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• Convert PCM to AAC using PyAV

  26 août 2022, par Dave Johansen

  I need to convert PCM (G.711U) audio to AAC in realtime. I've been able to do it with ffmpeg, but would like to use PyAV to have direct control and not have to run a separate process. What's the best way to do that ?

  


  cat input.raw | ffmpeg -hide_banner -f mulaw -ar 8000 -ac 1 -i - -c:a aac -f adts - > output.mp4


  


  (NOTE : in the actually use case there aren't actual files for input.raw and output.mp4 and those are just streaming data but I did them to be able to show the example)

  


• error occured on -pix_fmt in ffmpeg while converting from .mov to mp4 file

  7 avril 2016, par Amey

  I am trying to convert .mov to .mp4 using ffmpeg my command is :

  ffmpeg -i input.mov -vcodec libx264 -acodec copy output.mp4

  but its giving me error like this

      [buffer @ 00000000059bf480] Unable to parse option value "-1" as pixel format
  
  Last message repeated 1 times

  [buffer @ 00000000059bf480] Error setting option pix_fmt to value -1.
  [graph 0 input from stream 0:4 @ 00000000043fd8a0] Error applying options to the
  filter.
  Error opening filters !

  even I tried for another command

  ffmpeg -i input.mov -vcodec copy -acodec copy output.mp4

  but it converts only some part and first part is blank with sound then after some time picture is coming..

  I have two Q’s

  1] for first command what is -pix_fmt and what value to be set for ?

  2] for second command why it was giving only some part, as I am copying everything vcodec as well acodec..

  please guide me ..!!

• FFmpeg low framerate when adding audio

  22 juillet 2021, par Massi

  we are sending a video from a Linux PC with GPU (Alienware M15 R2 so very strong in hardware) connected to a Logitech Brio 4K resolution camera.
We are using ffmpeg and in particular the following command :

  


  ffmpeg -re -hwaccel cuvid -hwaccel_output_format cuda -f v4l2 -input_format mjpeg -framerate 30 -video_size 3840x2160 -i /dev/video4 -f pulse -i default -c:v h264_nvenc -tune ull -preset llhq -zerolatency true -pix_fmt rgb0 -c:a aac -aac_coder fast -ar 44100 -b:a 256k -b:v 25000k -threads 0 -f flv "rtmp ://192.168.1.1/WebRTCAppEE/XXX"

  


  As you can see this is the part related to audio "-c:a aac -aac_coder fast -ar 44100 -b:a 256k"
If we send the script WITHOUT the audio part, we see it very fluid even in 4K resolution, with 30 FPS, but of course with no audio.
If we send the script WITH the audio part, the FPS goes down to 19-20 and the video is no more fluid. In this case we tried also to downgrade the video quality, but the result is always the same, the video is not fluid, even if the PC has not the CPU and GPU very loaded.
Would you suggest another script or some correction in order to avoid this problem and stream a video getting both video and audio from a device ?