make MP4 files stream better by moving their "moov" atom to the front

faststart

#!/bin/sh
# script to make mp4 videos start fast 
# (i.e. shifting their moov atoms to the front)

FNAME=$1
[ -f "$FNAME" ] || exit 1

TMPFNAME=`mktemp -u ${FNAME}.XXXXXX`

head -c128 "$FNAME" | grep -F moov -q
IS_FAST=$?

if [ $IS_FAST -eq 1 ]; then
        ffmpeg -hide_banner -i "$FNAME" -c:v copy -c:a copy -movflags \+faststart -f mp4 "$TMPFNAME" && \
                touch -r "$FNAME" "$TMPFNAME" && \
                mv -f "$TMPFNAME" "$FNAME"
fi