restream/reStream.sh

#!/bin/sh

# default values for arguments
ssh_host="root@10.11.99.1" # remarkable connected trough USB
landscape=true             # rotate 90 degrees to the right

# loop through arguments and process them
while [ $# -gt 0 ]; do
    case "$1" in
        -p | --portrait)
            landscape=false
            shift
            ;;
        -d | --destination)
            ssh_host="$2"
            shift
            shift
            ;;
        *)
            echo "Usage: $0 [-p] [-d <destination>]"
            exit 1
            ;;
    esac
done

# technical parameters
width=1408
height=1872
bytes_per_pixel=2
loop_wait="true"
loglevel="info"

ssh_cmd() {
    ssh -o ConnectTimeout=1 "$ssh_host" "$@"
}

# check if we are able to reach the remarkable
if ! ssh_cmd true; then
    echo "$ssh_host unreachable"
    exit 1
fi

fallback_to_gzip() {
    echo "Falling back to gzip, your experience may not be optimal."
    echo "Go to https://github.com/rien/reStream/#sub-second-latency for a better experience."
    compress="gzip"
    decompress="gzip -d"
    sleep 2
}

# check if lz4 is present on remarkable
if ssh_cmd "[ -f /opt/bin/lz4 ]"; then
    compress="/opt/bin/lz4"
elif ssh_cmd "[ -f ~/lz4 ]"; then
    compress="\$HOME/lz4"
fi

# gracefully degrade to gzip if is not present on remarkable or host
if [ -z "$compress" ]; then
    echo "Your remarkable does not have lz4."
    fallback_to_gzip
elif ! which lz4; then
    echo "Your host does not have lz4."
    fallback_to_gzip
else
    decompress="lz4 -d"
fi

# calculte how much bytes the window is
window_bytes="$((width * height * bytes_per_pixel))"

# rotate 90 degrees if landscape=true
landscape_param="$($landscape && echo '-vf transpose=1')"

# read the first $window_bytes of the framebuffer
head_fb0="dd if=/dev/fb0 count=1 bs=$window_bytes 2>/dev/null"

# loop that keeps on reading and compressing, to be executed remotely
read_loop="while $head_fb0; do $loop_wait; done | $compress"

set -e # stop if an error occurs

# shellcheck disable=SC2086
ssh_cmd "$read_loop" \
    | $decompress \
    | ffplay \
        -vcodec rawvideo \
        -loglevel "$loglevel" \
        -f rawvideo \
        -pixel_format gray16le \
        -video_size "$width,$height" \
        $landscape_param \
        -i -