Re: a subtitle format

Hi there

--- Christian HJ Wiesner <[email protected]> wrote:
> 
> Liisachan, thanks for the input. Am i correct the
> .SUB file contains 
> simple Bitmap images for every subtitle ? In this
> case the
> 
> 'S_IMAGE/BMP'
> 
> codec ID could be used, and the .IDX file could
> simply be translated 
> into matroska's block time codes, so it would
> disappear completely. 
> Probably the easiest and best way to mux .SUB
> subtitles into matroska, 
> and we had hardware support for this also once i
> manage to convince KiSS 
> or Neuston to support matroska in their standalones
> ...
> 
> @Gabest : was it possible to include libpng into
> VobSub, such that the 
> Bitmaps could be compressed to PNG, without altering
> anything ? Of 
> course, matroska codec ID would then be set to
> 
> 'S_IMAGE/PNG'
> 
> but the timing information ( .IDX file ) was exactly
> the same.
> 

Before starting to do this (using PNG images instead
of BMP ones for subtitles) someone should do a test to
see if this wouldn't be a problem for realtime
playback.
To let you know, in VirtualDubMod I can only reach
45-50fps by _only_ decompressing PNG files to BMP
24bits (and _without_ showing them, just decompress
them in memory). Doing the same thing with the
original DivX5 compressed video clip I reach 90fps !!!
And yet the size of the image is 576x400, and I have a
XP 2400+.
Of course in subtitles you only need to decode an
image once in a while (i.e. when a subtitle begins)
but what I mean is that deocmpressing a PNG image take
some time (and of course some CPU power), even more
than decompressing the same image compressed with
DivX/XviD. If decompressing the image takes too much
resources and make the clip freeze a bit (even only
for one frame) this is already too much and will be be
highly noticeable during playback.

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