Edit reStream.sh and README

README.md

@@ -10,8 +10,14 @@ reMarkable screen sharing over SSH.
 ## Installation
 
 1. Clone this repository: `git clone https://github.com/rien/reStream`.
-2. (Optional but recommended) [Install lz4 on your host and reMarkable](#sub-second-latency).
+2. Install `lz4` on your host with your usual package manager. On Ubuntu,
+`apt install liblz4-tool` will do the trick.
 3. [Set up an SSH key and add it to the ssh-agent](https://help.github.com/en/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent), then add your key to the reMarkable with `ssh-copy-id root@10.11.99.1`.
+4. Copy the `restream` executable to the reMarkable and make it executable.
+    ```
+    # scp restream.arm.static root@10.11.99.1:/home/root/restream
+    # ssh root@10.11.99.1 'chmod +x /home/root/restream'
+    ```
 
 ## Usage
 
@@ -27,7 +33,7 @@ reMarkable screen sharing over SSH.
 - `-s --source`: the ssh destination of the reMarkable (default: `root@10.11.99.1`)
 - `-o --output`: path of the output where the video should be recorded, as understood by `ffmpeg`; if this is `-`, the video is displayed in a new window and not recorded anywhere (default: `-`)
 - `-f --format`: when recording to an output, this option is used to force the encoding format; if this is `-`, `ffmpeg`’s auto format detection based on the file extension is used (default: `-`).
-- `-w --webcam`: record to a video4linux2 web cam device. By default the first found web cam is taken, this can be overwritten with `-o`. The video is scaled to 1280x720 to ensure compatibility with MS Teams, Skype for business and other programs which need this specific format.
+- `-w --webcam`: record to a video4linux2 web cam device. By default the first found web cam is taken, this can be overwritten with `-o`. The video is scaled to 1280x720 to ensure compatibility with MS Teams, Skype for business and other programs which need this specific format. See [video4linux loopback](#video4linux-loopback) for installation instructions.
 - `-m --measure`: use `pv` to measure how much data throughput you have (good to experiment with parameters to speed up the pipeline)
 - `-t --title`: set a custom window title for the video stream. The default title is "reStream". This option is disabled when using `-o --output`
 
@@ -41,24 +47,7 @@ On your **host** machine:
 - ssh
 - Video4Linux loopback kernel module if you want to use `--webcam`
 
-On your **reMarkable** nothing is needed, unless you want...
-
-### Sub-second latency
-
-To achieve sub-second latency, you'll need [lz4](https://github.com/lz4/lz4)
-on your host and on your reMarkable.
-
-You can install `lz4` on your host with your usual package manager. On Ubuntu,
-`apt install liblz4-tool` will do the trick.
-
-On your **reMarkable** you'll need a binary of `lz4` build for the arm platform,
-you can do this yourself by [installing the reMarkable toolchain](https://remarkablewiki.com/devel/qt_creator#toolchain)
-and compiling `lz4` from source with the toolchain enabled, or you can use the
-statically linked binary I have already built and put in this repo.
-
-Copy the `lz4` program to your reMarkable with
-`scp lz4.arm.static root@10.11.99.1:/home/root/lz4`, make it executable with
-`ssh root@10.11.99.1 'chmod +x /home/root/lz4'` and you're ready to go.
+On your **reMarkable** you need the `restream` binary (see [installation instructions](#installation)).
 
 ### Video4Linux Loopback
 
@@ -89,3 +78,7 @@ The result should contain a line with "platform:v4l2loopback".
 Steps you can try if the script isn't working:
 - [Set up an SSH key](#installation)
 - Update `ffmpeg` to version 4.
+
+## Development
+
+If you want to play with the `restream` code, you will have to [install Rust](https://www.rust-lang.org/learn/get-started) and [setup the reMarkable toolchain](https://github.com/canselcik/libremarkable#setting-up-the-toolchain) to do cross-platform development.

