HDMI capture script.

hdmi-capture.sh

#!/bin/sh
set -e -u

# Base command used to invoke FFmpeg; run "ffmpeg" with as high a priority as
# possible, and minimize its logging output.
FFMPEG="nice -n 20 ffmpeg -loglevel error -hide_banner"
# These control the format of the audio and video.
DEFAULT_VIDEO_EXTENSION="mkv"

SELF="${0##*/}"

run()
(
    case "$1" in
      --log=.*)     log_file="${1#--log=}"
                    shift
                    echo "$@"
                    exec "$@" > "$log_file" 2>&1 ;;

      *)            echo "$@"
                    exec "$@" ;;
    esac
)

silently()
(
    "$@" >/dev/null 2>&1 || return 0
)

usage()
{
    echo TODO
}

die()
{
    echo "$SELF:" "$@" >&2
    exit 2
}

handle_sigint()
{
    echo && echo "Caught SIGINT; stopping video capture."

    echo "Killing FFmpeg processes:"
    run kill -INT $ffmpeg_pids
    wait

    echo "Combining audio and video streams into a single file:"
    run $FFMPEG -i "$audio_tempfile" -i "$video_tempfile" -codec copy -map 0:a:0 -map 1:v:0 "$destination"
    du -h "$destination"

    run rm "$audio_tempfile" "$video_tempfile" "$ffmpeg_log_file"
    run rmdir "$tempdir"
}

main()
{
    if [ "$#" -gt 1 ] || [ "${1:-}" = "--help" ]; then
        usage
        test "$#" -eq 1 && return || return 2
    elif [ "$#" -eq 0 ] || [ -d "$1" ]; then
        basename="$(date +%Y-%m-%dT%H:%M:%S%z)"
        extension="$DEFAULT_VIDEO_EXTENSION"
        destination="${1+${1%/}/}$basename.$extension"
    else
        destination="$1"
        extension="${destination##*.}"
    fi

    if [ -z "$extension" ] || [ "$extension" = "$destination" ]; then
        die "$destination: destination path does not include an extension"
    fi

    # Make sure FFmpeg does not interpret the paths as URIs or options.
    parent="$(dirname "$destination")"

    case "$parent" in
      [!/]*:*|-*) parent="./$parent" ;;
    esac

    case "$destination" in
      [!/]*:*|-*) destination="./$destination" ;;
    esac

    tempdir=".$SELF.tmp" && test "$parent" = "." || tempdir="$parent/$tempdir"
    ffmpeg_log_file="$tempdir/ffmpeg.log"

    if [ -e "$tempdir" ]; then
        printf "%s: %s already exists; overwrite and continue anyway? (n/Y) " \
               "$SELF" "$tempdir"
        read -r response
        case "$response" in
          *[yY]*)   FFMPEG="$FFMPEG -y" ;;
          *)        return 2 ;;
        esac
    else
        mkdir "$tempdir"
        FFMPEG="$FFMPEG -n"
    fi

    # The video grabber device connects and disconnects constantly for some
    # reason, so the audio and video device identifiers are queried repeatedly
    # until both are found.
    while :; do
        pulse_audio_id="$(
            pactl list short sources \
            | awk '/usb-Video_Grabber_HDMI_to_U3_capture/ { print $1; exit }'
        )"

        video_device="$(
            find /sys/devices/ -type f -name name \
              -exec grep -l -e '^HDMI to U3 capture$' {} + \
            | awk -F "/" '/video4linux/ { print "/dev/" $(NF - 1); exit }'
        )"

        if [ -n "$pulse_audio_id" ] && [ -n "$video_device" ]; then
            break
        elif [ -n "$pulse_audio_id" ]; then
            what="video"
        elif [ -n "$video_device" ]; then
            what="audio"
        else
            what="audio or video"
        fi

        echo "$SELF: unable to find $what device; sleeping then trying again"
        sleep 1
    done

    # Invocation of these FFmpeg processes races against the disconnect, but in
    # practice, FFmpeg is usually able to connect to the device quickly enough
    # that it's rarely a problem.
    > "$ffmpeg_log_file"
    ffmpeg_pids=""

    audio_tempfile="$tempdir/audio.wav"
    run --log="$ffmpeg_log_file" $FFMPEG -f pulse -ac 2 -ar 44100 -i "$pulse_audio_id" -c copy -map 0 "$audio_tempfile" &
    ffmpeg_pids="$ffmpeg_pids $!"

    video_tempfile="$tempdir/video.$extension"
    run --log="$ffmpeg_log_file" $FFMPEG -f v4l2 -i "$video_device" -c copy -map 0 "$video_tempfile" &
    ffmpeg_pids="$ffmpeg_pids $!"

    # If there was a problem invoking FFmpeg, the subprocesses usually die
    # quickly, so wait briefly before checking to see if any invocations
    # failed.
    sleep 1 &&
      if ! kill -0 $ffmpeg_pids; then
        silently kill -INT $ffmpeg_pids
        cat "$ffmpeg_log_file"
        die "unable to start FFmpeg"
    fi

    # Once everything is running, display the size of the captured data until
    # the user stops recording with SIGINT / ^C.
    trap handle_sigint INT
    trap EXIT

    (
        while :; do
            printf "\r%s   " "$(du -h "$tempdir" | tr "\t" " ")"
            sleep 1
        done
    ) || :
}

main "$@"