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• How to properly escape shell arguments on Windows ?

  20 novembre 2016, par PeeHaa

  I am trying to properly escape user supplied data for a command line script. Normally I would use escapeshellarg, however this will simply not work because it’s breaks the eventual command line in glorious ways.

  The use case is trying to add meta data to videos using ffmpeg. A simplified and isolated problem case is the following command :

  ffmpeg -i in.mp4 -metadata author="My Name" out.mp4

  The author value is user supplied (My Name). I tried escaping only the user supplied part which resulted in :

  ffmpeg -i in.mp4 -metadata author=""My Name"" out.mp4

  Which results in the following ffmpeg error :

  Name : Invalid argument

  Next I tried escaping the entire flag (-metadata author="My Name") which results in :

  ffmpeg -i in.mp4 "-metadata author= My Name " out.mp4

  "Unrecognized option ’metadata author= My Name ’.

  Test cases :

  $flag = '-metadata author="%s"';
  
  
  
  var_dump(sprintf($flag, escapeshellarg('My Name')));
  
  var_dump(escapeshellarg(sprintf($flag, 'My Name')));

  Is there anything that will properly escape the user supplied data so that users cannot pass arbitrary flags to my command and that will make ffmpeg happy without having to do it manually with the risk of forgetting something and screwing it up ?

  Update

  I also tried escaping the entire flag value which works unless there is a double quote inside the user supplied part :

  $flag = 'author="%s"';
  
  
  
  var_dump('-metadata ' . escapeshellarg(sprintf($flag, 'My Name')));
  
  var_dump('-metadata ' . escapeshellarg(sprintf($flag, 'My "Name"')));

  Which results in :

  -metadata "author= My Name "
  
  -metadata "author= My  Name  " // it eats my quotes

• How to convert a Stream on the fly with FFMpegCore ?

  18 octobre 2023, par Adrian

  For a school project, I need to stream videos that I get from torrents while they are downloading on the server.
When the video is a .mp4 file, there's no problem, but I must also be able to stream .mkv files, and for that I need to convert them into .mp4 before sending them to the client, and I can't find a way to convert my Stream that I get from MonoTorrents with FFMpegCore into a Stream that I can send to my client.

  


  Here is the code I wrote to simply download and stream my torrent :

  


  var cEngine = new ClientEngine();

var manager = await cEngine.AddStreamingAsync(GenerateMagnet(torrent), ) ?? throw new Exception("An error occurred while creating the torrent manager");

await manager.StartAsync();
await manager.WaitForMetadataAsync();

var videoFile = manager.Files.OrderByDescending(f => f.Length).FirstOrDefault();
if (videoFile == null)
    return Results.NotFound();

var stream = await manager.StreamProvider!.CreateStreamAsync(videoFile, true);
return Results.File(stream, contentType: "video/mp4", fileDownloadName: manager.Name, enableRangeProcessing: true);


  


  I saw that the most common way to convert videos is by using ffmpeg. .NET has a package called FFMpefCore that is a wrapper for ffmpeg.

  


  To my previous code, I would add right before the return :

  


  if (!videoFile.Path.EndsWith(".mp4"))
{
    var outputStream = new MemoryStream();
    FFMpegArguments
        .FromPipeInput(new StreamPipeSource(stream), options =>
        {
            options.ForceFormat("mp4");
        })
        .OutputToPipe(new StreamPipeSink(outputStream))
        .ProcessAsynchronously();
    return Results.File(outputStream, contentType: "video/mp4", fileDownloadName: manager.Name, enableRangeProcessing: true);
}


  


  I unfortunately can't get a "live" Stream to send to my client.

  


• Find video resolution and video duration of remote mediafile

  22 février 2012, par osgx

  I want to write an program which can find some metainformation of mediafile. I'm interested in popular video formats, such as avi, mkv, mp4, mov (may be other popular too). I want basically to get :

  • Video size (720, 1080, 360 etc)
  • Total runtime of video (may be not very exact)
  • Number of audio streams
  • Name of video codec
  • Name of audio codec

  There is already the mediainfo, but in my program I want to get information about remote file, which may be accessed via ftp, http, samba ; or even torrent (there are some torrent solutions, which allows to read not-yet downloaded file).

  MediaInfo library have no support of samba (smb ://) and mkv format (for runtime).

  Also, I want to know, how much data should be downloaded to get this information. I want not to download full videofile because I have no enough disk space.

  Is this information in the first 1 or 10 or 100 KiloBytes of the file ? Is it at predictable offset if I know the container name and total file size ?

  PS : Platform is Linux, Language is C/C++