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• How do I use ffmpeg's `filter_complex` `volume` filter on videos that might not have an audio track ?

  9 mars 2023, par jaygooby

  I'm mixing new audio tracks into videos, and I want the original video audio to be at a lower volume in the mix :

  


  ffmpeg -i audio.wav -i video.mp4 -c:v copy -filter_complex "[1:a:0]volume=0.5[originalAudio]; [0:a:0][originalAudio]amix=inputs=2[m]" -map [m] -map 1:v:0 tmp.mp4


  


  that sets the original video audio to be 50% less than it was, when audio.wav is mixed with it. This works fine until there's a video with no audio track. Then I get the error :

  


  Stream specifier ':a:0' in filtergraph description [1:a:0]volume=0.05[originalAudio]; [0:a:0][originalAudio]amix=inputs=2[m] matches no streams.


  


  because the video has no audio track.

  


  Is there a way for me to use ffmpeg filters in the same call, to ensure there's an audio track if one is originally missing, so I don't need to check for the presence of an audio track using an additional step with ffprobe, mediainfo etc ?

  


  [Edit 1] Looks like I need to add a anullsrc track to the video inside the filter_complex, and then not specifically choose which audio track from the video I want, so either the original or the new silent one (if it's the only one present) is selected via ffmpeg's automatic stream selection...

  


  [Edit 2] Something like this, where I have 2 audio inputs, the first is silence and the second is the input wav. Use concat to pick either the silence or the video audio, use the result of that to reduce the volume, then mix in the new audio to the result of that, but I'm not there yet :

  


  ffmpeg -f lavfi -i anullsrc \
       -i audio.wav \
       -i video.mp4 \
       -c:v copy \
       -filter_complex \
       "[0:a] [2:a] concat=n=2:v=0:a=1 [silence-or-video-audio];
        [silence-or-video-audio]volume=0.5[reduced-audio]; [1:a:0][reduced-audio]amix=inputs=2[mixed-audio]" \
       -map "[mixed-audio]" \
       -map "[2:v:0]" \
       tmp.mp4


  


  The error is : Stream specifier ':a' in filtergraph description [0:a] [2:a] concat=n=2:v=0:a=1 [silence-or-video-audio]; [silence-or-video-audio]volume=0.5[reduced-audio]; [1:a:0][reduced-audio]amix=inputs=2[mixed-audio] matches no streams.

  


• ffmpeg php makes system unresponsive

  6 mars 2016, par Akshay Khetrapal

  I am trying to create a video on my web application using images as input by the user.
  I am using ffmpeg currently to encode the output. However, my system becomes unresponsive each time I execute the command.

  I am using exec command of php and following is my ffmpeg command.

  ffmpeg -i bg2.png -i overlay1.png -filter_complex "[1:v]scale=0:0[fg]; [0:v][fg]overlay=y=-'t*w*0.1':shortest=1[v]"  -map "[v]" -t 10 out.mkv

  I’d appreciate if you could also share some good resources to learn more about ffmpeg on web and other alternatives.

• Creating a VOD ABR system with HLS

  19 juillet 2016, par Matteo

  I know this is a specific question but I’m new to this and have spent weeks trying to solve this problem.

  I’m creating a mobile app and need to have Video on Demand (VOD) live streaming. Right now I’m converting MP4 video files into HLS using FFMPEG and broadcasting from a server but the load time is pretty long for 3G connections (low bandwith).

  Has anyone else set up this type of system that can help ?

  It looks like I need Adaptive Bitrate Streaming (ABR) and a media server with a CDN.

  My question is - #1 - Can I get away with not using a CDN ? Or perhaps not using a "media server" but just a regular server

  2 - Is it practical to use FFPMEG to set up an ABR stream with HLS

  I know I probably wont get a response to this question but I thought it was worth a shot.

  Thanks