[opendtv] Re: QuickTime 7 HD Gallery

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sun, 1 May 2005 09:42:34 -0400

At 9:51 PM +0200 4/30/05, Donald Koeleman wrote:
>Does this only work on Apple computers?
>Is the codec also available for the pc, the site only mentions Tiger?
>If it is fully AVC compliant it should also be viewable on alternatives
>like: http://www.mainconcept.com/h264_encoder.shtml.
>Any other interesting encoder/decoder alternatives out there for the pc,
>preferably free ones?

Only Macs running Tiger and QuickTime 7.

720P playback is within reach of affordable Macs like the Mini and 
iMac. This will be the main thrust for Apple, as there are multiple 
roadblocks to playing 1080P on any affordable computing platform 

Here are some of the issues, and why it may take a bit longer to 
release QuickTime7 for the PC.

1. Decoding bandwidth - this is processor intensive and is typically 
split between multiple processors, including graphics co-processors 
on the video board.  With previous incarnations of MPEG some of the 
routines werre handed off to the graphics co-processors, which had 
loops to hadle things like the DCT transform. But H-264 does not use 
the DCT transform. Apple uses the Alti-vec co-processors in the 
PowerPC chips to accelerate some of the sub routines. Alti-Vec does 
not exist n PCs, but there are other co-processors in the Intel and 
clone chips that can be used - but this requires additional code for 
those platforms.

2. Bus bandwidth - moving 2 mpixels to the graphics board at 60P or 
able takes a lot of bus bandwidth - more than most current machines 
can support.

3. DVI Bandwidth - moving 1080@60P or above to a high resolution 
display requires a very fast viceo card. Apple requires a board with 
dual DVI for the 30 inch Cinema display (2560 x 1600), and recommends 
a 128 MB graphic card for the 23 inch display (1920 x 1200), if you 
want to play 1080P full screen. Apple controls the graphics cards 
they support in the Mac - there is much more variability on the PC 
side, which complicates HD play out.

By the way, I spoke with a friend at Microsoft who indicated that 
they will support H.264 play only in a future Windows Media release. 
My guess is that this will NOT extend up through the HD level, but 
rather will be focused on lower resolution/bitrate applications.

And for the record, Apple demonstrated 1080@24P H.264 playout during 
NAB (I believe that the actual screen refresh is 60P).

For both Apple and Microsoft, the sweet-spot for HD playout will be 720P.

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