Hi,
there should be only one compression algorithm. Otherwise a reader must
be able to handle every supported algorithm. What is the point of having
a standard format where some readers could read only part of them?
The zimwriter makes clusters of 1MB of html files and compresses them
with lzma2. Actually no xz overhead is used here. The 1MB cluster size
is choosen because lzma2 uses it. Larger clusters do not increase the
compression ratioa at all.
The writer has a fixed list of mime types, which are not compressed. The
mime types are "image/jpeg", "image/png", "image/tiff",
"image/gif"
and"application/zip". The writer do not try to compress them further but
they are stored as is in a separate cluster.
Tommi