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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.

  


• How can I use ffmpeg or vlc to sample audio frequency and volume(DB value)

  26 février 2014, par poc

  I want to capture the audio's frequency and volume from RTSP streaming.

  I want to sample it every second, But can not find how to get it via vlc or ffmpeg

  When executing the following line, it only shows the video bit rate information and nothing about audio.

  ffmpeg -i rtsp://172.19.1.40/live.sdp -acodec copy -vcodec copy lala.avi

• RTSP player volume control using FFMPEG iOS7

  21 mai 2014, par sansid1983

  I am able to show 2 RTSP video streams from 2 IP cameras by working on https://github.com/durfu/DFURTSPPlayer.

  The video plays smoothly and audio is also working fine. But i am unable to increase or decrease volume of each RTSPPlayer. FFMPEG framework is included in it. If any has an idea how i can enable this feature please do share.