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• ffmpeg run from c# Process not closing when using '-i anullsrc'

  1er octobre 2022, par Brown Bear

  I am generating a large collection MP4 videos from an OpenGL source. This has worked perfectly so far but I recently noticed that some TV media player don't like video without audio, see here for more info.

  


  So far i hve been using the following code :

  


      private bool StartRecording()
    {
        _ffmpeg = new Process();
        _ffmpeg.StartInfo.FileName = "ffmpeg.exe";
        _ffmpeg.StartInfo.Arguments = $"-f rawvideo -pix_fmt rgba -s {RecordSize.Width}x{RecordSize.Height} -r 30 -i - -c libx264 -crf 17 -pix_fmt yuv420p -b:v 1024k -bufsize:v 1835008 {RecordFile} -tune animation";
        _ffmpeg.StartInfo.RedirectStandardInput = true;
        _ffmpeg.Start();

        if(_ffmpeg.HasExited)
        {
            IsRecording = false;
            return false;
        }
        return true;
    }

    private void RecordFrame(RenderUpdate update)
    {
        if (_ffmpeg == null)
            return;

        var frame = Project.RecordFrame(update);
        var data = new byte[frame.Length];
        var height = RecordSize.Height;
        var width = RecordSize.Width;

        for (var k = 0; k < height; k++)
        {
            var j = height - k - 1;
            Buffer.BlockCopy(
                frame, k * width * 4,
                data, j * width * 4,
                width * 4);
        }

        _ffmpeg.StandardInput.BaseStream.Write(data, 0, data.Length);
    }

    private void StopRecording()
    {
        Project.StopRecording();
        if (_ffmpeg == null)
            return;

        _ffmpeg.StandardInput.Flush();
        _ffmpeg.StandardInput.Close();
        _ffmpeg.Close();
        _ffmpeg.Dispose();
    }


  


  And it has worked perfectly until I modified the 'ffmpeg' cmd line arguments to include '-i anullsrc' for the audio.

  


    _ffmpeg.StartInfo.Arguments = $"-f rawvideo -pix_fmt rgba -s {RecordSize.Width}x{RecordSize.Height} -r 30 -i - -f lavfi -i anullsrc=channel_layout=mono:sample_rate=8k -c:v libx264 -crf 17 -pix_fmt yuv420p -b:v 1024k -bufsize:v 1835008 {RecordFile} -tune animation";


  


  The moment I add '-f lavfi -i anullsrc' to the cmd line the call to 'StopRecording()' has no effect and ffmpeg continues to run.

  


  I can manually stop it by closing the console window or even using ctrl-c, but the job needs to be automated so this is just not an option.

  


  Ultimately my question is Why is ffmpeg behaving this way ?

  


  I've come up with a couple of work arounds, but I don't like either :

  


  

  1. Post process the videos as per the link I mentioned earlier. Not practical. I need to generate 1000s of videos and a single batch of 350 takes around 6 hours. 50% of that time is consumed by ffmpeg encoding, so to re-encode them all just to add a null audio track would nearly double the time.

  


  2. Try to push a 'ctrl-c' through to the ffmpeg process as per this post. I did some quick tests with 'GenerateConsoleCtrlEvent' without sucess, and the idea of having to manually start and stop the Process via 'kernel32.dll' seems excessive not to mention old school.

  


  


  Any insight would be greatly appreciated.

  


• Desktop recording with ffmpeg won't play in anything but VLC

  12 mai 2022, par Alex

  I'm creating a desktop application for fun/education. Its primary function is to record my PCs screen and have a pretty UI to play this back. I am recording with ffmpeg like so :

  


  ffmpeg -thread_queue_size 1024 -f gdigrab -framerate 50 -video_size 1920x1080 -i desktop -f dshow -i audio="virtual-audio-capturer" -r 50 -preset fast -c:v h264_nvenc -qp 23 "D:/vid.mp4"


  


  At first glance this seems fine, a file is created and playing it back in VLC media player also works fine.

  


  The problem is that I can't play this back in anything else. Windows apps (videos + media player) just freeze up/provide no clue as to the problem. My end goal is to embed this into a HTML5 player to fit with the electron/react framework I'm writing my application in. This also doesn't play in a similar fashion.

  


  I ran mediainfo on the file in WSL and got the following :

  


  General
Complete name                            : vid.mp4
Format                                   : MPEG-4
Format profile                           : Base Media
Codec ID                                 : isom (isom/iso2/avc1/mp41)
File size                                : 544 MiB
Duration                                 : 1 min 15 s
Overall bit rate mode                    : Variable
Overall bit rate                         : 60.4 Mb/s
Writing application                      : Lavf59.10.100

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High 4:4:4 Predictive@L4.2
Format settings                          : 1 Ref Frames
Format settings, CABAC                   : No
Format settings, Reference frames        : 1 frame
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1 min 15 s
Bit rate mode                            : Variable
Bit rate                                 : 60.3 Mb/s
Maximum bit rate                         : 2 000 kb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 50.000 FPS
Color space                              : RGB
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.581
Stream size                              : 543 MiB (100%)
Color range                              : Full
Matrix coefficients                      : Identity
Codec configuration box                  : avcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 1 min 15 s
Source duration                          : 1 min 15 s
Bit rate mode                            : Constant
Bit rate                                 : 132 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz


  


  I also saw this thread (ffmpeg created timelapse won’t play on other players than VLC) suggesting the bit rate may be the problem but having tried the suggestions there had no luck.

