transcoding video for freerunner 240x320 mode

[EdorFaus]

On 07/02/2012 10:24 AM, Christ van Willegen wrote:
> On Mon, Jul 2, 2012 at 7:17 AM, robin<spielraum at web.de>  wrote:
>> but still why can it run a 240x320 scaled to 480x640 but not a native 48x640?
>
> Because the graphic chip does support stretching 240x320 to 480x640
> natively, but does not have enough horsepower to drive all pixels
> individually.

If I remember correctly, the main issue is the bus bandwidth - the bus 
is simply too slow to shuffle bits from main memory to the chip fast 
enough to do 480x640 video with a decent frame rate, and this is a 
hardware limitation, so not really fixable in software.

240x320 on the other hand, is only a quarter as many pixels, meaning a 
quarter of the bits, so only a quarter of the bus bandwidth is required 
- and this is within the hardware limitations.

(As for why this limitation exists, well, I seem to recall hearing that 
the makers of the graphics chip were impressed we had gotten as much out 
of it as we had, as it was not really intended to do much at all in 
480x640 in the first place.)

-Frode