mplayer slave: set volume before starting the playback
I know this is about a specific program (mplayer back-end); however it will be used to program a front-end so I hope it is still considered on-topic on Stack Overflow.
I want to run two mplayer slave instances which will be used to fade between different audio streams (webradio; smoothly change the channel). To do this, I set the "software volume" of mplayer so it will not affect the PCM output channel of the sound card but insert a software volume mixer to adjust the volume.
However, I encounter the following problem.
I start mplayer with the following command (can be tested on command-line):
mplayer -slave -idle -softvol
and send the following commands to mplayer:
loadfile <url>
set volume 0
it starts (for a short time) to play the file at 100% volume and then jumps to 0% volume. If I swap the two commands, mplayer tells me that I can't adjust the volume:
Failed to set property 'volume' to '0'.
ANS_ERROR=PROPERTY_UNAVAILABLE
Obviously, the audio filter isn't yet loaded / audio output not yet set up or something like that, so mplayer can't change the volume of a non-existing audio output.
Can I force mplayer to initialize everything in advance so that I can set the volume to 0%, load the file and then increase the volume to fade in the playback?
I already checked whether I can set the volume after playing some file (e.g. a silent dummy file); mplayer complains with the same error. For now, the only option I can think of is to start such a dummy file, adjust the volume, stop the dummy file, load the correct file to be played, and it will start with the volume just set. But I can't believe this is the best option.
Answer
I solved the problem by myself: While I tried to follow this guide, -af volume=0 didn't help. However, there also is a -volume 0 command line option which worked for me:
mplayer -slave -idle -softvol -volume 0