The tarix format:

<headerline>
<512offset> <512length> <filename>
...

The headerline:

TARIX INDEX v<indexver> GENERATED BY <program and ver>

The current index version is 0, so a sample header line might look like:
TARIX INDEX v0 GENERATED BY tarix-0.0.1

The data lines:

Each data line is the 512-block offset in the tar archive in decimal, the
number of 512-blocks used by that file (not the same as the file length, but
how many blocks to seek forward to get to the next record, or how many
blocks to read out to get only that file), followed by the filename, and
then a newline.  512-blocks means that byte offset 512 in the tar archive
would be represented by a 512-offset of 1.
