[Matroska-devel] Re: Re: EBML (subitles)

Martin Nilsson nilsson at pike.ida.liu.se
Wed Mar 10 22:30:13 CET 2004

unmei wrote:

> i'm currently developing a new graphical subtitle format. It's in the 
> early implementation and still change phase but it shows good results so 
> far. I hope it will allow to compress full color subtitles at about the 
> size of (4 color) sub/idx. I think 1 mb per stream (language) is 
> possible and maybe even 400 or less kb could be attained. I designed it 
> to be not CPU demanding by not incoprorating sophisticated compression 
> schemes (_not_ like png, lzw et all) but my current encoder is extremely 
> slow (probably because i re-resize the target array quite often and 
> hopefully more avoidable stupidities).

As I've already mentioned I don't think that the "sophisticated 
compression schemes" you mention is a problem. It is usually quite cheap 
to decompress them. It is often the predictors that are time consuming. 
To counter a measurement made in another post, I tried to see how much 
PNG data I could decode while playing an ordinary TV-rip avi. On a 1GHz 
PIII I could decode 20 1000x1000 pixels PNG images per second without 
losing framerate in The West Wing. And subtitles rarely change once 
every frame nor is 1000x1000 pixels. I didn't use libpng though.... Note 
that alpha blending isn't a concern since all modern graphics cards can 
do it in hardware.

Do take in consideration that for many applications it is beneficial to 
have the textual data alongside the rendered data, to. e.g. facilitate 
text search.

/Martin Nilsson

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