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• ffmpeg : how to resample audio file

  9 juin 2021, par xrfang

  I need to convert a 44KHz stero m4a audio file to 22KHz mono mp3 VBR file, how can I do that with ffmpeg on linux terminal ? Thanks.

  


• How can I use avformat_open_input function (ffmpeg)

  5 mai 2016, par johncarrie

  I have bought a HD HDMI to UVC device which has HDMI video source input and UVC for video output here.
  I connect it from laptop A (input source HDMI) to laptop B (output USB).
  I have installed Ubuntu 14.04 desktop on Laptop B and Win 8.1 on Laptop A.
  B also have ffmpeg, opencv and sdl library installed.
  My target is to capture video and audio from A via HD HDMI to UVC on B.
  So I have decided to use libav of ffmpeg.
  I saw this and used avformat_open_input function but this function returned error.
  I thought that the error was occurred because the second parameter of avformat_open_input (const char * url) was invalid.
  I know that the url should be like video:video device name:audio:audio card name.
  How can I indicate the device names ?

  Here’s the result of v4l2-ctl --list-devices command in terminal.

  HD WebCam (usb-0000:02:03.0-1):   
  
      /dev/video0
  
  HD TV CAM (usb-0000:03:00.0-2.1):   
  
      /dev/video1

  And the result of arecord -l in terminal.

  **** List of CAPTURE Hardware Devices ****  
  
  card 0: AudioPCI [Ensoniq AudioPCI], device 0: ES1371/1 [ES1371 DAC2/ADC]  
  
  Subdevices: 1/1  
  
  Subdevice #0: subdevice #0    
  
  card 1: CAM [HD TV CAM], device 0: USB Audio [USB Audio]    
  
  Subdevices: 1/1  
  
  Subdevice #0: subdevice #0  

  Thank you.

• Python/FFMPEG command line issues

  1er mars 2019, par 12hys

  I have a problem with running an FFMPEG command from within a Python script. When I run the following command from the terminal, I can stream video and audio from my attached webcam (Logitech C310) and output to file "out.avi" without any errors.

  ffmpeg -f alsa -i default -itsoffset 00:00:00 -f video4linux2 -s 1280x720 -r 25 -i /dev/video0 out.avi

  When I run the same command in a Python script below,

  def call_command(command):
  
      subprocess.Popen(command.split(' '))
  
  
  
  call_command("ffmpeg -f alsa -i default -itsoffset 00:00:00 -f video4linux2 -s 1280x720 -r 25 -i /dev/video0 out.avi")

  it gives me the error :

  Input #0, alsa, from 'default':
  
    Duration: N/A, start: 1317762562.695397, bitrate: N/A
  
    Stream #0.0: Audio: pcm_s16le, 44100 Hz, 1 channels, s16, 705 kb/s
  
  [video4linux2 @ 0x165eb10]Cannot find a proper format for codec_id 0, pix_fmt -1.
  
  /dev/video0: Input/output error

  Could anyone shed some light on what could be going on here ? I’ve tried using os.system() as well as subprocess.call() and it gives me the same errors. I’m not sure where to start on what could be going wrong here. I tried searching for the "video4linux2 Cannot find a proper format for codec_id 0, pix_fmt -1" error, but couldn’t find anything consistent.

  I’ve also tried putting the "ffmpeg -f..." command in a shell script "test.sh", and giving it executable permissions. I then open terminal, and run "./test.sh", and it works. When I try calling the command "./test.sh" from within my Python script, I’m left with the original error as before. This is the Python command I tried with the test.sh script :

  subprocess.call(["./test.sh"])