Converting video with FFmpegCore

Working with multimedia is terra incognita for most of the developers since it's something that one rarely encounters while working with usual business applications. So when I was tasked to convert video for the project I'm currently working on I was expecting to deal with some sort of old poorly maintained C++ library. So FFmpegCore was a pleasant surprise since it enables working with .Net Core which is an area of my expertise.

Examples in this article will be provided in F# which I'm a big fan of but they are pretty straightforward so it should be no problem in translating them to C#.

Installing FFmpeg

While documentation reads that this core is "A .NET Standard FFMpeg/FFProbe wrapper" this tells nothing about the fact that Ffmpeg/fmprobe should be installed on the machine where the application is running.

Furthermore, I think it is worth clarifying that FFMpeg is a cross-platform command-line tool that allows working with video.

While on Linux once you do apt install you're good to go on Windows there is a point of interest. Installing FFmpeg on Windows is a matter of downloading the binaries and putting them in a folder you will but once running the tool you may face the error:

system.componentmodel.win32exception: the system cannot find the the file specified

which is fixed with the help of static class FFMpegOptions

let options = FFMpegOptions()
options.RootDirectory <- "path to your binaries"
FFMpegOptions.Configure(options)

Querying video information

In order to query information about the video, we use static FFProbe which has both synchronous and asynchronous API for video analysis. Let's stick with the async version and serialize the output to examine the wealth of information that FFProbe provides us.

async {
    let! videoInfo = FFProbe.AnalyseAsync fileName |> Async.AwaitTask
    return JsonSerializer.Serialize videoInfo
}

The output may be as rich a below

{
   "Path":"D:\\giphy.mp4",
   "Extension":".mp4",
   "Duration":{
      "Ticks":17200000,
      "Days":0,
      "Hours":0,
      "Milliseconds":720,
      "Minutes":0,
      "Seconds":1,
      "TotalDays":1.990740740740741E-05,
      "TotalHours":0.00047777777777777776,
      "TotalMilliseconds":1720,
      "TotalMinutes":0.028666666666666667,
      "TotalSeconds":1.72
   },
   "Format":{
      "Duration":{
         "Ticks":17200000,
         "Days":0,
         "Hours":0,
         "Milliseconds":720,
         "Minutes":0,
         "Seconds":1,
         "TotalDays":1.990740740740741E-05,
         "TotalHours":0.00047777777777777776,
         "TotalMilliseconds":1720,
         "TotalMinutes":0.028666666666666667,
         "TotalSeconds":1.72
      },
      "FormatName":"mov,mp4,m4a,3gp,3g2,mj2",
      "FormatLongName":"QuickTime / MOV",
      "StreamCount":1,
      "ProbeScore":100,
      "BitRate":458339,
      "Tags":{
         "major_brand":"isom",
         "minor_version":"512",
         "compatible_brands":"isomiso2avc1mp41",
         "encoder":"Lavf56.40.101"
      }
   },
   "PrimaryAudioStream":null,
   "PrimaryVideoStream":{
      "AvgFrameRate":25,
      "BitsPerRawSample":8,
      "DisplayAspectRatio":{

      },
      "Profile":"Constrained Baseline",
      "Width":480,
      "Height":264,
      "FrameRate":25,
      "PixelFormat":"yuv420p",
      "Rotation":0,
      "Index":0,
      "CodecName":"h264",
      "CodecLongName":"H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
      "BitRate":453744,
      "Duration":{
         "Ticks":17200000,
         "Days":0,
         "Hours":0,
         "Milliseconds":720,
         "Minutes":0,
         "Seconds":1,
         "TotalDays":1.990740740740741E-05,
         "TotalHours":0.00047777777777777776,
         "TotalMilliseconds":1720,
         "TotalMinutes":0.028666666666666667,
         "TotalSeconds":1.72
      },
      "Language":"und",
      "Tags":{
         "language":"und",
         "handler_name":"VideoHandler",
         "vendor_id":"[0][0][0][0]"
      }
   },
   "VideoStreams":[
      {
         "AvgFrameRate":25,
         "BitsPerRawSample":8,
         "DisplayAspectRatio":{

         },
         "Profile":"Constrained Baseline",
         "Width":480,
         "Height":264,
         "FrameRate":25,
         "PixelFormat":"yuv420p",
         "Rotation":0,
         "Index":0,
         "CodecName":"h264",
         "CodecLongName":"H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
         "BitRate":453744,
         "Duration":{
            "Ticks":17200000,
            "Days":0,
            "Hours":0,
            "Milliseconds":720,
            "Minutes":0,
            "Seconds":1,
            "TotalDays":1.990740740740741E-05,
            "TotalHours":0.00047777777777777776,
            "TotalMilliseconds":1720,
            "TotalMinutes":0.028666666666666667,
            "TotalSeconds":1.72
         },
         "Language":"und",
         "Tags":{
            "language":"und",
            "handler_name":"VideoHandler",
            "vendor_id":"[0][0][0][0]"
         }
      }
   ],
   "AudioStreams":[

   ]
}