Merge branch 'dev'

vision/ffmpeg.md

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+# 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
+