FFMPEG Recipes

18 February 2024

Not exactly "an FFMPEG cookbook", more like a collection of recipes scrawled on the back of old envelopes.

Extract the audio from a bunch of MPEG-4 movies

for a in *.mp4
do
    ffmpeg -i $a -map 0:1 -codec:a copy $(
        echo $a | sed -e 's/mp4/aac/g'
    )
done

Extract audio from an MPEG-4 stream and re-encode it as MP3

ffmpeg -hide_banner \
    -i ./stream.mp4 \
    -map_metadata -1 -vn ./audio.mp3

Re-encode audio to MP3 with a selected bitrate

for a in $(
    find -name \*.aac
)
do
    ffmpeg -hide_banner -i $a -map_metadata -1 \
        -c:a libmp3lame -ac 2 -b:a 192k $(
            echo $a | sed 's/aac/mp3/'
        )
done

Convert MPEG-4 AVI files to MPEG-4 streams

for a in *.avi
do
    ffmpeg -hide_banner -i $a -map_metadata -1 \
        -codec:v copy -codec:a copy \
        $(echo $a | sed 's/avi/mp4/g')
done

Concatenate 100% compatible videos that have already been split into parts

echo file part1.mp4 > list.txt
echo file part2.mp4 >> list.txt
ffmpeg -f concat -safe 0 -i list.txt \
    -c copy -y output.mp4

Merge video and audio held into 2 MPEG-4 streams into a single MPEG-4 stream

ffmpeg -hide_banner \
    -i ./video.mp4 -i ./audio.mp4 \
    -map_metadata -1 \
    -codec:v copy -codec:a copy \
    ./merged.mp4

Deinterlace, rescale and encode as silent H264/MPEG-4

ffmpeg -i ./original.mp4 \
    -vf yadif -vf scale=720:574 \
    -c:v libx264 -preset slow -crf 0 \
    -an ./processed.mp4

Overlay two video camera streams on top of each other

ffmpeg \
    -f video4linux2 -r 30 -s 640x480 -i /dev/video0 \
    -f video4linux2 -r 30 -s 640x480 -i /dev/video2 \
    -filter_complex "[1]format=yuva444p,colorchannelmixer=aa=0.5[in2];[0][in2]overlay" \
    -y overlaid.mp4

Determine which (video) frames in a soundtrack contain peaks

FPS=25
ffmpeg \
    -i ./soundtrack.wav \
    -af astats=metadata=1:reset=$(
        echo ${FPS} | awk '{ printf 1 / $1 }'
    ),ametadata=print:key=lavfi.astats.Overall.Max_level:file=- \
    -f null /dev/null

Split into chunks each starting on a keyframe

ffmpeg -i ./input.mp4 \
    -acodec copy -format segment -vcodec copy \
    -reset_timestamps 1 \
    -map 0 chunk_%06d.mp4

After the chunks in the previous example have been split, You can copy them into subdirectories and join each subdirectory back into a video with:

AWK='{ print "file " $1; }'

for CHUNK in $(find -type d | grep / | sort)
do
    CHUNK_NUMBER=$(echo $CHUNK | sed -e 's/.\///g')
    LIST_FILE=list_${CHUNK_NUMBER}.txt
    ls ${CHUNK}/*.mp4 | \
        grep mp4 | \
        awk "${AWK}" >${LIST_FILE}
    NEXT_CHUNK=./$((CHUNK_NUMBER + 1))
    if [ -d ${NEXT_CHUNK} ]
    then
        ls ${NEXT_CHUNK}/*.mp4 | \
            head --lines 1 | \
            awk "${AWK}" >${LIST_FILE}
    fi
    ffmpeg -f concat -safe 0 -i ${LIST_FILE} \
        -c copy -y chunk_${CHUNK_NUMBER}.mp4
done

Rescale old-school PAL TV programmes.

Truncate to length of audio or video (whichever is shortest).
Rescale the video to PAL "standard" size.
Take the video quality down to "good enough" for PAL.
Take the audio down to 44.1 mono at a suitable compression rate.

for a in *webm
do
    ffmpeg -hide_banner -i $a -shortest -map_metadata -1 \
        -c:v libx264 -crf 27 \
        -filter:v scale=746x576 -aspect 4:3 \
        -ar 44100 -ac 1 -b:a 64k \
        -y $( echo $a | sed -e 's/webm/mp4/g' )
done