[MPlayer-users] SIGCONT causes fast-forward effect

[Pete Nesbitt]

On Sun, 07 Dec 2008 08:31:15 +0100
Oliver Seitz <info at vtnd.de> wrote:

> Am 07.12.2008, 02:54 Uhr, schrieb Pete Nesbitt <pete at linux1.ca>:
> 
> > Hi,
> > I have a bash based cgi script set which uses mplayer in a while
> > loop that runs as a bg process. It passes values from a form based
> > web page (via POST). I use SIGSTOP & SIGCONT for pause and resume
> > functions.
> >
> > When I click 'resume' and the mplayer loop is un-paused, it seems to
> > want to fast forward to where it should be in time. So if you pause
> > it for one minute, then resume, it sounds like it is on fast
> > forward for a second or so, until it is where it would have been in
> > the song had the process not been frozen. Then everything plays
> > normally.
> >
> > Here is the relevant part of the code:
> > pressing pause runs:
> >  kill -s SIGSTOP `/sbin/pidof mplayer` &> /dev/null
> >
> > pressing resume runs:
> >  kill -s SIGCONT `/sbin/pidof mplayer` &> /dev/null
> >
> > (I have tried removing the stdout/err redirs as well)
> >
> > Here is the mplayer loop. Note the bg call after 'done' putting the
> > entire loop in the background via a previous iteration of the
> > script (via a cgi call to 'play').
> >
> >  while read TRACK
> >   do
> >     # snipped some 'now playing' status tracking etc
> >
> >    ${MPLAYER} -quiet ${TRACK} < /dev/null &> /dev/null
> >
> >     # snipped some 'now playing' status tracking etc
> >    let TRACK_NUM=TRACK_NUM+1
> >   done < ${PLAY_LIST} &> /dev/null &
> >
> > The player needs to be in the background, so I don't think there is
> > a way to pass a keystroke to a process running in the bg of a
> > different shell.
> >
> > I can reproduce it at the cli with this, which just replicates the
> > cgi POST: (then run SIGSTOP etc from a diff shell (same user))
> >
> > QueryString="song=%2Fdata%2Fmedia%2Fmusic%2Falbums%2FGenesis%2FNursery_Cryme-72_1.flac%3C%2Ftd"
> > export QueryString
> > ./cm_playing-cgi.sh
> >
> > However, not using the cgi, it is fine, just SIGSTOP mplayer, then
> > SIGCONT (diff shell) it works as expected. (note the line wraps!)
> >
> > mplayer /data/media/music/albums/Genesis/Nursery_Cryme-72_1.flac
> > < /dev/null &> /dev/null &
> >
> >
> > As a wild guess I would say that mplayer is not aware it is paused
> > at the process level (related to being in a bg'd while-loop??), so
> > when it is resumed it tries to catch up to where the system clock or
> > some timer says it should be. I'm thinking I need to tell it not to
> > sync to the real time, but just carry on.
> >
> > Does anyone have any ideas what causes this and how I can prevent
> > it?
> 
> Hi Pete,
> 
> have you tried slave mode to tell mplayer nicely to pause playing
> instead of pulling the emergency brake and releasing it again?
> 
> Greets,
> Kiste
> _______________________________________________
> MPlayer-users mailing list
> MPlayer-users at mplayerhq.hu
> https://lists.mplayerhq.hu/mailman/listinfo/mplayer-users

Hi Kiste,
I tried adding it into the mplayer script line, but no change. My
problem is that mplayer is not running in a shell where I can send it
signals or commands/keystrokes.

I have mplayer running in the foreground but it is nested in a
'while-loop'. The while-loop is backgrounded. This is done so mplayer
prevents the loop from playing multiple songs at once (which happens
when I bg mplayer and the loop continues, and the while-loop is
backgrounded to give control back to the UI while mplayer is playing.

So my problem is I don't have any control of mplayer or any way
(that I am aware of) to talk to it directly once the while-loop
detaches.

fyi, this is for a pico-ATX mini appliance I am building as a music
player for my living room. It uses a web interface to control mplayer,
volume etc. The playing script starts mplayer, then reprints the page
so the user gets status and control buttons. The control buttons send
diff 'post' data to the cgi script (usually the 'playing' script). I
use amixer for volume control and killall to skip tracks (kills mplayer
and the loop picks up at the next track). I am trying to implement a
pause/resume button. It works fine, except for the fast-forward
catch-up issue.

Thanks.
Pete