[mythtvnz] CPU required for Freeview HD

[Steven Ellis]

On 20/08/2008, at 4:45 PM, Robin Gilks wrote:

>> The H264 decode flatlines all OSs if done in software due to the
>> complexity of the decode when dealing with our broadcast streams.
>>
>> I've compared Linux and Mac software decode on the same hardware,
>> EyeTV vs MPlayer, and they appear to use similar amounts of CPU.
>>
>> The best windows codec for software decode is CoreAVC which is a
>> proprietary commercial codec.
>>
>> Until we get a way to accelerate some of the decode on the GPU we are
>> going to lag behind Windows users who have hardware accelerated  
>> decode
>> via the main graphics card vendors.
>>
>> As to STBs, as mentioned they have chips designed to accelerate the
>> decode in hardware. If you have had a play with the Zinwell STB you
>> would notice that it can get very hot due to the load.
>>
>> Steve
>
> So if all the work is done in the CPU, would a mother board such as  
> the
> "Asus M2A-VM HDMI Motherboard" with an ATI embedded video controller  
> do
> the job or is it still better to spend another $40 or so and use an  
> nvidia
> based board such as the "Asus M3A78-EMH HDMI Motherboard".


The pay off with the GPU will come in with the new Google Summer of  
Code projects to perform GPU based acceleration.

>
> c
> In either case, what would be the minimum spec CPU required (assuming
> these m/b will support the required speed that is!!) to handle both  
> TV1
> and TV3 HD?
>

I did a bunch of performance comparison tests on an X2 3600+ test rig  
today. I looked at the CPU load for both H.264 and MPEG 2 playback of  
the same channels, and locked the CPU to its max frequency of 2GHz.

I also used the CPU++ profile and allocated a max of 2 cores to video  
decode. It appears that some of the frames are slice compatible so  
there is a benefit in enabling dual CPU, but until FFMPEG can do true  
multi cpu decode we really need a CPU fast enough to decode on a  
single core. This is a shame given the drop in price of triple and  
quad core processors


Channel                 	  Resolution	Load H.264	Load MPEG2
freeview|HD  	           720p	       95-100+
TV One                          	720p		98-108		11-15
TV 2				720p		100+		11-15
TV 3				1080i		130+		12-15
C4					576i		45			13-15
TVNZ 6				576i		26-35		9-10
Sports Extra			576i		25-40		10-12
Maori				576i		37-40		9-10

Now the CPU load for C4 on freeview|HD is a little higher than the  
other channels, which might be explained by the higher bit rate they  
are using compared with TVNZ 6+7 etc.

For SD it appears we need 3.5 - 4x the CPU of SD and the X2 3600+ copes

For 720p the CPU is borderline and occasionally copes.

For 1080i I'm well out of power.

Right now I'd look at the fastest 65W processor I can buy. Sadly the  
only X2 5600s in the market are still 89W units, so it would be a 5400  
which runs a 2.8 GHz. The question is will this be enough?


In the Intel space I've been playing with a MacBook and EyeTV on a 2.4  
GHz T8300. Eye TV runs both cores at 90% when running TV3. I need to  
do a reboot and try mplayer native under Ubuntu to see how it compares.

Steve


Steven Ellis - Technical Director
OpenMedia Limited
email   - steven at openmedia.co.nz
website - http://www.openmedia.co.nz

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