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• Reusing FFMPEG AVFilterGraph

  11 avril 2022, par Sapozhnikov Andrey

  In my code I apply same filtering on multiple input files. In first version of code I created AVFilterGraph for every input, but I think these actions might be excessive.
  
However, when I try to reuse the same graph, I face with the error during sending frame to abuffer filter. At the previous iteration over input files, I passed EOF to it for flushing, and the av_buffersrc_add_frame function has a check for this :

  


  BufferSourceContext *s = ctx->priv;
...
if (s->eof)
    return AVERROR(EINVAL);


  


  which crashes the execution on the second iteration.
Unfortunately, I couldn't find any functions that can restore buffer filter or something like that.

  


  I would like to know if avfilter implies the possibility to reuse once created filter graph, or there are some fundamental misconceptions in my understanding of ffmpeg logic by passing input after EOF.

  


  Thank you !

  


• ffmpeg scaled output resolution is off by 1px for non-standard inputs [duplicate]

  14 janvier 2023, par GROVER.

  I'm using the ffmpeg CLI to scale user-submitted videos :

  


  ffmpeg -i path/to/file -vf scale=1920:-2 -c:v libx264 -r 30 output.mp4


  


  The scaling works fine with standard video sizes, such as 1920×1080 and 720×480. However, once we start using videos that do not have conventional resolutions, the output begins to scale incorrectly.

  


  For example, a video that has a resolution of 3360×1882 will output to 1921×1076, when the expected resolution should theoretically be : 1920×1075.

  


  Now, obviously ffmpeg is attempting to account for that remaining .42857px on the height, but I'd prefer it just get cropped off instead (doesn't matter if it's from the top or bottom).

  


  How would I go about doing this safely for every video ?

  


  For bonus points, how do I make it swap scaling depending on if the height is greater than the width (and vice versa). For example, if the video has a ratio of 2:1, it scales using a height of 1080px instead of a width of 1920px.

  


• How to capture display and stream to an RGB led matrix with FFMPEG

  16 avril 2019, par AdminBenni

  I am trying to use FFMPEG to capture a raspberry pi’s screen/display and stream it to an RGB led matrix but cannot figure out how to capture the screen/display properly.

  I am working with an example program (provided by Adafruit) that takes a video file as a parameter and streams it to the matrix and I’m trying to effectively swap out any mention of the video file with the screen/display.
  Here’s the code

  I tried to change line 141 as follows.

  // Before
  
  if(avformat_open_input(&pFormatCtx, movie_file, NULL, NULL)!=0)
  
      return -1; // Couldn't open file
  
  
  
  // After
  
  AVInputFormat *pAVInputFormat = NULL;
  
  pAVInputFormat = av_find_input_format("x11grab");
  
  if(avformat_open_input(&pFormatCtx,, ":0.0+10,250", pAVInputFormat, NULL))
  
      return -1; // Couldn't open file

  But that didn’t really seem to work.

  Is there an easy way to make the program capture from the screen/display instead of a video file ?