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• High Quality Screen Capture with FFmpeg

  18 novembre 2015, par plumzl

  I’m trying to figure out a command for high quality screen capture on REHL.

  I have tried various options, but none really worked. The quality is not good enough. I’m quite new to ffmpeg and doesn’t quite understand all the different flags. So any help would be appreciated !

  The commands I have tried :

  ffmpeg -y -f x11grab -r 30 -s 1920x1080 -i :0.0+0,0 -vcodec libx264 -strict -2 -b:v 16M output.mov

  The first command I tried. The weird thing is it doesn’t seem to preserve the bitrate specified -b:v 16M. The output video’s bitrate is only 2mb/s. Is that not the correct way to specify bitrate when doing screen capture ?

  ffmpeg -f x11grab -s 1920x1080 -r 30 -i :0.0 -qscale 0 -vcodec huffyuv output.mov

  The huffyuv codec is supposed to be lossless, but the quality doesn’t seem to be any better than the libx264 output.

  ffmpeg -f x11grab -r 30 -s 1920x1080 -i :0.0+0,0 -vcodec copy -pix_fmt yuv420p -qscale 0 -an output.mkv
  
  ffmpeg -f rawvideo -pix_fmt yuv420p -s:v 1920x1080 -r 30 -i output.mkv -an -c:v libx264 -qscale 0 result.mov 

  I’m even trying to capture rawvideo and then convert it to libx264 codec viedeo. But the output is corrupted.

  I’m using the version of ffmpeg that’s built on April 23rd this year. It doesn’t have the preset like -vpre lossless_ultrafast which I see mentioned in a lot posts.

  Edit :

  After more research, this is the command I end up using. I have to use h264 codec and yuv420p as pixel_fmt since I need to be able to play the quicktimes using quicktime.

  ffmpeg -y -f x11grab -framerate 30 -video_size 1920x1080 -i :0.0+0,0 -c:v libx264 -pix_fmt yuv420p -qp 0 -preset ultrafast output.mov

  The quality doesn’t seem to be much improved even though -qp is set to 0. But it could also because of the rgb conversion to yuv color space according to this post.

  https://trac.ffmpeg.org/wiki/Encode/H.264

• fluent-ffmpeg throwing SIGSEGV in nodejs

  22 mars 2023, par C G

  I am using fluent-ffmpeg to resize a video, split into frames, etc.
Here's my code :

  


  ffmpeg("./uploads/video.mp4")
    .output("./uploads/small-video.mp4")
    .noAudio()
    .size('320x?')
    .on('end', function() {
        extractVideoFrames("./uploads/small-video.mp4")
    })
    .run()


  


  I am getting a SIGSEGV error, which I suspect might be because of some weird memory issue ?
Here's the error :

  


  Error: ffmpeg was killed with signal SIGSEGV&#xA;    at ChildProcess.<anonymous> (/home/admin/superformweb/node_modules/fluent-ffmpeg/lib/processor.js:180:22)&#xA;    at ChildProcess.emit (node:events:513:28)&#xA;    at ChildProcess._handle.onexit (node:internal/child_process:291:12)&#xA;Emitted &#x27;error&#x27; event on FfmpegCommand instance at:&#xA;    at emitEnd (/home/admin/superformweb/node_modules/fluent-ffmpeg/lib/processor.js:424:16)&#xA;    at /home/admin/superformweb/node_modules/fluent-ffmpeg/lib/processor.js:433:16&#xA;    at wrapper (/home/admin/superformweb/node_modules/async/dist/async.js:271:20)&#xA;    at next (/home/admin/superformweb/node_modules/async/dist/async.js:5795:24)&#xA;    at /home/admin/superformweb/node_modules/async/dist/async.js:327:20&#xA;    at wrapper (/home/admin/superformweb/node_modules/async/dist/async.js:271:20)&#xA;    at next (/home/admin/superformweb/node_modules/async/dist/async.js:5795:24)&#xA;    at /home/admin/superformweb/node_modules/async/dist/async.js:327:20&#xA;    at /home/admin/superformweb/node_modules/fluent-ffmpeg/lib/capabilities.js:519:16&#xA;    at handleExit (/home/admin/superformweb/node_modules/fluent-ffmpeg/lib/processor.js:170:11)&#xA;&#xA;</anonymous>

  


  I have installed ffmpeg first : sudo apt-get install ffmpeg
Then I installed node packages :

  


  npm install ffmpeg
npm install fluent-ffmpeg


  


• Could there be an unexpected collision of MS VC runtimes ?

  25 mai 2016, par sharpener

  I have learned the hard way, it’s not very good to share heap pointers between two dlls who each depends on different MS VC runtime. Fair enough. Based on this experience and current weird behavior of a program chain being debugged I would like to ask a

  Question :

  Could lib1.dll using one runtime (eg. msvcrt.dll) possibly damage heap of lib2.dll using different runtime (eg. vcruntime140d.dll) ? No pointers shared, just pairs of malloc/free on the same runtime.

  Background : (for those who would ask for it)

  • I have standard zeranoe ffmpeg libraries dependent on msvcrt.dll.
  • I created small C dll covering required functionality based on those ffmpeg libs, let’s call it libvideo.dll. It’s dependent on VS2015 runtime.
  • I created libvideosharp.dll a managed C# wrapper library (also VS2015) for libvideo.dll (marshalling).
  • I created C# test app using the libvideosharp.dll (also VS2015).
  • Debugging the C# test app (and associated libraries in the chain) I experience following :
    1. libvideo.dll mallocs and inits a data structure.
    2. libvideo.dll calls some ffmpeg init routines (av_register_all, avformat_network_init) which might malloc on its own runtime.
    3. libvideo.dll’s data structure is corrupted (not even passed to ffmpeg libs in any way, just independent malloced block).