Real time video

General "chat", not necessarily MTX related
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Martin A
Posts: 417
Joined: 09 Nov 2013 21:03

Real time video

Post by Martin A » 07 Aug 2015 11:51

1024MAK wrote:So does that mean I won't be able to connect up and use my 4T byte HDD with a certain film (featuring a lovely woman and an MTX) and play the movie on my lovely MTX? :cry:

Mark's message got me thinking, IS it possible to do movie playback on the MTX at say 25fps.

Full screen colour is a non starter, the VDP doesn't have the colour resolution.

Full screen mono, in graphics 2, that's 6k of data to shift through the VDP ports for each screen. The fastest the VDP can take the data is 32 Z80 cycles per byte. 6144 x 25 x 32 is 4915200, almost 25% too much.

For a quarter screen, in mono is the answer maybe?

Wide screen Video uses a ratio of 16:10, so a display 128 pixels wide would be 80 pixels high. that's 160 characters cells. So Graphics 1 could be used instead of graphic 2, saving the complications of managing the separate 2k vram blocks in G2.

160 characters is 1280 bytes, making the transfer time 1280 x 25 x 32, a much more manageable 1024000 cycles

The raw read speed of the CFX's is IDE implementation is currently 85 cycles per 2 byte word.

The 32,000 bytes a second required would need 1360000 cycles on the CFX.

So, a 1/4 screen mono display at 25fps is possible, 60% of the CPU time is taken up with reading the data off the drive and transferring it to VRAM, the remaining 40% would have to cover all the processing overheads (and audio??)

"The Movie" would have to have been converted to the 128x80 mono format prior to playback of course!

Wiki says its 94 minutes, so 94 x 60 x 32,000 = 180 480 000 bytes. That's within the limits of the current LBA implementation on the CFX board as that uses 24 bits and can address 8 gig.

Anyone want to volunteer to do the conversion ?

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