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• ffmpeg xfade custom transition expression - Fetch pixel value at specifc x, y from vid1, vid2 ?

  25 janvier 2021, par jsaluja

  I am using xfade with transition=custom, and trying to build expression.
I am referring to official documentation https://ffmpeg.org/ffprobe-all.html#xfade

  


  Per my understanding, expression should return pixel value of merged video

  


  I built a few custom transitions using expressions that return some combination of A, B

  


  For eg.,

  


  "custom:expr='if(gt(P, abs(X/W - 0.5)), A, B)'"
"custom:expr='lerp(A, B, 1 - P)'"


  


  For the next set of transitions, I want to fetch the pixel values from source, target video at specific positions, and combine them in my expressions

  


  I tried using a0(X, Y), b0(X, Y) etc inside of

  


  xfade=transition=custom:expr='r....


  


  I ran into exceptions with ffmpeg complaining it doesn't understand the expression.

  


  Can someone clarify, how i can fetch pixel values as specific position from source, target video and combine them in expression ?

  


• Xamarin Mac FFmpeg launch path not accessible

  25 mars 2024, par Tecnopresley

  I have a Xamarin Forms project with Mac support and I am trying to implement FFmpeg, so I have downloaded the Static build from its official page and added it as in the resources folder of the Mac project with the build action in Content, then I have created a service that will basically remove the audio from a video that I indicate in a path with a FFmpeg command, to do the service I have based on the following answer and I have adapted it to C # :
https://stackoverflow.com/a/37422688/8496520

  


  The problem is that when I try to execute the command I get the following error :

  


  "NSInvalidArgumentException: launch path not accessible"


  


  And I can't find out why this happens, I use the following code in the service (The error occurs when calling the Launch () method of the NSTask) :

  


  public void ExecuteFFmpeg()
{
    try
    {
        var launchPath = NSBundle.MainBundle.PathForResource("ffmpeg", ofType: "");
        var compressTask = new NSTask();
        compressTask.LaunchPath = launchPath;
        compressTask.Arguments = new string[] {
            "-i",
            "downloads/test.mp4",
            "-c",
            "copy",
            "-an",
            "nosound.mp4" };
        compressTask.StandardInput = NSFileHandle.FromNullDevice();
        compressTask.Launch();
        compressTask.WaitUntilExit();
    }
    catch (Exception ex)
    {

    }


  


• compile own ffmpeg filter

  20 juin 2023, par lfk

  I'm trying compile my own ffmpeg filter using official tutorial. My filter uses C++ code. I made header file and adapted my C++ function definition for C. Now I'm trying compile with command make -j<libavfilter> ffmpeg</libavfilter>, but receiving an error message

  


  


  gcc -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat
-Llibavresample -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,—as-needed -Wl,-z,noexecstack -Wl,—warn-common -Wl,-rpath-link=libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil:libavresample
-o ffmpeg_g fftools/ffmpeg_opt.o fftools/ffmpeg_filter.o fftools/ffmpeg_hw.o fftools/cmdutils.o fftools/ffmpeg.o -lavdevice
-lavfilter -lavformat -lavcodec -lswresample -lswscale -lavutil -lm -pthread -lm -lm -lz -pthread -lm -lz -lm -lm -pthread -lm libavfilter/libavfilter.a(vf_foobar.o) : In function `filter_frame' :
/home/joeyes/ffmpeg_sources/ffmpeg/libavfilter/vf_foobar.c:302 :
undefined reference to MyFunction.c
collect2 : ld returned 1 exit status
*** [ffmpeg_g] Error 1

  


  


  For compilation I added OBJS-$(CONFIG_FOOBAR_FILTER) += vf_foobar.o MyCode.o to /libavfilter/makefile

  


  Also I put MyCode.h & MyCode.cpp to /libavfilter folder