  


  At a glance I suspected the "Codec ID" field as with comparison to other MP4 files that windows does play it is slightly different, i.e. :

  


  isom (isom/iso2/avc1/mp41) vs mp42 (mp42/mp41/isom/avc1)

  


  However fiddling with the ffmpeg encoder settings I managed to vary this and still could not play the video back.

  


  Also including the ffprobe output :

  


  ffprobe version 4.2.4-1ubuntu0.1 Copyright (c) 2007-2020 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
  configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'vid.mp4:
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf59.10.100
  Duration: 00:01:15.50, start: 0.000000, bitrate: 60414 kb/s
    Stream #0:0(und): Video: h264 (High 4:4:4 Predictive) (avc1 / 0x31637661), gbrp(pc, gbr/unknown/unknown), 1920x1080 [SAR 1:1 DAR 16:9], 60277 kb/s, 50 fps, 50 tbr, 12800 tbn, 100 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 132 kb/s (default)
    Metadata:
      handler_name    : SoundHandler


  


• How to batch process a series of video files with powershell and other-transcode/ffmpeg

  7 juin 2022, par DarkDiamond

  TL ;DR

  


  What did I do wrong in the following PowerShell-Script ? It does not work as expected.

  


  ---

  


  I am recording some of my lectures in my university with a photo camera. This works pretty well although I have to split the single lecture into three to four parts because the camera can only record 29 minutes of video in one take. I know that this is a common issue related to some licensensing problem that most photo cameras simply don't have the right license to record longer videos. But it confronts me with the problem that I later have to edit the files together after I did some post processing on them.

  


  With the camera I produce up to four video files with sizes around 3.5 GB which is way to big in order to be of any use because our IT department understandably doesn't want to host so much data, as I produce around 22 GB of video material each week.

  


  Some time ago I came across a very useful tool called "other-video-transcoding" by Don Melton over on GitHub, written in ruby, that allows me to compress the files to a reasonable file size without any visual loss. In addition I crop the videos to remove the part of each frame that is neither the board nor a place where my professor stands in order to decrease the filesize even further and do some privacy protection by cutting out most of the students.

  


  As the tools are accessable via the command line, it is relatively easy to configure and does not cost additional computational power to render a nice gui, so I can edit one of the 29 minute clips in less than 10 minutes.

  


  Now I wanted to optimize my workflow by writing a PowerShell script that only takes the parameters what to crop and which files to work on and then does the rest on its own so I can just start the script and then do something else while my laptop renders the new files.

  


  So far I have the following :

  


  $video_path = Get-ChildItem ..\ -Directory | findstr "SoSe"

Get-ChildItem $video_path -name | findstr ".MP4" | Out-File temp.txt -Append 
Get-Content temp.txt | ForEach-Object {"file " + $_} >> .\files.txt

Get-ChildItem $video_path |
Foreach-Object {
other-transcode --hevc --mp4 --target 3000 --crop 1920:780:0:0 $_.FullName
}

#other-transcode --hevc --mp4 --crop 1920:720:60:0 ..\SoSe22_Theo1_videos_v14_RAW\
ffmpeg -f concat -i files.txt -c copy merged.mp4
Remove-Item .\temp.txt


  


  but it does not quite do what I it expect to do.
This is my file system :

  


  sciebo/
└── SoSe22_Theo1_videos/
    ├── SoSe22_Theo1_videos_v16/
    │   ├── SoSe22_Theo1_videos_v16_KOMPR/
    │   │   ├── C0001.mp4
    │   │   ├── C0002.mp4
    │   │   ├── C0003.mp4
    │   │   ├── C0004.mp4
    │   │   ├── temp.txt
    │   │   ├── files.txt
    │   │   └── merged.mp4
    │   └── SoSe22_Theo1_videos_v16_RAW/
    │       ├── C0001.mp4
    │       ├── C0002.mp4
    │       ├── C0003.mp4
    │       └── C0004.mp4
    └── SoSe22_Theo1_videos_v17/
        ├── SoSe22_Theo1_videos_v17_KOMPR
        └── SoSe22_Theo1_videos_v17_RAW/
            ├── C0006.mp4
            ├── C0007.mp4
            ├── C0008.mp4
            └── C0009.mp4


  


  where the 16th lecture is already processed and the 17th is not. I always have the raw video data in the folders ending on RAW and the edited/compressed output files in the one ending on KOMPR. Note that the video files in the KOMPR folder are the output files of the other-transcode tool.

  


  The real work happens in the line where it says

  


  other-transcode --hevc --mp4 --target 3000 --crop 1920:780:0:0 $_.FullName


  


  and in the line

  


  ffmpeg -f concat -i files.txt -c copy merged.mp4


  


  where I concat the output files into the final version I can upload to our online learning platform.
What is wrong with my script ? In the end I'd like to pass the --crop parameter just to my script, but that is not the primary problem.

  


  ---

  


  A little information on the transcoding script so you don't have to look into the documentation :
  
As the last argument the tool takes the location of the video files to work on, be it relative or absolute file paths. The output is placed in the folder the script is called in, so if I cd into one of the KOMPR directories and then call

  


  other-transcode --mp4 ../SoSe22_Theo1_videos_v16_RAW/C0001.mp4


  


  a new file C0001.mp4 is created in the KOMPR directory and the transcoded video and old audio are written to that new video file.