[mythtv-users] Mythmusic buffer underflow with audio cds

Paul Sands usg990a at cebridge.net
Sat Nov 14 02:31:42 UTC 2009

Frank Ahrens wrote:
> Hi,
> i have got a problem which i can't find solved in all discussions
> available through google.
> All my mythtv usage is nearly perfect. The only item i can't solve, ist
> playing music directly from cd with mythmusic.
> 1.) the drive led lights up (drive access)
> 2.) the sound stutters
> 3.) drive access stops
> 4.) sound will be perfect for ~10sec and
> 5.) back to 1)
> In my mythbackend.log i can see  many buffer underruns.
> The sound is ok with other players such as xine or kscd.
> In this cases the drive led is nearly on all the time or in much shorter
> times.
> I have got the problem on my mythbuntu systems (8.10 with MythTV 0.21
> and 9.10 with MythTV 0.22) on my HTPC
> and on my Notebook with OpenSUSE 11.1 with MythTV 0.21.
> It seems, that mythmusic first sucks all data out of the buffer before
> reading new data from drive.
> I think many user must have this problem, because it's on all my
> installations.
> Could someone help me to solve it?
> Many thanks in advance.
> Frank

This sounds similar to some of the issues encountered with DVD playback
through the internal player. The solution I found was to use hdparm to
manual set the readahead (buffer) to 2MB for playback

hdparm -a 2048/ //dev//path/to/your/cd-drive/

This will create software buffer of 2MB that works independent of any
program. I know mplayer (and I suspect xine) uses a built-in buffer
above the hardware buffer of the device to ensure smooth playback.

As for a permanent fix, a ticket would likely need to be opened.


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