#!/bin/bash                                                                                                                                                     
########################################################################
# This was SUPPOSED to be a quick hack to ffmpeg-convert videos, but
# ffmpeg overheats my CPUs, pegging them at 95-100C, unless i run it
# through cpulimit, leading to much more code.

function die(){
    local rc=$1
    shift
    echo "Error: $@" 1>&2
    exit $rc
}

[[ x = "x$1" ]] && {
    die 1 "Usage: $0 video_files..."
}
ffmpeg=$(which ffmpeg 2>/dev/null)
[[ x = "${ffmpeg}x" ]] && {
    die 127 "cannot find ffmpeg in the PATH"
}
# Problem: ffmpeg is heating all 4 of my cores to 95-99C.
# So... we'll throttle it with cpulimit.
cpulimit=$(which cpulimit 2>/dev/null)
[[ x = "${cpulimit}x" ]] && {
    die 127 "cannot find cpulimit in the PATH"
}
limitpct=150 # percent of CPU to limit to via $cpulimit.
# ^^^^^^ 60% keeps my 4 cores all under 50C. It slows down conversion
# by about 75-80%, though :/.
# 75% provides better (not great) performance and all CPUs under 60C.
# 85% keeps all CPUs under 60C.
# 100% performs only marginally better than 60% and keeps the CPUs at
# about 55-65C.
# 200% keeps the CPUs between 70-75C (hot enough to engage my loud
# fans).

for file in "$@"; do
    [[ -e "$file" ]] || die 127 "file not found: $file"
    out="${file%.*}.mp4"
    [[ "$file" = "$out" ]] && die 126 "Input and output file would have the same name: $file"
    echo "=> Transcoding [$file] ==> [$out] ... "
    # reminder: ffmpeg -y option is necessary in conjunction with
    # cpulimit to work around some weird timing bug, where ffmpeg
    # reports $out as already existing.
    "${cpulimit}" -f -l ${limitpct} -- "$ffmpeg" -y -i "$file" "$out" || die $? "ffmpeg error code $?"
    touch --reference="$file" "$out"
    ls -lh "$file" "$out"
    echo
done
echo "Done!"