[Ti] Re: MPEG, was "Re: Dual Layer cable for Powerbook G4 400"

[Kynan Shook]

Actually, as far as I'm aware, most recent video cards have built-in  
MPEG-2 decoding support, which OS X's DVD player is using.  They are  
designed specifically for DVDs, and access to the video card is  
difficult, so any MPEG-2 decoding other than a DVD is done in  
software.  Some video cards also include MPEG-2 encoding, or MPEG-4  
acceleration.  A GPU is not a second CPU that's just dedicated to  
graphics; it has lots of specialized features that are only useful  
for special-purpose graphics operations.  That's why the video card  
in my G5 has about 220 million transistors, when each of the G5  
processors only has about 58 million.

So, DVD MPEG-2 is all hardware (plus a bunch of CPU overhead).   
Everything else (Apple's MPEG-2 playback component for  Quicktime,  
for example) is software, as you noted.

EyeTV also uses MPEG-2; I have an EyeTV 500 for receiving HDTV.  It  
will run on my PowerBook G4 17"/1 GHz, but only at about half the  
normal frame rate.  Elgato says that a 500 MHz G4 or better is  
required for HD MPEG-2 decoding, and a dual-processor G5 is required  
for full frame rate, full resolution HDTV.  Of course, DVDs are lower  
resolution than HDTV, but even my 500 MHz Ti never struggled on a  
DVD; hence, evidence that the DVD is using hardware acceleration.

I'd bet that the video card in your DVR contains MPEG-2 decoding, and  
that the PowerPC 750 is at 90% just from all the overhead of moving  
the data around and such.

Chris Olson <chris.olson at astcomm.net> writes:
> On Dec 14, 2005, at 9:56 AM, Mikael Byström wrote:
>
>> Doesn't the graphic cards of the titaniums do MPEG-2 decoding? At
>> least earlier models of iBooks and the Pismo had this built in by
>> default hardware.
>
> There's no way.  The GPU simply doesn't have enough processing power
> to decode MPEG-2 on the fly.  For instance, a real hardware MPEG-2
> decoder such as that found in my DVR cable set-top box has a
> PowerPC750 (no AltiVec support) processor running at 700 Mhz.  And it
> runs at 90% load decoding a HDTV MPEG-2 stream.
>
>> However, at some list I was reading none of us could determine for
>> sure whether Apples software was actually making use of said
>> builtin decoders. If not, the DVD player apps sure decodes MPEG-2
>> much faster than VLC or MPlayer. I think the latter 2 do it
>> completely in software?
>
> They all do it in software.
> ...