[mythtvnz] Best way to reduce CPU use (by ~10%) during software encoding/decoding

[Aaron Whitehouse]

Hello,

I have just upgraded my HTPC (to one based on the AMD 780G chipset, as
mentioned in an earlier email). The weakest link in my new machine is
the CPU, which is a Sempron LE-1200 (instead of the 2.4GHz P4 in the old
machine). While I thought the Sempron would be faster, it seems to be
slightly slower at video encoding/decoding than the P4 was, meaning that
my current settings (512x576, 2200 bitrate, MPEG-4, quality between 2
and 15, max 3 quality difference between frames, scale bitrate for frame
size, HQ encoding and 4MV), which worked fine in Live TV (i.e. one
encoding stream, one decoding stream, no DCT encoding, no interlaced
motion estimation) on the P4, are slightly too demanding for the new
CPU. The new CPU is sitting at around 90+% in Top and is the video is
quite jerky. I am guessing that the CPU is hitting 100% on occasion,
stalling the playback.

I have two cards in the machine - a bttv software encoder and a
Hauppauge PVR-150 with MPEG-2 hardware encoding. I will probably switch
the default card to be the hardware encoder (MPEG-2 takes heaps of room,
but I have a new HDD), but I will still need to be able to record one
hardware, one software and play one back. Playing MPEG-2 actually seems
to take slightly more CPU than playing back MPEG-4, which surprised me.

So here is my question (after all of that background): I only think that
I need to reduce CPU use by about 10%, but I am not sure which settings
are the best to change in order to get that. Disabling 4MV or HQ
encoding saves a lot, but the picture isn't very good. Tweaking the max
and min quality makes some difference, but I'm not sure which to change.
What is the best thing for me to change?

Thanks in advance,

Aaron