The most demanding task for a high-definition HTPC is playing (i.e. decoding) H.264 encoded movies. H.264 contents playback experience depends on:
CPU processing power
GPU assist on the decode process
Playback software and the video card driver
So necessary CPU processing power and hence your CPU choice heavily depend on the video card you use.
For a pure playback machine with a NVIDIA GeForce 8600/8500 or ATI Radeon HD 2600/2400 video card:
The GeForce 8600/8500 and Radeon HD 2600/2400 GPUs are equipped with H.264 decode process engines that 100% offload H.264 decode work from the CPU. With these GPUs, any machine with a decent CPU (single-core or dual-core) can play even the most demanding H.264 contents pretty easily. Moreover Radeon HD 2600/2400 GPUs also 100% offload VC-1 decode work. Please read the two articles HARDSPELL.COM – DX10 is universalizing: G86/G84 complete test! (April 18, 2007) and HARDSPELL.COM – Face to DX10 and HD times! HD2000 rounded test (May 21, 2007) to see how effectively these GPUs decode H.264/VC-1 encoded HD contents.
Picks
AMD Athlon 64 X2 3600+ ADO3600DDBOX (Brisbane core)
Specs: Socket AM2, dual-core, 1.90GHz, multiplier x9.5, 2 x 512MB L2 cache
Price: $69
Notes: Right now this is the best bang for your buck. You don't need to overclock it for playing back HD contents smoothly. Of course the chip can overclock to as high as 3.1 GHz (60% increase) if you are lucky.
In case you use a GeForce 7x00/8800 card or an ATI Radeon X1xxx video card or an IGP, and/or you want to do CPU intensive tasks such as encoding quickly:
The GeForce 7x00/8800 or ATI Radeon X1xxx GPUs or the currently available IGPs offload the decode process for HD contents only partially and therefore you need a powerful CPU. The AnandTech article HD Video Playback: H.264 Blu-ray on the PC is a good source on this matter (though it is slightly dated). For such a system Intel Core 2 Duo processor is best suited (at least until the release of the AMD K10 processor).
Picks
Intel Pentium E2160 (Allendale core), to be released in June 2007.
Specs: 1.80GHz, FSB 800MT/s, multiplier x9, 1MB L2 Cache, No support for VT
Price: $84
Notes: This dual-core processor is based on the same Core microarchitecture as the Core 2 Duo processors. 1.80GHz is not enough to play back HD contents smoothly and you will need overclock it. To achieve the same frequency as E6600, just set the motherboard's FSB to 266MHz (266MHz x 9 = 2.40GHz). It can be overclocked easily to 3.0GHz = 333MHz x 9 with the default CPU voltage. However not every motherboard supports E2160 (actually the FSB 800MHz processors in general) properly. In many cheap motherboards FSB cannot be raised past 265MHz (so E2160 runs only at 2.39GHz = 265MHz x 9, that's not bad at all though). ASUS P5B series and GIGABYTE GA-965P-S3/DS3 work with E2160 most easily. If you are unfamiliar with overclocking, please see Reference: Overclocking Guides – Intel.
Intel Core 2 Duo E4300 (Allendale core)
Specs: 1.80GHz, FSB 800MT/s, multiplier x9, 2MB L2 Cache, No support for VT
Price: $113
Notes: 1.80GHz is not enough to play back HD contents smoothly and the same comment as E2160 applies to E4300.
Intel Core 2 Duo E6600 (Conroe core)
Specs: 2.40GHz, FSB 1066MT/s, multiplier x9, 4MB L2 Cache
Price: $224
Notes: If you need the support for Virtualization Technology (seldom used in the desktop environment) or if you want 4MB L2 cache or if you chose a motherboard that cannot be overclocked or if you don't want to be bothered with overclocking at all, this is it. E6420 (2.13GHz, $183) is a slightly cheaper alternative.
