Re: Ogg encapsulation

On Sun, 4 Apr 2004, Glenn Randers-Pehrson wrote:

> At 11:23 PM 4/3/2004 -0800, Ralph Giles wrote:
> >Speaking of, I have an innocent question. Is there any way to write
> >uncompressed IDAT chunks? If not, what's the fastest mode of encoding
> >png data? There's a niche for a lossless video file format, and Ogg MNG
> >+ FLAC (our lossless audio codec) seems like it could fit the bill. I do
> >understand that zlib is very fast on modern 2 GHz machines, but in live
> >recording it's nice to be able to minimize overhead if necessary.
>
> I think zlib level 0 compression is uncompressed.
> The HUFFMAN_ONLY compression strategy is also very fast.

If you are using zlib-1.2.1, try Z_RLE. It is about +5% slower than
Z_HUFFMAN_ONLY, but it gives a little better compression.

If you use any of these two strategies, chances are that you might
actually save time, compared to the uncompressed solution. This is
because the processing overhead of Z_RLE & friend might be smaller than
the I/O overhead incurred over the larger amount of uncompressed data.

Also, if the images are continuous-tone, try using the fixed delta
filter "sub" or "up" (fast), or the adaptive delta filter (better, but
slighly slower).

Best regards,
Cosmin

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