth 10000             # Maximum bandwidth per client
  
                                 # set this high enough to exceed stream bitrate
  
  CustomLog -
  
  NoDaemon                       # Remove this if you want FFserver to daemonize after start
  
  
  
  RTSPPort 7654
  
  RTSPBindAddress 0.0.0.0
  
  
  
  <feed>               # This is the input feed where FFmpeg will send
  
     File ./feed1.ffm            # video stream.
  
     FileMaxSize 1G              # Maximum file size for buffering video
  
     ACL allow 127.0.0.1
  
     ACL allow 192.168.0.0 192.168.0.255
  
  </feed>
  
  
  
  <stream>
  
      Format avi
  
      Feed feed1.ffm
  
  
  
      VideoCodec libvpx
  
      VideoFrameRate 30
  
      VideoBitRate 800
  
      VideoSize 720x576
  
  
  
      AudioCodec aac
  
      Strict -2
  
      AudioBitRate 128
  
      AudioChannels 2
  
      AudioSampleRate 44100
  
      AVOptionAudio flags +global_header
  
  </stream>
  
  
  
  <stream>            # Server status URL
  
     Format status
  
     ACL allow localhost          
  
     ACL allow 192.168.0.0 192.168.255.255
  
  </stream>
  
  
  
  <redirect>    # Just an URL redirect for index, Redirect index.html to the appropriate site
  
     URL http://www.ffmpeg.org/
  
  </redirect>

  So, to start my ffserver I use this command :

  ffserver -d -f ffserver.conf

  and after that I start stream of this avi file using ffmpeg :

  ffmpeg -re -i russian.avi -c:v libx264 -loop 1 http://192.168.1.165:8090/feed1.ffm

  unfortunately I received two errors repeated many of times :

  Too large number of skipped frames 60120709615 > 60000
  
  Error writing frame to output

  I searched the entire internet....but I found nothing what would be valuable.

• How to generate stereo sine wave using FFMPEG ?

  1er janvier 2020, par John Doe

  I’m trying to generate a stereo sine wave using FFMPEG (batch file), but have a different frequency for left and right. So far I have this :

  ffmpeg -f lavfi -i "sine=frequency=1000:duration=60" -ac 2 "binaural.wav"

  But it creates the same frequency for both left and right.
  Is this possible ?