lk/sound/ffmpeg.md
2022-01-18 13:24:25 +01:00

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---
title: "ffmpeg"
tags: [ "Documentation", "sound" ]
---
# Basics
ffmpeg -i [input file] output_file.mkv
The input file might be a device, such as a camera.
Play video:
> ffplay file.mp4
#Record screen
Take the format as 'grab the x11 screen'.
> ffmpeg -f x11grab -s [screensize] -i :0.0 out.mkv
Get screensize with
> xrandr -q
or maybe just...
> ffmpeg -f x11grab -s "$(xdpyinfo | grep dimensions | awk '{print $2}')" -i :1.0 out.mkv
#Add default pulse audio
> ffmpeg -f x11grab -s [screensize] -i :0.0 -f alsa -i default out.mkv
For problems, see pavucontrol.
# Random online suggestion
ffmpeg -video_size "$(xdpyinfo | grep dimensions | awk '{print $2}')" -f x11grab -i :0.0 -f pulse -ac 2 -i default ~/out.mkv
# Rotate
> ffmpeg -i in.mov -vf "transpose=1" out.mov
0 = 90 Counterclockwise and verfical flip (default)
1 = 90 Clockwise
2 = 90 CounterClockwise
3 = 90Clockwise and vertical flip
# Lower Video Quality
A crf quality of 18 is high, while 24 is low quality.
ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4
# convert
Check for supported formats:
> ffmpeg -formats
To convert from mkv to mp4 we can use a codec rather than proper conversion. Both are wrappers around other formats, so this conversion loses less quality than other conversion types.
> ffmpeg -i LostInTranslation.mkv -codec copy LostInTranslation.mp4
Opus to mp3
> ffmpeg -i song.opus song.mp3
> ffmpeg -i video.flv video.mpeg
> ffmpeg -i input.webm -qscale 0 output.mp4
# Video to Audio
> ffmpeg -i input.mp4 -vn output.mp3
# Convert all mkv files to mp4
> for i in *.mkv; do
> ffmpeg -i "$i" -codec copy "${i%.*}.mp4"
> done
# Change resolution
> ffmpeg -i input.mp4 -filter:v scale=1280:720 -c:a copy output.mp4
Or just crop:
> ffmpeg -i input.mp4 -filter:v "crop=w:h:x:y" output.mp4
Or aspect ratio:
> ffmpeg -i input.mp4 -aspect 16:9 output.mp4
Or trim to start and stop times:
> ffmpeg -i input.mp4 -ss 00:00:50 -codec copy -t 50 output.mp4
Indicate start times with -ss and time with -t in seconds.
Or split a video into parts:
> ffmpeg -i input.mp4 -t 00:00:30 -c copy part1.mp4 -ss 00:00:30 -codec copy part2.mp4
# Compress Video
> ffmpeg -i input.mp4 -vf scale=1280:-1 -c:v libx264 -preset veryslow -crf 24 output.mp4
# Extract Images from Video
-r sets the frame rate, and -f selects the format.
> ffmpeg -i input.mp4 -r 1 -f image2 image-%2d.png
# Add Images to Audio
> $ ffmpeg -loop 1 -i inputimage.jpg -i inputaudio.mp3 -c:v libx264 -c:a aac -strict experimental -b:a 192k -shortest output.mp4
# Create a Video from Multiple Parts
First make a text file indicating all the parts, e.g.
```
file /home/sk/myvideos/part1.mp4
file /home/sk/myvideos/part2.mp4
file /home/sk/myvideos/part3.mp4
file /home/sk/myvideos/part4.mp4
```
Then join with:
> ffmpeg -f concat -i join.txt -c copy output.mp4
# Add Subtitles
> fmpeg -i input.mp4 -i subtitle.srt -map 0 -map 1 -c copy -c:v libx264 -crf 23 -preset veryfast output.mp4