[mythtv-users] Dropped frames, simultaneous recordings and process priorities.

[Frank Feuerbacher]

Our box is a 4 CPU 3.4GHz i5, 8G ram, Ubuntu 12.10, with a PCIe InfiniTV 
4-tuner card (which produces mpeg-ts content). It usually has XBMC 
running idle on it and mythtv. We also do background Handbrake encodings 
and editing with Avidemux (as needed). I notice that under some 
circumstances, our recordings have considerable noise, especially during 
the first few minutes. My theory is that this occurs when consecutive 
movies are recorded, or perhaps when more than one is recorded at once. 
I do have the default set to record 1 minute before and after a show, so 
we could be using two tuners and double the I/O for a minute for 
consecutive recordings. On some occasions we might record two 
consecutive shows on two channels simultaneously, so I guess we could 
briefly have 4 recordings at once.

After a recording is complete, I make a copy of the .mpg to the same 
disk to simplify the task of my wife copying the file to her machine for 
Avidemux (avoids symlink issues). I also create an Avidemux index file.

I see that mythbackend runs with a normal *nice* value and with *ionice 
idle*. I just modified my post-record script to run the copy and 
avidemux create index with ionice idle and nice 10. Perhaps this will 
solve my problem. But I am curious why mythbackend doesn't run with a 
normal *ionice* value. Is the content from the InfiniTV considered I/O 
by ionice and impacted by it? Does mythtv buffer frames as needed when 
the I/O is backed up a bit?

If I have to I'll rearrange the disks or acquire more or faster (SSD) 
disks. But I'm not sure if *ionice**idle* requires ALL I/O to be idle, 
or if it is on a per-device basis. Today I have a disk for the normal 
Ubuntu stuff (root, /usr, /home, /tmp). I have one, /pvr, for mthtv and 
a staging area for movies to be edited or encoded and one for movies 
after they have been encoded for XBMC. They are not fast disks (5400)