[MPlayer-users] SIGCONT causes fast-forward effect

[Oliver Seitz]

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