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Discussion Starter · #1 ·
Starting with UVD2 and VP3, both, AMD/ATi and nVIDIA feature full bitstream support for all Blu-Ray video formats, including MPEG-2. Question is how can a decoder take advantage of that? DXVAChecker reveals what drivers provide to access the hardware decoders under Windows operating systems.



Figure 1 - DXVAChecker - HD4550 UVD2


In case of ATi, there seems to be no standard interface to offload the whole MPEG-2 bitstream decoding to the UVD. DXVA decoders still use the iDCT profile which is executed within shaders. Entropy decoding and motion compensation are handled by the CPU. Power consumption would come down quite a bit if all stages were decoded within ATi's UVD fixed function unit.


nVIDIA ION and all GPU's with >= VP3 on the other hand provide 'ModeMPEG2_VLD' to DXVA decoders, see figure 2.



Figure 2 - DXVAChecker - ION with VP3



From above figures, we can see, there are NO DxVA profiles support (on UVD compared to nVidia VP3) for:


1. ModeMPEG2_VLD | Yes, you didn't see wrong, the ATi cards don't support BSP for MPEG2 SD and HD contents.


2. ModeVC1_IDCT


3. ModeWMV9_IDCT


4. ModeH264_VLD_FGP


5. X8R8G8B8 FourCC.




Does anyone really noticed the above DxVA profiles limitations even in ATi's latest 5xxx series cards in your HTPC??
 

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Discussion Starter · #2 ·
No one really cares about the MPEG2 DxVA profiles support limitations on even the latest ATI 5xxx series UVD2?


I compared 13Mbps H.264 and 20Mbps MPEG2 and found latter has better video quality. Not saying the world best Japan BSD (24Mbps MPEG2) in video quality.
 

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Discussion Starter · #3 ·
I tried some high bitrates (18Mbps and above) MPEG2 HD channels here, some channels even got 20% CPU occupation on my 4 core Intel CPU (DVBViewer, CyberLink PDVD9 w/ DxVA)!! Compared with nVidia 8400's 3% CPU on the same MPEG2 HD channels, this was really unacceptable!!


So MPEG2 full DxVA support is essential. This is just the driver limitation, hope ATI video driver team can work to have full MPEG2 DxVA supports!
 

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The way I understand it, film grain is removed before compressing the movie which improves compressibility big time. This film grain is then compressed separately in an efficient way. If a decoder does not support FGT it can't reconstruct the film grain.


AFAIK no encoder takes advantage of that so far.
 

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Discussion Starter · #9 ·

Quote:
Originally Posted by CiNcH /forum/post/18144206


AFAIK 8600 doesn't feature full bitstream support for MPEG-2 either. This is only supported from VP3 onwards.

Sorry, it's a low profile nVidia 8400 suitable for HTPC years ago which was recommended by Tom's. Don't know if it uses VP3.
 

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Discussion Starter · #13 ·

Quote:
Originally Posted by kevinqian /forum/post/18158831


Lucky aussies and europeans get H264 content. ATSC is stuck in the 90s.


Mpeg2 decoding is really a nonissue as even an old P4 can do the job fine. What are you so concerned about?

Our satellite and cable HD channels are all in MPEG2 which have the bitrates of 18Mbps and above, so it's meaningful here to get full MPEG2 DxVA profiles support.
 

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Especially for high bitrate HD content, one will see quite a difference. It is not just about whether the CPU can handle it with ease or not. When using the DXVA iDCT profile for MPEG-2, the stages IQ, iDCT and MC are handled by shader and CPU ALU's, so even the stages that are supposed to be fully computed on the GPU by a dedicated processor are in fact only accelerated, so partially being offloaded to the shaders. A lot of calculations and also VLD to a full extent are computed by the CPU. Still both, shader and CPU ALU's, are general purpose nature, always requiring much more processing power to execute the same tasks compared to a dedicated hardware like the UVD.


When building a HTPC, one fights for every Watt to spare. Why not using the dedicated low power hardware if it is there but just lacking proper driver support?


Seems like VLD/bitstream-level decoding for MPEG-2 can be enabled via registry (see also DXVAChecker) for HD 4000 and 5000 series GPU's featuring UVD2 (key 'VForceUVDMPEG2VLD'). But it may not function correctly. So the way ATi deals with this issue is simply disabling the feature instead of debugging..
 

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Discussion Starter · #15 ·

Quote:
Originally Posted by CiNcH /forum/post/18159275


Seems like VLD/bitstream-level decoding for MPEG-2 can be enabled via registry (see also DXVAChecker) for HD 4000 and 5000 series GPU's featuring UVD2 (key 'VForceUVDMPEG2VLD'). But it may not function correctly.

Do you have an 4000 or 5000 card to test? How to check if the tweak works correctly or not?
 

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Quote:
Originally Posted by ter9999 /forum/post/18159877


Do you have an 4000 or 5000 card to test? How to check if the tweak works correctly or not?

I have a HD4550 and tested it yesterday (I read CiNcH's blog/comment on dvbviewer forum before).

I tested it with 10.1 & 10.2 drivers on Win7 x64.


After the Tweak DXVA-Checker showed me the ModeMPEG2_VLD profile but when playing back a file the system crashed with a blue screen.


When watching TV with DVBViewer, the system did not crash, but I only got sound and green picture.

Cyberlink properties showed that the codec uses a "BSP" profile.


When I deactivated ModeMPEG2_VLD, everything was fine,

Cyberlink properties showed an IDCT profile.



greetz,


sw4y
 

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Discussion Starter · #19 ·

Quote:
Originally Posted by sw4y /forum/post/18160275


I have a HD4550 and tested it yesterday (I read CiNcH's blog/comment on dvbviewer forum before).

I tested it with 10.1 & 10.2 drivers on Win7 x64.


After the Tweak DXVA-Checker showed me the ModeMPEG2_VLD profile but when playing back a file the system crashed with a blue screen.


When watching TV with DVBViewer, the system did not crash, but I only got sound and green picture.

Cyberlink properties showed that the codec uses a "BSP" profile.


When I deactivated ModeMPEG2_VLD, everything was fine,

Cyberlink properties showed an IDCT profile.

Thanks for your testing. This was indeed a horrible result! Don't know if 5000 series card gets the same result for MPEG2 DxVA2 BSP support.


Since there is an entry in registry, I think this is only the driver limitation. ATi should be blamed for the lacking of a BASIC function in their UVD.
 
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