Movie-JPEG

John.Maloney at disney.com John.Maloney at disney.com
Thu Nov 29 04:38:18 UTC 2001


At 9:36 PM -0800 11/27/01, Avi Bryant wrote:
>I don't imagine this'll build on the mac, but
>http://sourceforge.net/projects/dv2jpg/ will convert directly from DV
>files into MJPEG - so if MJPEG support is indeed added this might be a
>useful addition.  More links are at http://mjpeg.sourceforge.net.

Thanks for the links. MJPEG might, indeed, but useful. It also looks as
like, on Macs at least, Quicktime Pro can do a lot of useful conversions,
and it only costs $29. Sorry, I don't know if QT Pro is available for Windows
or its price.


Re:
>Out of curiosity - framerates have been mentioned, but not resolutions.
>How large a file can the JPEG plugin decode in 1/30 s?

That depends on the processor/bus/cache speeds, of course. I get around
55-65 fps playing a 320x240 movie on a 500 MHz G4 Titanium Powerbook.
That includes reading from disk and displaying the decoded output, as
well as playing sound. Decode time is proportional to area, so one should
be about to decode an image about sqrt(2) larger than that in 1/30th second
in the context of playing a movie, or a bit bigger if you didn't display the result.

There is also some speed difference based on the quality factor used to encode
the move. Higher Q frames take a little longer to decode. In my experiments,
the difference was no more than 10%, but I didn't compare the very extreme
ends of the scale.

The movie player can also scale up its output using WarpBlt (at some additional
cost, of course). I'd probably encode movies no larger than 480x360 with the
idea that this could be scaled up if a larger playback is desired, but it would play
at a full 30 fps on a high-end machine. Assuming the movie still looks good
at 15 fps, this movie would playback reasonably well, skipping every other
frame, on a machine half as fast as my hotrod.

But these are just some rough guidelines; please feel free to do some benchmarks
of your own. (Note: The "testPlay" method in JPEGMovieFile displays all
the frames of a movie at full speed and answers the frame rate achieved.)

	-- John






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