Probably won't interest many people, but meh, if you wanted to know the status of the "dead" JISO format, here's probably the final update:

Uncle Jam Wrote:Hi guys

This is my latest and probably last release of my JSO & DAX plugin for Devhook. I don't know if it's of any help for anybody, if anybody but me still uses Devhook. Anyway, for those who do, you might want an alternative to CSO file format, for better compression and/or better speed. This is what my plugin offers. No plan for 3.XX OE FW plugin but, hey guys, the source code is included so help yourself :p .

This is an extract of the README.txt file you will find in the archive.

Install Instructions
====================

Environment
-----------

The plugin works for Devhook 0.46 and 0.52 on a PSP firmware version 1.5.

No support for modded versions of Devhook.
No support for OE firmware versions (as I have no way to test).

Devhook 0.46 and/or 0.52 are assumed already installed.

Instructions
------------

In this archive, you will find the following folder structure

full/

umdciso.prx (Full version with ISO/CSO/DAX/JSO file support, memory footprint about 46 kbytes)
dax/

umdciso.prx (DAX version with ISO/CSO/DAX file support, JSO file support removed, memory footprint about 36 kbytes)
jso/

umdciso.prx (JSO version with ISO/CSO/JSO file support, DAX file support removed, memory footprint about 15 kbytes)
pc/

jiso.exe Compression/Decompression utility executable for Windows.

Devhook 0.46 :

Drop the binary file umdciso.prx in [MS-ROOT]/dh/kd and replace the existing one.

Devhook 0.52 :

Drop the binary file umdciso.prx in [MS-ROOT]/dh/05/kd and replace the existing one.

Usage Instructions
==================

Usage: jiso.exe -c|d [-s] [-a algorithm] [-b size] [-l level] [-t threshold] -i inputfile -o outputfile

  -a algorithm : Compression algorithm (lzo, zlib), default is zlib
  -b size      : Block size (2048, 4096, 8192, 16384, 32768), default is 8192
  -c|d         : Compress | Decompress
  -h           : This help page
  -i inputfile
  -l level     : Compress level (1=fast/large - 9=small/slow), default is 9
  -o outputfile
  -s           : Simulation mode enabled
  -t threshold : Compress threshold (0.0 - 1.0), default is 1.0
  -v           : Show version
  -B           : Block header mode enabled
  -C           : Compression threshold NC area
  -N           : NC area minimum size, default is 2048 kbytes
  -S           : Sound files NC area
  -V           : Video files NC area

General information
===================

JSO & DAX plugin for Devhook is a plugin for Devhook version 0.46 and 0.52 to support DAX and JSO file formats in addition to ISO and CSO file formats.

DAX is a former file format introduced by Dark_Alex in DaxZiso loader.

JSO is a new file format introduced by myself with the following features :
- support of both lzo and zlib compression, lzo is a bit faster than zlib for decomppression but files are about 10% bigger
- support of frame size of 2048 bytes (like CISO), to 32768 bytes for better compression
- support of DAX-like NC areas
- memory footprint is around 15 kbyte

Source code included based on Devhook 0.46 by Booster.

/pctool/jiso

Contains the source code for jiso compressor utility.
/umdciso

Contains the source code for the jiso & dax plugin. Edit makefile to enable/disable JSO/DAX/CSO support. All formats enabled by default.

- Source: [Maxconsole Forums]

:dl: Download (note you must be a member of Maxconsole to download from that link; I am unable to upload the file due to my connection)

OE is not native support, i tried flash too, but doesn't work.

it's quite troublesome to decode/encode the files into JSO too. :(

Yeah, I agree.  JSO was kinda pointless - CSO works fine most of the time.  It was an interesting idea I guess, as it supports two compression algorithms.  Mainly too late, and lack of support.