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• Crop MP3 to first 30 seconds

  2 décembre 2016, par Cheekysoft

  Original Question

  I want to be able to generate a new (fully valid) MP3 file from an existing MP3 file to be used as a preview — try-before-you-buy style. The new file should only contain the first n seconds of the track.

  Now, I know I could just "chop the stream" at n seconds (calculating from the bitrate and header size) when delivering the file, but this is a bit dirty and a real PITA on a VBR track. I’d like to be able to generate a proper MP3 file.

  Anyone any ideas ?

  Answers

  Both mp3split and ffmpeg are both good solutions. I chose ffmpeg as it is commonly installed on linux servers and is also easily available for windows. Here’s some more good command line parameters for generating previews with ffmpeg

  • -t <seconds></seconds> chop after specified number of seconds
  • -y force file overwrite
  • -ab <bitrate></bitrate> set bitrate e.g. -ab 96k
  • -ar <rate hz="hz"></rate> set sampling rate e.g. -ar 22050 for 22.05kHz
  • -map_meta_data <outfile>:<infile></infile></outfile> copy track metadata from infile to outfile

  instead of setting -ab and -ar, you can copy the original track settings, as Tim Farley suggests, with :

  • -acodec copy

• Interact with ffmpeg from a .NET program - Write Input

  7 mai 2015, par Shimmy

  In reference to this question, as you can see I managed to run and receive data from the program.

  However I didn’t manage to submit data to it, for instance, while converting a file, pressing q immediately stop conversion and stops the program.
  I need my application to support stopping the process as well, and I think this should be done by passing this parameter to the ffmpeg app, since I want it to take care of all uncollected resource or whatever dust it would leave behind if I would just go and use process.Kill()

  Here is what I’ve tried :

  static int lineCount = 0;
  
  static bool flag;
  
  static void process_ErrorDataReceived(object sender, DataReceivedEventArgs e)
  
  {
  
    Console.WriteLine("Error ({1:m:s:fff}: {0})", lineCount++,
  
        DateTime.Now);
  
  
  
    if (e.Data != null && string.Equals(e.Data,"Press [q] to stop, [?] for help")) 
  
      flag = true;
  
  
  
    if (flag)
  
    {
  
      flag = false;
  
      Console.WriteLine("Stopping ({0:m:s:fff})...", DateTime.Now);
  
      process.CancelErrorRead();
  
      process.CancelOutputRead();
  
      process.StandardInput.WriteLine("q");
  
    }   
  
  
  
    Console.WriteLine(e.Data);
  
    Console.WriteLine();
  
  }

  But it doesn’t do anything, seems that once the conversion has been requested, I have no control on it any more, I can only receive output from it. Running it as stand alone does allow me interaction of course.

  What am I missing here, is it a different trick in submitting the output or the code in previous answer is wrong, or I should have chosen a different approach ?

  For your attention, RedirectStandardInput is on.

  NOTE : as you can see in the answer of my previous question, ffmpeg interacts differently, I think the one who knows the answer will be (maybe I’m wrong) someone with experience in ffmpeg.

• ffmpeg based app and VLC IPC ?

  1er avril 2012, par ronag

  I have an application that uses the ffmpeg libraries (not ffmpeg.exe) to encode video and would like to forward the encoded data directly to a VLC process.

  Right now I use udp ://localhost (i.e. avio_open("udp://localhost:5290") and vlc udp://@localhost:5290) for interprocess communication, however it seems a bit unreliable.

  ffmpeg (avio_open) doesn't seem to support named pipes, i.e. \\.\pipe\test is not accepted, and I cannot use standard output/input piping since the applications run in different processes.

  Soo my question is, how can I achieve reliable (and somewhat efficient) interprocess communication between VLC and an application using the ffmpeg libraries ?