[Matroska-devel] Request for a hi-speed bitmap compression format standard

Christian HJ Wiesner chris at matroska.org
Mon Aug 11 14:10:58 CEST 2003


Christian HJ Wiesner wrote:

> PNG was our first bet ( of course ), but unfortunately the results 
> were proving that its unusable for our purpose, at least in its 
> current form, as the necessary CPU power to decode a PNG compressed 
> subtitle bitmap is simply too high. Imaging that we will play the 
> movies on normal PCs ( min standard should be a PIII 800 MHz as per 
> our recommendation ), and the CPU has to
>
> - decode the video, mainly MPEG4 or RealVideo9 ( very CPU intensive, 
> especially for higher resolutions )
> - decode the audio, very often 5.1 AC3 or 5.1 AAC tracks
> - decode the compressed subtitle bitmap 


Something weird came to my mind, and for very good reason i won't copy 
the PNG and MNG lists on this email :

What do you think, how big would a MPEG1 compressed picture subtitle be 
? MPEG1 has P/B frames already, so for a typical 720 x 574 ( numbers by 
Gabest ) *DECODED*  RLE VOBSUB bitmap with 4 bits per pixel ( 16 colours 
in the main palette, 4 colours selected for every subpicture, equals 2 
bits per pixel, but when decoded the bitmap can be shown as 4 bits per 
pixel in full resolution ).  MPEG normally performs pretty well on 
single coloured ( black ) backgrounds already, and we could maybe bring 
the overhead down significantly by using lacing ?

MPEG1 encoding is free, and MPEG1 decoding is fast

Crazy idea ?

Christian




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