reStream.sh

@@ -92,42 +92,14 @@ case "$rm_version" in
     "reMarkable 1.0")
         width=1408
         height=1872
-        bytes_per_pixel=2
         pixel_format="rgb565le"
-        # calculate how much bytes the window is
-        window_bytes="$((width * height * bytes_per_pixel))"
-        # read the first $window_bytes of the framebuffer
-        head_fb0="dd if=/dev/fb0 count=1 bs=$window_bytes 2>/dev/null"
+        transpose=0
         ;;
     "reMarkable 2.0")
         pixel_format="gray8"
         width=1872
         height=1404
-        bytes_per_pixel=1
-
-        # calculate how much bytes the window is
-        window_bytes="$((width * height * bytes_per_pixel))"
-
-        # find xochitl's process
-        pid="$(ssh_cmd pidof xochitl)"
-        echo "xochitl's PID: $pid"
-
-        # find framebuffer location in memory
-        # it is actually the map allocated _after_ the fb0 mmap
-        read_address="grep -C1 '/dev/fb0' /proc/$pid/maps | tail -n1 | sed 's/-.*$//'"
-        skip_bytes_hex="$(ssh_cmd "$read_address")"
-        skip_bytes="$((0x$skip_bytes_hex + 8))"
-        echo "framebuffer is at 0x$skip_bytes_hex"
-
-        # carve the framebuffer out of the process memory
-        page_size=4096
-        window_start_blocks="$((skip_bytes / page_size))"
-        window_offset="$((skip_bytes % page_size))"
-        window_length_blocks="$((window_bytes / page_size + 1))"
-
-        # Using dd with bs=1 is too slow, so we first carve out the pages our desired
-        # bytes are located in, and then we trim the resulting data with what we need.
-        head_fb0="dd if=/proc/$pid/mem bs=$page_size skip=$window_start_blocks count=$window_length_blocks 2>/dev/null | tail -c+$window_offset | head -c $window_bytes"
+        transpose=1
         ;;
     *)
         echo "Unsupported reMarkable version: $rm_version."
@@ -137,33 +109,23 @@ case "$rm_version" in
 esac
 
 # technical parameters
-loop_wait="true"
 loglevel="info"
+decompress="lz4 -d"
 
-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"
+# check if lz4 is present on the host
+if ! lz4 -V >/dev/null; then
+   echo "Your host does not have lz4."
+   echo "Please install it using the instruction in the README:"
+   echo "https://github.com/rien/reStream/#installation"
+   exit 1
 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 ! lz4 -V >/dev/null; then
-    echo "Your host does not have lz4."
-    fallback_to_gzip
-else
-    decompress="lz4 -d"
+# check if restream binay is present on remarkable
+if ssh_cmd "[ ! -f ~/restream ]"; then
+    echo "The restream binary is not installed on your reMarkable."
+    echo "Please install it using the instruction in the README:"
+    echo "https://github.com/rien/reStream/#installation"
+    exit 1
 fi
 
 # use pv to measure throughput if desired, else we just pipe through cat
@@ -186,7 +148,8 @@ video_filters=""
 set --
 
 # rotate 90 degrees if landscape=true
-$landscape && video_filters="$video_filters,transpose=1"
+$landscape && transpose="$((transpose + 1))"
+[ $transpose != 0 ] && video_filters="$video_filters,transpose=$transpose"
 
 # Scale and add padding if we are targeting a webcam because a lot of services
 # expect a size of exactly 1280x720 (tested in Firefox, MS Teams, and Skype for
@@ -200,9 +163,6 @@ fi
 # set each frame presentation time to the time it is received
 video_filters="$video_filters,setpts=(RTCTIME - RTCSTART) / (TB * 1000000)"
 
-# loop that keeps on reading and compressing, to be executed remotely
-read_loop="while $head_fb0; do $loop_wait; done | $compress"
-
 set -- "$@" -vf "${video_filters#,}"
 
 if [ "$output_path" = - ]; then
@@ -222,7 +182,7 @@ fi
 set -e # stop if an error occurs
 
 # shellcheck disable=SC2086
-ssh_cmd "$read_loop" \
+ssh_cmd "./restream" \
     | $decompress \
     | $host_passthrough \
     | "$output_cmd" \