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• How does Rust work with process arguments ?

  1er octobre 2022, par SoptikHa

  I'm really confused about Rust processes. I'm trying to call something like this :

  



  ffmpeg -i path/to/test-video.webm -ab 160k -ac 2 -vn -f mp3 -


  



  This should extract sound out of video and send it to stdout. So I've done this :

  



  let sound: std::process::Output = Command::new("ffmpeg")
    .arg(format!("-i {}", args.input.to_str().unwrap()))
    .arg("-ab 160k")
    .arg("-ac 2")
    .arg("-vn")
    .arg("-f mp3")
    .arg("-")
    .stdout(Stdio::piped())
    .stdin(Stdio::inherit())
    .stderr(Stdio::inherit())
    .output()
    .unwrap();


  



  But for some reason, this doesn't work. It prints this to stderr :

  



  Unrecognized option 'i path/to/test-video.webm'.
Error splitting the argument list: Option not found


  



  When I remove the slashes from args (so it looks like .arg(format!("i {}", ...)).arg("ab 160k")..., I get this :

  



  Output file #0 does not contain any stream


  



  I think I misunderstood how this works, but I tested it on other applications and it seemed to work the way I'm doing it now. What did I miss, how does Rust work with these arguments ?

  



  And just to be clear, I know about the ffmpeg crates, but they don't work for me for some reason, I can't even compile them.

  


• libavdevice.so.57 : failed to map segment from shared object : Permission denied"

  10 septembre 2016, par user3579130

  I have successfully installed ffmpeg ver. 4.4.7 on centos, with shared enabled as such :

  [root@localhost ~]# ffmpeg
  
  ffmpeg version N-81555-g496d97f Copyright (c) 2000-2016 the FFmpeg developers
  
    built with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-17)
  
    configuration: --prefix=/usr/local/ffmpeg_build --extra-cflags=-I/usr/local/ffmpeg_build/include --extra-ldflags=-L/usr/local/ffmpeg_build/lib --bindir=/usr/local/bin --pkg-config-flags=--static --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libx264 --enable-libx265 --enable-shared
  
    libavutil      55. 29.100 / 55. 29.100
  
    libavcodec     57. 54.102 / 57. 54.102
  
    libavformat    57. 48.102 / 57. 48.102
  
    libavdevice    57.  0.102 / 57.  0.102
  
    libavfilter     6. 60.100 /  6. 60.100
  
    libswscale      4.  1.100 /  4.  1.100
  
    libswresample   2.  1.100 /  2.  1.100
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Hyper fast Audio and Video encoder
  
  usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...

  However, when I run in php, through exec I get

  "/usr/local/bin/ffmpeg : error while loading shared libraries :
  libavdevice.so.57 : failed to map segment from shared object :
  Permission denied"

  I know the web server executes the command as user ’apache’ and not root, but I installed ffmpeg in /usr/local/ffmpeg_build for that specific reason, so that the regular users can use ffmpeg.

  What did I miss ? What does this error mean ?

• FFmpeg av_read_frame returns packets from audio stream

  1er août 2018, par yultan

  I am currently trying to learn the FFmpeg API, following this tutorial. However, I already have issues with the first lesson on video decoding. My code is basically the same as the one from the tutorial except I am using C++. My issue is that the video stream does not match the one from the packet returned by av_read_frame.

  The video stream is obtained looping on the available streams until the video stream is found.

  for(int i = 0; i < pFormatCtx->nb_streams; i++) { // nb_streams == 2
  
  
  
      if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
  
          videoStream = i; 
  
          break; // videoStream == 0
  
      }
  
  }

  Then when retrieving the frame data, it seams grabbing the audio channel.

  while(av_read_frame(pFormatCtx, &packet) >= 0) { // read returns 0
  
  
  
      // Is this a packet from the video stream?
  
      if(packet.stream_index == videoStream) { 
  
          //packet.stream_index == 1, which correspond to the audio stream
  
      } 
  
  }

  I have not found examples online where this test is actually failing. Have I miss some way to specify the stream_index that is not in the tutorial ? Maybe the tutorial is not up to date and is doing something wrong ? If so, what is the correct way to extract the frame data ? In case that matters, I am using the latest FFmpeg 4.0.2 build, on Windows 64-bits, compiling with Visual Studio 2017.

  On videos with no sound, the two streams match and I am able to decode and display the frames correctly.