Allow choosing the video output

Instead of simply playing back the frames through `ffplay`, I thought it
might be interesting to be able to record the sequence to a video file
or to use it as part of a stream.

I have in mind the use case of making educational videos/live streams
where the tablet can be used as a kind of remote blackboard by teachers,
which is especially relevant currently. But there are certainly other
use cases!

Changes
=======

This commit adds two new options to that effect:

* `-o --output`: Path of the output as understood by `ffmpeg` (usually a
file name). If this is `-` (as it is by default), the existing behavior
of playing the stream through `ffplay` is restored.

* `-f --format`: When recording to an output, this option can be used to
force the encoding format. If this is `-` (again, the default),
`ffmpeg`’s auto format detection is used (based on the file extension).

Because of the possible confusion between the newly added `--output`
option and the existing `--destination` option for specifying the source
address, I suggest renaming the `--destination` option to `--source`
(this is implemented in this commit).

Examples
========

Record to a file
----------------

```sh
./reStream.sh -o remarkable.mp4
```

Caveat: The recorded file plays back too fast.
I am not sure how to fix this.

Create an UDP MPEG-TS stream
----------------------------

```sh
./reStream.sh -o "udp://127.0.0.1:1234" -f "mpegts"
```

This sends frames over UDP to the specified port using the MPEG-TS
format (see <https://trac.ffmpeg.org/wiki/StreamingGuide>). This stream
can then be connected, for example, to OBS for live streaming (see
<https://connect.ed-diamond.com/Linux-Pratique/LP-096/Enrichir-sa-diffusion-de-contenus-multimedias-avec-OBS>
in French).

README.md

@@ -20,7 +20,9 @@ reMarkable screen sharing over SSH.
 ### Options
 
 - `-p --portrait`: shows the reMarkable screen in portrait mode (the default is landscape mode, 90 degrees rotated tot the right)
-- `-d --destination`: the ssh destination of the reMarkable (default: `root@10.11.99.1`)
+- `-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: `-`).
 
 If you have problems, don't hesitate to [open an issue](https://github.com/rien/reStream/issues/new) or [send me an email](mailto:rien.maertens@posteo.be).
 

reStream.sh

@@ -1,8 +1,10 @@
 #!/bin/sh
 
 # default values for arguments
-ssh_host="root@10.11.99.1" # remarkable connected trough USB
+ssh_host="root@10.11.99.1" # remarkable connected through USB
 landscape=true             # rotate 90 degrees to the right
+output_path=-              # display output through ffplay
+format=-                   # automatic output format
 
 # loop through arguments and process them
 while [ $# -gt 0 ]; do
@@ -11,13 +13,23 @@ while [ $# -gt 0 ]; do
             landscape=false
             shift
             ;;
-        -d|--destination)
+        -s|--source)
             ssh_host="$2"
             shift
             shift
             ;;
+        -o|--output)
+            output_path="$2"
+            shift
+            shift
+            ;;
+        -f|--format)
+            format="$2"
+            shift
+            shift
+            ;;
         *)
-            echo "Usage: $0 [-p] [-d <destination>]"
+            echo "Usage: $0 [-p] [-s <source>] [-o <output>] [-f <format>]"
             exit 1
     esac
 done
@@ -66,11 +78,13 @@ fi
 
 
 
-# calculte how much bytes the window is
+output_args=()
+
+# calculate 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')"
+$landscape && output_args+=('-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"
@@ -78,14 +92,27 @@ 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"
 
+if [ "$output_path" = - ]; then
+    output_command=ffplay
+else
+    output_command=ffmpeg
+
+    if [ "$format" != - ]; then
+        output_args+=('-f' "$format")
+    fi
+
+    output_args+=("$output_path")
+fi
+
 set -e # stop if an error occurs
 
 $ssh_cmd "$read_loop" \
     | $decompress \
-    | ffplay -vcodec rawvideo \
+    | "$output_command" \
+             -vcodec rawvideo \
              -loglevel "$loglevel" \
              -f rawvideo \
              -pixel_format gray16le \
              -video_size "$width,$height" \
-             $landscape_param \
-             -i -
+             -i - \
+             "${output_args[@]}"