SMPTE master clock#

Playback rate can be controlled through a master clock, following the LTC encoding. The timecode is received through an audio input, which by default is the default audio input of the computer (basically, the line in or the microphone input). The timecode is an audio file which can be generated by a number of softwares, among which Ardour and the command line utility ltcgen.

Using ltcgen (installed from the sources or from a package), one can create an audio file containing the timecode with the following comand:

# Generate a 1 minute timecode
ltcgen -t 00:00 -l 00:01:00:00 /tmp/timecode.wav

This timecode can be played from another computer which output is connected to the input of the Splash computer. It can also be played locally using the Jack audio server. Ensure that Jack and mplayer are installed:

sudo apt install jackd mplayer

The following commands will run the jackd server, and run mplayer with the previously generated audio file:

jackd -R -d alsa &
mplayer -ao jack:name=mplayer /tmp/timecode.wav -loop 0

Lastly, Splash must be set to read the timecode from Jack instead of the default audio input. To do so, you have to set the Audio input device option from the Main GUI tabulation, and set it to mplayer (which is the name we give to the Jack source in the previous command line).

Splash should now receive the timecode from mplayer. As a command line tool, mplayer can be paused with the space bar, and seeked with the arrow keys. In Splash, the current time code can be seen in the Timings panel of the GUI.

To terminate the Jack server, type the following command:

killall jackd