videoencoding.md

Video Encoding

References:

• https://gist.github.com/tayvano/6e2d456a9897f55025e25035478a3a50 -> complete list of ffmpeg flags / commands
• https://gist.github.com/Vestride/278e13915894821e1d6f#gistcomment-3023674 -> good quality gist with informative comments
• https://evilmartians.com/chronicles/better-web-video-with-av1-codec -> the new av1 format

Todos

• Add -movflags +faststart as per https://rigor.com/blog/optimizing-mp4-video-for-fast-streaming ?
• Resarch 2-pass setup also for libx264/mp4
• Explore av1 (se above)

---

mp4 /h264

2k, 8K bitrate, preserve framerate, profile high

ffmpeg  -i [SOURCE] \
  -vf "scale=w=min(iw\,1920):h=-2" \
  -c:v libx264 \
  -profile high \
  -b:v 20000k \
  -pix_fmt yuv420p \
  out2k_8k.mp4

2k, 8K bitrate, 30 framerate, profile high

ffmpeg  -i [SOURCE] \
  -vf "scale=w=min(iw\,1920):h=-2, fps=fps=30" \
  -c:v libx264 \
  -profile:v high \
  -b:v 8000k \
  -pix_fmt yuv420p \
  out2k_30fps_8Mb.mp4

4k, 8K bitrate, 30 framerate, profile high

ffmpeg  -i [SOURCE] \
  -vf "scale=w=min(iw\,3840):h=-2, fps=fps=30" \
  -c:v libx264 \
  -profile:v high \
  -b:v 8000k \
  -pix_fmt yuv420p \
  out4k_30fps_8Mb.mp4

4k, 8K constrained bitrate, 30 framerate

ffmpeg  -i [SOURCE] \
  -vf "scale=w=min(iw\,3840):h=-2, fps=fps=30" \
  -c:v libx264 \
  -b:v 8000k \
  -maxrate 8000k \
  -bufsize 16000k \
  -pix_fmt yuv420p \
  out4k_30fps_8000mbr.mp4

---

Webm / vp9

References

• https://trac.ffmpeg.org/wiki/Encode/VP9
• https://www.webmproject.org/docs/encoder-parameters/
• https://developers.google.com/media/vp9

Alternativ two-pass targeting an average bitrate

result: 24 hour encoding. 6.8MB file. Not good enough quality

ffmpeg -y -i [SOURCE] -an -c:v libvpx-vp9 -pass 1 \
  -b:v 6000k \
  -minrate 3000k \
  -maxrate 8700k \
  -crf 24 \
  -quality best \
  -f webm /dev/null && \
ffmpeg -i [SOURCE] -an -c:v libvpx-vp9 -pass 2 \
  -b:v 6000k \
  -minrate 3000k \
  -maxrate 8700k \
  -crf 24 \
  -quality best \
  -speed 2 \
  -threads 2
  -f webm out-6k-crf24.webm

Constant quality 2-pass

ffmpeg -y -i [SOURCE] \
  -c:v libvpx-vp9 \
  -b:v 0 \
  -pass 1 \
  -an\
   -f webm /dev/null && \
ffmpeg -i [SOURCE] \
  -c:v libvpx-vp9 \
  -b:v 0 \
  -pass 2 \
  -an
  out_avg-br.webm

Initial 2-pass test (too low quality)

1. pass

ffmpeg -y -i [SOURCE] \
  -c:v libvpx-vp9 \
  -pass 1 \
  -b:v 2M \
  -vf "scale=w=min(iw\,1920):h=-2" \
  -crf 30 \
  -speed 4 \
  -an \
  -quality good \
  -f webm  /dev/null

2. pass

ffmpeg -y -i [SOURCE] \
  -c:v libvpx-vp9 \
  -pass 2 \
  -b:v 2M \
  -vf "scale=w=min(iw\,1920):h=-2" \
  -crf 30 \
  -quality good \
  -speed 2 \
  -an \
  -f webm out.webm

---

Thumbnail

References

• https://networking.ringofsaturn.com/Unix/extractthumbnail.php

ffmpeg -i [SOURCE] \
  -an \
  -frames:v 1 \
  -vf "scale=w=1920:h=-1" \
  image.jpg

Optional forced scaling with crop

  -vf "scale=200:100:force_original_aspect_ratio=increase,crop=200:100"

---

Documentation

prop	desc
-an	skip audio
-c:v libx264	codec video
-c:a copy	copies audio (no codec)
-b:vf	video bitrate
-vf	filtergraph
	scale	scaling. See https://trac.ffmpeg.org/wiki/Scaling
		h=-2	(preserve aspec ratio as multiple of 2
		w=min(iw,1920)	input width but not over 1920 (no upscaling)
	fps=fps=30	frame per second in output
-pix_fmt yuv420p	Chroma subsampling: 4:2:0. I have no fucking idea...
-r 24	force the frame rate to 24 fps. (NB: Better to use fps filter)
-y	Overwrite output files without asking.
>>>>>>>>>	For thumbnails
-ss 100	Position
-frames:v 1	Number of frames / images