
   Atari STE  high-color AV playback at 25 fps

Features: 
Resolution 320x160 px.
Frame rate: 25 fps
Audio:  mono, 25033 Hz sample rate
Max length - limited only by storage capacity

Early development. This uses Douglas Little's Photochrome conversion and displaying SW/code.
Mode is single field, 4096 c.  PCS format, 320x160 lines. It is choosen because is good for usual 16:9 AR sources, and leaves more time for data load.

This demo is playable well only with emulators - Steem or Hatari, with GEMDOS type
hard disk emulation. It is because high data transfer rate from disk required. On real STE
HW it will not work well, and reason is insufficient speed of disk transfers + additional slowness caused by FAT16 filesystem.
Try on Steem with Pasti emulated hard disk - it will be too slow, even if it has much higher raw disk transfer than any Atari hard disk IF. 

So, what is the point, if this can not work on real Atari HW ?
Actually, it can, but only with mine cartridge port IDE adapter, which can over 2.5 MB/sec.
And only if small mod in STE is done. As that adapter is not yet available, no point to publish version for real STE at moment. Yes - real STE needs different version - where displaying code is same, but loading of data must be performed with raw disk access, because, as said FAT16/AHDI is not good enough for this.


Technical background:  Single field PCS pic. (screen) takes about 50 KB. Displaying it on STE takes about 63 % of CPU time. So, not much left for other things, like disk access. DMA ? Unfortunately it can not be used, because it will destroy timing of hi-color displaying. 
Little calculation says that for contigous playback at 25 fps we need about 1250KB/sec transfer. It is possible with better hard drives and interfaces. But not for hi-color playback, because we can do load only in non-scanline periods, so max about 35% of time. 
If we reduce screen size, to 160 lines, it will give about 48% of time for load. And needs of course less transfer too - about 1050 KB/sec.  Still too much for available solutions.
But my CATA with superfast movem transfer mode can over 2.5 MB/sec, so can do 1050 in 48% time. But, as said only in raw mode. So, playback SW for real STE must perform low level sector readings in non-scanline periods. AV data most be saved on disk to specific location, and not by filename.

Future plans:  320x200 px. at 25 fps, and more colors. With updating colors directly from hard disk, we can transfer part of data during scanlines + having more colors per line. But it needs new PCS or other type of high-color format. I'm in contact with Douglas Little and Cyg, so likely, they'l make some support for it.  
And even using of current formats is possible with special code (where update colors directly from drive). 




Abort playback with Esc. key.

 PP, Oct. 2012
