[LAU] Toggle Jack Transport CLI

[hollundertee at gmx.net]

On Wed, 16 Nov 2016 07:04:04 +0000
holger at dehnhardt.org wrote:

> Hi lista :)
> 
> 	Using an i3 (https://i3wm.org/docs/userguide.html#exec)
> shortcut, I can control my jack transport from everywhere, even when
> no jack application has focus :
> 
> 	bindsym $mod+p exec echo play | jack_transport
> bindsym $mod+Shift+p exec echo stop | jack_transport
> 
> 	Thanks to FalkTX for the pipe trick BTW, I saw that on
> linuxmusicians ; This is very cool if you have some sort of wireless
> keyboard, but as you can see it's two different keystrokes, how do I
> make it so  toggles play/pause? Alternatively, how do I know when
> jack transport is rolling, so I can hack my way into making my own
> toggle script? I did my homework and read the inline --help of all
> the available jack commands on my machine : With this patch,
> jack_transport should be able to toggle. I will suggest it to the
> jack-develop list but would be happy if some else can test it. Holger
> 
> -----------------
> 
> diff --git a/example-clients/transport.c b/example-clients/transport.c
> index c543b41..0b1130f 100644
> --- a/example-clients/transport.c
> +++ b/example-clients/transport.c
> @@ -211,6 +211,29 @@ static void com_timeout(char *arg)
>  jack_set_sync_timeout(client, (jack_time_t) (timeout*1000000));
> }
> +/* Set sync timeout in seconds. */
> +static void com_toggle(char *arg)
> +{ 
> + jack_position_t current;
> + jack_transport_state_t transport_state;
> +
> + transport_state = jack_transport_query (client, ¤t);
> +
> + switch (transport_state) {
> + case JackTransportStopped:
> + com_play( arg );
> + break;
> + case JackTransportRolling:
> + com_stop( arg );
> + break;
> + case JackTransportStarting:
> + printf ("state: Starting - no transport toggling");
> + break;
> + default:
> + printf ("state: Unknown - no transport toggling");
> + } 
> +}
> +
> /* Command parsing based on GNU readline info examples. */
> @@ -238,6 +261,7 @@ command_t commands[] = {
>  {"stop", com_stop, "Stop transport"},
>  {"tempo", com_tempo, "Set beat tempo "},
>  {"timeout", com_timeout, "Set sync timeout in "},
> + {"toggle", com_toggle, "Toggle transport rolling"},
>  {"?", com_help, "Synonym for `help'" },
>  {(char *)NULL, (cmd_function_t *)NULL, (char *)NULL }
> };


Thanks guys,

I was just browsing the list for nice Linux Audio music when I found
this thread, which is just what I needed as well :)
In my case the purpose is for screencasts.
I plan to record the screen using SimpleScreenRecorder and audio
through jack into Ardour or somesuch. The problem I had was that if I
start SSR and Ardour separately I need to manually align A/V later. It
is simpler if A/V starts at the same time.

I was thinking of starting jack transport through qjackctl or somesuch,
using the CLI did not occur to me.

SSR lacks jack transport control, but I think assigning the same hotkey
to SSR and jack transport should work just fine. I guess I still need
to take the alsa/jacks latency into account, but at least that should
be small and constant.

Does anyone have a better idea?

@Holger: Thanks, but patching a jack example client requires
maintenance since this change would be lost with each new jack package
coming through the repo.

Regards,
Philipp