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• Ffmpeg - Generate VTT File From Sprite, Using Spatial Media Fragment

  20 octobre 2019, par David

  Hi I am looking to create a .VTT file from a sprite that i have generated using Ffmpeg.

  Ffmpeg command :

   $"-i {inputMediaFile} -vf \"select = not(mod(n\\, 30)),scale = 120:80,tile = 7x7\" -an -vsync 0 {outputMediaFile}"

  This selects every 30th frame, and then scales it to 120x80 pixels and creates 8x8 tiles in the output image.

  I would like to make a .VTT from the generated image in C#, so i know the height and width of my individual images in the sprite (120x80) and there is 64 images in total in the output image.

  From this i need to produce a VTT like this :

  WEBVTT
  
  
  
  1
  
  00:00:00.000 --> 00:00:01.000
  
  test-00001.jpg#xywh=0,0,120,80
  
  
  
  2
  
  00:00:01.000 --> 00:00:02.000
  
  test-00001.jpg#xywh=120,0,120,80
  
  
  
  3
  
  00:00:02.000 --> 00:00:03.000
  
  test-00001.jpg#xywh=240,0,120,80
  
  
  
  4
  
  00:00:03.000 --> 00:00:04.000
  
  test-00001.jpg#xywh=360,0,120,80
  
  
  
  5
  
  00:00:04.000 --> 00:00:05.000
  
  test-00001.jpg#xywh=480,0,120,80
  
  
  
  6
  
  00:00:05.000 --> 00:00:06.000
  
  test-00001.jpg#xywh=600,0,120,80
  
  
  
  7
  
  00:00:06.000 --> 00:00:07.000
  
  test-00001.jpg#xywh=720,0,120,80
  
  
  
  8
  
  00:00:07.000 --> 00:00:08.000
  
  test-00001.jpg#xywh=840,0,120,80
  
  
  
  9
  
  00:00:08.000 --> 00:00:09.000
  
  test-00001.jpg#xywh=0,80,120,80

  There is also situations when there is n amount of sprite files.

  Im hoping there may be a library out there that can handle this, or even better if i can keep it contained within Ffmpeg - based on Ffmpeg docs i dont think this is possible though.

  Thanks in advance if anyone as any ideas, its doable as ive seen Nodejs and Ruby examples.

• How to fade video using a custom curve function in ffmpeg ?

  2 avril 2018, par Zoltan

  I would like to fade out a video using a different transition curve than what the fade filter uses (which is probably linear).

  For audio, I can easily choose from a wide variety of curves that the afade filter provides, or I can supply a custom expression to the volume filter, like (sin(PI/2 * min(1\, max(-1\, 1/2 * (t - 3)))) + 1)/2. For video, however, I could not find similar possibilities.

  Based on its description, it seems to me that the geq filter could be misused to achieve this, but I couldn’t get it to work. Additionally, it is very slow, probably because it works on individual pixels, even though the expression only depends on time.

• Splitting odd and even frames in Gstreamer

  4 avril 2014, par user3498379

  I am building an application whereby I need to split a videostream(RTSP/MJPEG) into individual frames. The extracted frames then need to be put into two named pipes. I need to alternate the frames between two named pipes, i.e. even frames go to pipe one and odd frames go to pipe 2. I have been able to achieve this with ffmpeg using the following command :

  ffmpeg -i "rtsp://<ipaddress>/axis-media/media.amp?videocodec=jpeg" -vf select="mod(n-1\,2)" -vcodec mjpeg -f avi -y  -vf select="not(mod(n-1\,2))" -vcodec mjpeg -f avi -y 
  
  </ipaddress>

  However I have run into an RTP packet size issue with ffmpeg when using large resolutions e.g. 2048x1536. My question is ; is there a gstreamer equivalent command ? I have the basic gstreamer command which extracts images :

   gst-launch rtspsrc location=rtsp://<ipaddress>/axis-media/media.amp?videocodec=jpeg ! decodebin2 ! jpegenc ! multifilesink location="frame%d.jpg"
  
  </ipaddress>

  But now I need the additional piece, any help will be much appreciated.