Add -ipc option to control gpu-screen-recorder over a unix domain socket

The socket accepts the same commands as the signal handlers, except that
saving a replay takes an arbitrary number of seconds instead of only the
fixed times that the signals provide. Requests and replies are newline
terminated json objects and every request is replied to, parsed with the
sj.h json library that was added to external.
Requests are handled on a thread that only runs while the recorder
exists, so the recorder control fields are now atomics, which they have
to be now that another thread writes them.

1 files changed, 4 insertions, 1 deletions

diff --git a/README.md b/README.md
index 953e1c1..089076e 100644
--- a/README.md
+++ b/README.md
@@ -138,7 +138,10 @@ This way of recording while using replay/streaming is more efficient than runnin
 To save a video in replay mode, you need to send signal SIGUSR1 to gpu screen recorder. You can do this by running `pkill -SIGUSR1 -f "^gpu-screen-recorder"`.\
 To stop recording send SIGINT to gpu screen recorder. You can do this by running `pkill -SIGINT -f "^gpu-screen-recorder"` or pressing `Ctrl-C` in the terminal that runs gpu screen recorder. When recording a regular non-replay video this will also save the video.\
 To pause/unpause recording send SIGUSR2 to gpu screen recorder. You can do this by running `pkill -SIGUSR2 -f "^gpu-screen-recorder"`. This is only applicable and useful when recording (not streaming nor replay).\
-There are more signals to control GPU Screen Recorder. Run `gpu-screen-recorder --help` to list them all (under `NOTES` section).
+There are more signals to control GPU Screen Recorder. Run `gpu-screen-recorder --help` to list them all (under `NOTES` section).\
+GPU Screen Recorder can also be controlled with json messages over a unix domain socket by launching it with the `-ipc` option, for example `-ipc "$XDG_RUNTIME_DIR/gsr.sock"`.
+This gives the same control as the signals, except that a replay can be saved with an arbitrary number of seconds, for example `echo '{"id":1,"name":"save-replay","data":30}' | socat - "UNIX-CONNECT:$XDG_RUNTIME_DIR/gsr.sock"`.
+See the `IPC` section in the man page (`man gpu-screen-recorder`) for the full protocol.
 ## Simple way to run replay without gui
 Run the script `scripts/start-replay.sh` to start replay and then `scripts/save-replay.sh` to save a replay and `scripts/stop-replay.sh` to stop the replay. The videos are saved to `$HOME/Videos`.
 You can use these scripts to start replay at system startup if you add `scripts/start-replay.sh` to startup (this can be done differently depending on your desktop environment / window manager) and then go into