AMD Athlon 64 X2 4800+ ADO4800DDBOX (Brisbane core) (or above)
Specs: Socket AM2, 2.50GHz, multiplier x12.5, 2 x 512MB L2 Cache
Price: $129
Notes: This is the perfect CPU for the AMD platform.
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Low-End System
The following system has enough power to play back every kind of HD contents smoothly without overclocking. The processor can be overclocked very well if necessary.
Processor: AMD Athlon 64 X2 3600+ ADO3600DDBOX 1.9GHz Socket AM2. $69
Motherboard: GIGABYTE GA-M61P-S3 GeForce 6100/nForce 430 ATX. $73
Video Card: GIGABYTE GeForce 8500 GT GV-NX85T256H. $98
Memory: Corsair Value Select PC2-5300 2GB VS2GBKIT667D2. $65
Hard Drive: Samsung SpinPoint P120 250GB SATA SP2504C. $63
Power Supply: Antec EarthWatts EA 380. $41
Coaxial S/PDIF Bracket. $7 (DIY; Please read the section "About S/PDIF")
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The most important criteria for choosing a video card for HTPC are:
Hardware assist for decoding HD contents (of all three formats MPEG-2, H.264, and VC-1)
HDCP (High-bandwidth Digital Content Protection) support
Picture quality
How about HDMI? HDMI (High-Definition Multimedia Interface) is an high-definition digital audio/video interface that is replacing analog audio/video and older digital standards such as DVI and has become the de facto standard interface in the consumer electronics market. HDMI 1.0/1.1/1.2 provides 4.9 Gb/s bandwidth and the current HDMI 1.3 provides 10.2 Gb/s that has enough headroom for 1080p at 60Hz and 8 channel/24 bits/192 kHz LPCM audio (e.g. sounds decoded from the new digital audio codecs Dolby TrueHD and DTS-HD Master Audio) as the following simple calculation shows:
1920 x 1080 pixels x 60 Hz / 0.95 (5% overhead) = 131 MHz (megapixel/s), 131 MHz x 24 bits = 3.14 Gb/s
24 bits x 192 kHz x 8 channel = 36.9 Mb/s
HDMI video is compatible with the existing digital standard DVI and in fact one form can be converted to the other via a simple adapter. So there is nothing new. In contrast HDMI audio completely takes over the aged digital standard S/PDIF which supports only stereo PCM and 5.1 Dolby Digital/DTS with the maximum bandwidth around 12 Mb/s.
Unfortunately HDMI audio has not been realized yet in the PC world and we are still confined to S/PDIF. As a matter of facts, every HDMI video card simply passes S/PDIF signals from a sound card or onboard audio codec over the HDMI connector. Thus there is no real advantage of the current HDMI solution over the existing DVI + S/PDIF solution. Recent IGPs (ATI Radeon Xpress 1250 for Intel and AMD 690G) are no exception. Right now the only way to take the full-rate lossless multichannel sounds from the PC is use analog outputs.
NVIDIA Video Cards with the Second Generation PureVideo HD Engine
NVIDIA's second generation PureVideo HD engine provides 100% offload for H.264 decoding. That means that any decent PC with a video card with this engine can play back HD contents smoothly. The new engine consists of
VP2 (the new Video Processor)
H.264 BSP (Bitstream Processor)
AES-128 Decryption Engine (AES = Advanced Encryption Standard)
The first two engines accelerate the four major steps of the decode process for MPEG-2, VC-1, and H.264:
bitstream processing (reverse entropy) (by H.264 BSP; only for H.264)
inverse transform (by VP2)
motion compensation (by VP2)
deblocking (by VP2)
and the AES-128 Decryption engine accelerates the decode of the AES-128 encryption protocol. Among them offloading the bitstream process in the H.264 decode process dramatically reduces the CPU usage.
However there is no big difference in the CPU usage in decoding VC-1 between the original PureVideo HD engine and the reworked PureVideo HD engine as the bitstream processor is not for VC-1.
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Так что давайте не будем путать сюда свои HD рипы.