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• Generating Gif from Mp4 directly - ffmpeg

  20 janvier 2016, par senty

  I am trying to generate a gif from an mp4 video file. I want to scale it and crop it while generating.

  I achieved that (cropping & scaling) from mp4 to mp4 with the below line , (so I can extract pngs with ffmpeg and use Imagick to make animated gif), but I believe there is a better way of achieving purely with ffmpeg.

  ffmpeg -i in.mp4 -filter:v "scale=300:ih*300/iw, crop=200:500:50:80" -c:a copy out.mp4

  My question is how to achieve the same this code is doing, but for directly generating gif from mp4.

  ---

  Then I started tweaking with mp4 to gif conversion, but when palette comes in, I couldn’t fully understand what’s going on.

  I found this answer and I made it work, however I couldn’t understand how to adapt scaling & cropping.

  $ ffmpeg -y -ss 30 -t 3 -i in.mp4 \
-vf fps=10,scale=320:-1:flags=lanczos,palettegen palette.png

  $ ffmpeg -ss 30 -t 3 -i in.flv -i palette.png -filter_complex \ "fps=10,scale=320:-1:flags=lanczos[x];[x][1:v]paletteuse" out.gif

  I partially understand what this bit does -y -ss 30 -t 3 -i in.mp4 (getting the first 30 seconds and generating a 3 second gif out of it). But for the next lines, I am completely lost what it is actually doing.

  It’d be amazing if someone can explain what each command does, or refer a link explaining this topic.

• How do I write a simple script which calls ffmpeg and records an audio stream ?

  29 janvier 2016, par user2192778

  I would like to write a script which calls ffmpeg and begins recording an internet radio stream.

  This command is simple :
  ffmpeg -i http://myaudiostream.com output.mp3

  I understand how to make a .bat file, I just don’t know specifically how to code these instructions.

  Can I have some help ?
  I haven’t written a script before, though I understand how it works. I don’t know any of the syntax.

• ffmpeg - AVPixelFormat, what is "smaples" means in the documentation ?

  17 juin 2017, par dafnahaktana

  I did not understand the documentation , for example :

  AV_PIX_FMT_YUV422P planar YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples) 

  I didn’t understand the meaning of "(1 Cr & Cb sample per 2x1 Y samples) ",
  and what does it mean 4:2:2 ? I could not find explanation anywhere.

  Also , I see there are types like AV_PIX_FMT_YUV420P that have 12bpp. Does that mean that each pixel is represented by 12 bit ? if so, how is it represented ? Should I allocate two bytes for each pixel and ignore the last 4 bits ? or I should allocate something like ceil((#pixels)*1.5) bytes ?