UnpackMP4 AVI - bitstream unpacker for DivX/XviD AVIs

A Java Clone of UnpackCL / MPEG4Modifier by Moitah

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General

UnpackMP4 AVI (shortname: UnpackMP4) is a Java rewrite of UnpackCL (written in C# by moitah). UnpackCL is a command line version of the excellent MPEG4Modifier tool (again, written in C# by moitah) that's used to detect and unpack AVIs that are encoded in DivX or XviD and have packed bitstream. Unpacking is useful when you want to play the AVI on many standalone players, since AVI with packed bitstream play as if they were recorded at 10fps (they look jumpy).

UnpackMP4 version 1.2 is based on UnpackCL v1.1.2 and has the exact same functionality except for the following:

A few more options are available on the command line. For example, multiple files can be processed in a single execution of UnpackMP4
Some portions of the program have been rewritten to improve performance.

Downloading

You may download the executable JAR file or a zipped source of UnpackMP4. The source comes as an Eclipse 3.1 project.

If you choose to download and view the source, please remember this is a rough port from C#, hence many of the names start with an upper-case letter, which is against the Java standard

Running

Depending on the arguments, UnpackMP4 can be used to unpack (or check) a single file or multiple files. To unpack a single file, use the following arguments:

java -jar unpackmp4.jar [-i] source-path [dest-path]

In this case, the arguments are the same as in UnpackCL:

`-i`	Display detailed information about the video.
`source-path`	The path of the avi file to be unpacked. In the file is already unpacked, nothing will be performed.
`dest-path`	The path of the avi file to be created (the unpacked version). If this path is not specified, UnpackMP4 will just check if the source-path is unpacked or not.

To unpack (or check) multiple files, use the following arguments:

java -jar unpackmp4.jar [-i] [-s suffix] [-d dest-folder] [-c] source-path1 source-path2 ...

The -i argument works as before, and in addition:

`-s suffix`	Process all specified files, derive the unpacked file names by appending suffix to the original file name. If the file name ends with `.avi` the suffix will be added before the `.avi`. For example, if we use `-s .unpack`, `mymovie` will be unpacked into `mymovie.unpack`, and `hismovie.avi` will be unpacked into `hismovie.unpack.avi`
`-d dest-folder`	Process all specified files, and store the unpacked files i the `dest-folder` folder.
`-c`	Check all files and report if they are packed or not. Do not unpack.
`source-path1 source-path2 ...`	The list of files to unpack or check. Wildcards are not allowed but fortunately, using (for example) `*.avi` in bash (and other shells, I assume) translates to the list of all files, so it works in Linux (and possibly other Unix flavors) using a little help from the shell.

Performance

While converting to Java, I tried to improve performance to sweeten the deal of those who already use the wonderful UnpackCL (like myself) and consider switching to UnpackMP4. The result is presented in the following table:

Test	UnpackCL on Windows	UnpackMP4 on Windows	UnpackMP4 on Linux
Unpack 5 packed files, 350MB each, using 5 calls within a bat/sh file	0:05:51.7	0:03:00.9	0:03:36.7
Check 5 packed files, 350MB each, using 5 calls within a bat/sh file	0:00:50.7	0:00:50.1	0:01:16.9

Notes:

The results show that UnpackMP4 runs almost twice as fast when unpacking, but at the same speed when no unpack is performed. This might be because I concentrated on the code in which most of the time is spent - unpacking.
The tests were run on a Compaq nw8000 laptop with 1GB of memory. This computer is set for dual boot - both Windows XP Professional and Linux (Debian).
The results are based on the average of 10 execution of each test. The Windows tests were interleaved. The Linux tests were performed later (I didn't want to reboot that many times...)
I don't have a comparison to UnpackCL on Linux using Mono. I'm realy a novice in Linux, and don't know yet what Mono is. I translated UnpackCL to Java, since I knew this would run on Linux (and I know Java inside-out), and I decided to drop Windows on my home computer.

Conversion Information

For those who care (probably not too many), here are some notes regarding the conversion from C# to Java:

Generally speaking, the conversion is really simple. Java and C# are pretty source-compatible (and for good/bad reasons, you decide). Most of the changes were simple find/replace all.
I know nothing about the internals of AVI and MPEG4 format (unlike moitah). I did a stupid source conversion and fixed bugs by addressing exceptions and comparing the output of UnpackCL and UnpackMP4. The output is exactly the same. Since I don't know anything about the file format, that's the only way I could do it.
UnpackCL uses a random access file to read and write the file. Java's RandomAccessFile is notoriously slow. I noticed that in most cases the file access is sequential, so I wrote a wrapper that buffers reads and writes to improve I/O performance. The same trick might be used to improve the C# code (If random access is also slow there).
UnpackCL includes an implementation of a bit-stream that's used to process many parts of the file (VOPs, VOLs and other nasties). I found a few places to improve performance there. Again, these improvements can be ported back to C#.

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