Makefile to fix broken mp4 files

Makefile

# This makefile finds all .mp4 files and attempts to repair their indexes without re-encoding. 
# It's a makefile so you can use "make -jN" to take advantage of N cores on your computer finish many quickly

MP4:=$(wildcard *.mp4)
OUTDIR:=out
FAST:=$(patsubst %.mp4,${OUTDIR}/%.fast.mp4,${MP4})
REKEYED:=$(patsubst %.mp4,${OUTDIR}/%.rekeyed.mp4,${MP4})

all:
        @echo "Use 'make fast' to do a fast file index rebuild"
        @echo "Use 'make rekeyed' to fix broken or missing frames"

fast: ${FAST}

rekeyed: ${REKEYED}

# create output directory
outdir:
        mkdir -p ${OUTDIR}

# how to create fixed files
${OUTDIR}/%.fast.mp4: %.mp4 outdir
        ffmpeg -i $< -c copy $@

# how to create rekeyed files
${OUTDIR}/%.rekeyed.mp4: %.mp4 outdir
        ffmpeg -i $< -force_key_frames "expr:gte(t,n_forced*3)" $@

clean: 
        rm -rf ${FAST} ${REKEYED}