> Does any loseless compression algorithm require the entire set of data for
> read access before it begins compression? If you wanted to encode audio with
> a loseless compression, could you do it in real-time or would you need to
> wait until the entire recording is complete, and then compress afterwards?
> Would the results be as good in real-time than as a post-process?
I'm sure that there are some algorithms that require access to the entire
data set before they could compress it. I can't name any off the top of
my head though.
Compress, gzip, and bzip2 (all from the Unix world, although Windows
implementations exist) are able to compress a stream of data in real time
(this is actually their normal way of handling things). These all use
lossless compression algorithms with varying degrees of speed and
compression.
One advantage of a non-realtime compression algorithm is that it can be
much more complex than a realtime one. If a realtime algorithm is too
complex it won't be able to keep up with the input data and will lose
data. This isn't an issue with non-realtime compression since it doesn't
have to keep up with an input, it can work through at its leisure.
As for quality of the results, that's dependant on the specific algorithms
in question.
> > This is, coincidentally, why audio MD equipment would be very poor for
> > data storage. I believe this has been discussed on-list a few times.
>
> ...and if I understand correctly, data would have to be encoded into some
> sort of audio stream designed to be completely loseless when converted with
> ATRAC, right? ...or maybe embed some sort of error-correction mechanism...?
As I said, these have been hashed out on the list before. The gist of it
all seemed to be that you would fit a very small amount of data onto a
disc, it would take a long time (74 minutes for a full disc) to read and
write the data.
This isn't to say that it can't be done, just that it would be fairly
impractical when compared to using something designed for storing data.
-- Dave Kimmel
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ICQ: 5615049
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