Writing to mplayer's stdin from bash script.

firewalker · 2010-08-28 11:28:25

I was just fulling with some bash script in order to automate the listening of my favorite radio stations via mplayer and a bash script. Going through the mplayers manual I saw the option -slave.

-slave

This option switches on slave mode. This is intended for use of MPlayer as a backend to other programs. Instead of intercepting keyboard events, MPlayer will read simplistic command lines from its stdin. The section SLAVE MODE PROTOCOL explains the syntax.

At first I thought "ok, easy". I made some tries like "mplayer -slave -quiet .... < /tmp/stdin &" and then something like "echo -e 'mute' > /tmp/stdin" but it wouldn't work.

Is it possible to send a process to the background inside a bash script and then write to it's stdin?

SLAVE MODE PROTOCOL

If the -slave option is given, playback is controlled by a line-based protocol. Each line must contain one command otherwise one of the following tokens:

Commands

        seek <value> [type=<0/:1/:2>]
            Seek to some place in the movie. Type 0 is a relative seek of +/:- <value> seconds. Type 1 seek to <value> % in the movie. Type 2 is a seek to an absolute position of <value> seconds. 
        audio_delay <value>
            Adjust the audio delay of value seconds 
        quit
            Quit MPlayer 
        pause
            Pause/:unpause the playback 
        grap_frames
            Somebody know ? 
        pt_step <value> [force=<value>]
            Go to next/:previous entry in the playtree. 
        pt_up_step <value> [force=<value>]
            Like pt_step but it jumps to next/:previous in the parent list. 
        alt_src_step <value>
            When more than one source is available it selects the next/:previous one (only supported by asx playlist). 
        sub_delay <value> [abs=<value>]
            Adjust the subtitles delay of +/:- <value> seconds or set it to <value> seconds when abs is non zero. 
        osd [level=<value>]
            Toggle osd mode or set it to level when level > 0. 
        volume <dir>
            Increase/:decrease volume 
        [contrast|brightness|hue|saturation] <-100-100> [abs=<value>]
            Set/:Adjust video parameters. 
        frame_drop [type=<value>]
            Toggle/:Set frame dropping mode. 
        sub_visibility
            Toggle subtitle visibility. 
        sub_pos <value>
            Adjust subtitles position. 
        vo_fullscreen
            Switch to fullscreen mode. 
        tv_step_channel <dir>
            Select next/:previous tv channel. 
        tv_step_norm
            Change TV norm. 
        tv_step_chanlist
            Change channel list. 
        gui_[loadsubtitle|about|play|stop]

karol · 2010-08-28 11:41:00

Try https://bbs.archlinux.org/viewtopic.php?id=93952

firewalker · 2010-08-28 11:56:21

Yes it worked just fine for mplayer. Thanks you.

mkfifo is the way to go for other programs too?

karol · 2010-08-28 12:00:32

firewalker wrote:

Yes it worked just fine for mplayer. Thanks you.
mkfifo is the way to go for other programs too?

I think 'man mkfifo' will answer that question :-)

dmz · 2010-08-28 15:44:32

FIFO's are awesome and can be (ab)used for a lot of cool stuff.

I've written some applications that do just what you are trying to do ( http://github.com/trapd00r/rmcd and http://github.com/trapd00r/RPD ), if you need inspiration.

As for the backgrounding - you want to make a 'daemon', to detach from the running shell. See man fork, man 3 setsid and man 3 wait / man 3 waitpid (or my daemonize() function).

firewalker · 2010-08-28 16:25:25

Thanks you very much!!!

Arch Linux

#1 2010-08-28 11:28:25

Writing to mplayer's stdin from bash script.

#2 2010-08-28 11:41:00

Re: Writing to mplayer's stdin from bash script.

#3 2010-08-28 11:56:21

Re: Writing to mplayer's stdin from bash script.

#4 2010-08-28 12:00:32

Re: Writing to mplayer's stdin from bash script.

#5 2010-08-28 15:44:32

Re: Writing to mplayer's stdin from bash script.

#6 2010-08-28 16:25:25

Re: Writing to mplayer's stdin from bash script.

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