Real CPU requirements for 1080p/i

[bitmonkey]

Ok, here's the deal - I don't have a totally unlimited budget, but want to future proof the MD I'm building and want it to play back the most complex scenes in x624 highest bitrate blu-ray rips flawlessly. The logic being that building it right this time is cheaper than building it twice.

I don't mind too much if there are small issues with 1080i, as I understand 1080i content is very rare and I could tolerate that being 99% perfect with tiny issues on very complex scenes, but 1080p must be absolutely 100% flawless at the highest bitrates and with the most complex scenes.

What CPU do I need?

I'm going to use a AN-M2HD board by the looks of it with 4GB of 800mhz RAM, content will be streamed over gigabit LAN (PXE booting the MD).

First I considered an AMD x2 5600+ as I'd heard it would do the job, but then I saw a page in the wiki mentioning issues with very complex scenes. I have now found the 7750 BE which is a phenom, 2.7ghz, apparently performance is on a par with the x2 6000+. Will this be adequate? I could overclock it a little if needed, but of course noise of cooling fans is an issue so would prefer not to. Will any of the AMD processors do flawless h624 1080p ? If I have to go to an Intel CPU that would suck, as I'd then have to find a mobo with everything I need (chiefly HDMI out and onboard nvidia).

thanks

[colinjones]

RAM will not have any real impact on this, and 4GB is overkill. 1-2GB is plenty. For CPU I would suggest the highest end CPU you can afford!! If it can do 1080p then 1080i isn't an isue as it is half the work!

But realistically, I would strongly suggest you focus on waiting for VDPAU support. Only then are you going to be able to guarantee 1080p H.264 high bit rate decoding with reliability. Then you can use a very cheap CPU, even an Atom, as all the work will be done by the GPU.

Now the GPU in the board you are talking about is an integrated 7050PV, which in theory should be capable of using the VDPAU extensions (generally only 8xxx/9xxx series chips support this, but integrated GPUs with PV, supposedly are supported as well). However, the cheapest option that will give you full support under VDPAU, plus very low power and small footprints are any of the nVidia ION boards coming out. The Acer Revo is a complete system and very cheap, and there are other mobo-only solutions being talked about on the forums right now.

VDPAU support is not in LMCE yet, but it will be and probably before 0810 goes to release.

[bitmonkey]

Hi Colin,

Thanks for the detailed reply.

The reason for 4GB is the box will be doing double duty and will sometimes be booted as XP for using photoshop which is the only thing I can't do with linux or bsd. My current windows box is becoming the core so I've finally kicked the windows habit.

You say 1080i is half the work - I must have misunderstood, because I was assuming that if there are say 25 frames per second, that 1080i must be 50 fields per second (each being half a frame) and that therefore there are twice as many fields to decode per second than using 1080p - where am I wrong here?

Thanks for the honest reply about decoding 1080p in software - I had been reading a lot of "it works but..." comments, then other people would say it was totally usable but to me totally usable means different things in different contexts - if I were watching video on my PC and there was an occasional skip or momentary slowdown I'd tolerate it, but if I brought say a dvd player and it did that I'd be returning it. Despite this being built around a PC it's basically intended as an appliance and should work as such - eg flawlessly.

I think given what you've said and that the box will be doing occasional xp/photoshop duties I'll go ahead and spec it as I was going to anyway as that will be a good usable spec for those purposes and should do acceptable 1080p for the time being whilst I wait for VDPAU.

I have read about VDPAU but found it difficult to get a clear idea how far away from usable it is - I will have to do some more googling. If you expect it out in 0810 then I guess it must be further along than I'd thought, can you give me some indication when 0810 is likely to be released? I haven't been able to find a schedule and presume linuxmce does not have set release dates.

[totallymaxed]

Ok, here's the deal - I don't have a totally unlimited budget, but want to future proof the MD I'm building and want it to play back the most complex scenes in x624 highest bitrate blu-ray rips flawlessly. The logic being that building it right this time is cheaper than building it twice.

I don't mind too much if there are small issues with 1080i, as I understand 1080i content is very rare and I could tolerate that being 99% perfect with tiny issues on very complex scenes, but 1080p must be absolutely 100% flawless at the highest bitrates and with the most complex scenes.

What CPU do I need?

I'm going to use a AN-M2HD board by the looks of it with 4GB of 800mhz RAM, content will be streamed over gigabit LAN (PXE booting the MD).

First I considered an AMD x2 5600+ as I'd heard it would do the job, but then I saw a page in the wiki mentioning issues with very complex scenes. I have now found the 7750 BE which is a phenom, 2.7ghz, apparently performance is on a par with the x2 6000+. Will this be adequate? I could overclock it a little if needed, but of course noise of cooling fans is an issue so would prefer not to. Will any of the AMD processors do flawless h624 1080p ? If I have to go to an Intel CPU that would suck, as I'd then have to find a mobo with everything I need (chiefly HDMI out and onboard nvidia).

thanks

I would suggest that you look at this differently...as Colin has already suggested... even with a big hot processor (choose either mainstream brand) you will find that an nVidia MD will struggle to playback 1080p/h.264 high-bit rate encoded video. However help is on the way for nVidia based MD's in the shape of the new vdpau support in current nVidia drivers. Vdpau offloads most of the heavy-lifting for playback of h.264 content to the nVidia GPU. See this Youtube clip of the ATOM based nVidia Ion demonstrator running XBMC at 1080p and playing HD content;

http://www.youtube.com/watch?v=rv1Q_DWieAQ

The above clip amply demonstrates what the ATOM/Ion combo can deliver :-)

...and of course now we have inexpensive motherboards and pre-built machines using the ATOM/Ion. The last part is the software support in LinuxMCE to take advantage of it... and several of us are working on fixing that.

All the best

Andrew

[colinjones]

You say 1080i is half the work - I must have misunderstood, because I was assuming that if there are say 25 frames per second, that 1080i must be 50 fields per second (each being half a frame) and that therefore there are twice as many fields to decode per second than using 1080p - where am I wrong here?

Precisely the opposite. With 'p' there are 50 frames per second, each 1920x1080. With 'i' there are 50 fields per second (assembling to make 25 frames per second), each 1920x540... ie the same number of fields/frames per second, but 'i' has half the vertical resolution because only alternate lines are scanned.