[mythtv-users] BBC HD (1080) h.264 / AVC playback

[Tim Small]

Hi all,

I've recently put together a new box, and thought I'd share my 
experiences viewing the BBC HD trials, which are broadcast in H.264 
(Mpeg-4 Part10 "Advanced Video Coding" AVC) as DVB-S broadcasts on Astra 
@ 28.2 degrees east.  The box uses a mobile Core 2 Duo T7400 (2.16GHz), 
on an Asus "N4L-VM DH" board (Intel 945 GM chipset, integrated "Intel 
GMA 950" graphics with an additional DVI "ADD-2" card - to provide a DVI 
output from the onboard graphics).  The box has 2 interleaved sticks of 
DDR-2 667, but I don't know if this chipset is capable of running them 
at the full 667 or not (I happened to have the RAM spare, and didn't buy 
it especially for this machine).

I used mplayer to play back recordings of "Planet Earth" in 1080p - 
1440x1080 16:9 25(?)fps - files which mythtv has recorded (but not 
transcoded).

I'm pretty sure that the transmissions are 1080p - I can't see any 
interlacing artefacts.

1. The i810 driver for the integrated graphics doesn't allocate enough 
resources for XVideo scaling at this resolution by default, and I ended 
up with the following entries in my /etc/X11/xorg.conf:

Section "Device"
        Identifier      "Intel Corporation Mobile 945GM/GMS/940GML 
Express Integrated Graphics Controller rev 3"
        Driver          "i810"
        Option          "Cachelines"    "1024"
        VideoRam        65536 # You don't actually need this much for 
1080p playback
EndSection


Although the Xorg i810 driver supports the XvMC (X-Video Motion 
Compensation) extension on the (ancient) i810/i815 integrated graphics, 
it doesn't appear to offer it on newer chipsets at this time :o(.  XvMC 
isn't any good for decoding H.264 anyway, but I don't know what 
facilities the GMA 950 offers which could assist H.264 decoding (other 
than de-interlace support), were the necessary hardware support implemented.

I am able to play back these recordings at full FPS, with the following 
mplayer options:

-vo xv -vfm ffmpeg -lavdopts skiploopfilter=all

One core is utilised at approx 90%, whilst the other remains largely 
idle (there is no multi-threading support in the H.264 ffmpeg decoder at 
present).

Without "skiploopfilter=all", the decoder can't keep up, but the drop in 
quality with the option in (at least on my 1280x1024 19" DVI monitor) 
seems negligible on this material.

I haven't tried getting mythtv to do the "skiploopfilter=all" option 
yet, as I'm not sure how to set that option, and haven't had time to 
look yet..

I did look into using the cheaper, and lower power (?), but also 64bit 
"Celeron M 520" on the same board (single "Core 2" core, 1M L2, 
1.66GHz), but it looks like this wouldn't have been fast enough for this 
material with the current software (this wasn't the only reason for 
choosing this CPU, as this box is not just intended for MythTV output!).

Attached is a screenshot from xosview whilst playing back the recording 
with mplayer.

Cheers,

Tim.


p.s. I'm using Debian "Etch" amd64, with mythtv and mplayer packages 
from Christian Marillat's Debian Multimedia repository.


p.p.s this box (with 2x 60G Toshiba 2.5" drives, a keyboard, a mouse, 
the stock Asus fan, and a bog-standard 330W ATX PSU) uses a fairly 
respectable (for the processing abilities, IMO) total of 64 watts as 
measured at the wall socket with both cores running 100% (running BOINC 
climateprediction.net), and 41 watts when sitting Idle at a logged-in 
KDE desktop (without any power saving).
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