/*
** aacgain - modifications to mp3gain to support mp4/m4a files
** Copyright (C) 2004-2010 David Lasker, Altos Design, Inc.
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
**/

AACGAIN VERSION 1.9

AACgain is a modification to Glen Sawyer's mp3gain, to support AAC 
(mp4/m4a/QuickTime) files as well as mp3 files. If you are not familiar with
mp3gain, stop reading this, and go to http://mp3gain.sourceforge.net

USAGE NOTES

1. BACK UP YOUR MUSIC FILES BEFORE USING AACGAIN! UNLIKE MP3GAIN, AACGAIN IS
   NOT COMPLETELY REVERSABLE. THE UNDO OPTION IS INTENDED TO RESTORE A MUSIC
   FILE TO BE FUNCTIONALLY EQUIVALENT TO ITS ORIGINAL STATE, BUT IT WILL NOT
   BE BIT-FOR-BIT IDENTICAL TO THE ORIGINAL FILE. IT IS POSSIBLE FOR APPLE
   TO CHANGE THE ITUNES MUSIC FILE FORMAT IN WAYS THAT ARE INCOMPATIBLE
   WITH AACGAIN, RESULTING IN CORRUPTED MUSIC FILES THAT CANNOT BE RESTORED
   TO THEIR ORIGINAL STATE. I AM NOT RESPONSIBLE FOR DAMAGED FILES.
2. AACGain supports files in the mp4/Quicktime file format. These files
   usually have a file extension of .mp4, .m4a, or m4v. Raw AAC files,
   files encoded with HE-AAC/SBR, or Apple Lossless files are not supported.
3. DRM'ed files purchased from the iTunes music store are not supported. You
   may convert these to .m4a format by burning them to a CD-ROM and importing
   them back into iTunes, or by using one of the underground methods to
   losslessly convert them to .m4a.
4. AACGain takes the same command line options as mp3gain - no
   changes have been made to the command usage.
5. If you rename the AACGain.exe executable to mp3gain.exe, it will work 
   with the Visual Basic front-end MP3GainGUI.exe.
6. When calculating or applying album gain, you may mix aac and mp3 files
   in the same command.
7. The /t (use temp file) option is ignored for aac files. A temp file
   is always used. The mp4v2 Optimize function is used to copy the
   processed file back to the original name. Experience has shown that this
   is required for processed music files to play on older iPods.
8. The /w (wrap) flag is ignored for aac files, since allowing an aac file
   to wrap will leave it in an unplayable state.
9. The /f (assume input file is an MPEG 2 Layer III) option is ignored
   for mp4/m4a/m4v files. If a file starts with a 'ftyp' atom, it is assumed 
   to be an mp4 container, even if /f was specified.
10. The /s i (id2v3) option is ignored for mp4/m4a/m4v files. The tags for
    these files are stored in iTunes metadata format as described below.
11. The following metadata tags will be added to your mp4/m4a files:
     - replaygain_track_gain
     - replaygain_album_gain
     - replaygain_track_peak
     - replaygain_album_peak
     - replaygain_track_minmax
     - replaygain_album_minmax
     - replaygain_undo
    These are all free-form metadata tags (moov.udta.meta.ilst.----)
    with 'data' text fields in the same format as the mp3gain
    equivalents. You may use AtomicParsley (download from sourceforge)
    to view the tags.
    
SUPPPORT
This is free software. No support is provided. 

You may try to post questions on the Hydrogen Audio AAC Tech forum:
http://www.hydrogenaudio.org/forums/index.php?showforum=14
I regularly monitor this forum, and use it to announce new releases
of aacgain.

You may email me questions, but there is no guarantee of a response.
If you have what you believe to be a valid .m4a/.mp4 file that is 
not processed correctly by aacgain, please attach it to your email.
I do not support the original mp3gain code.

WHAT'S NEW IN VERSION 1.9
a) Fixed a bug in mp4v2 which caused iTunes music video files
   to fail with "not a valid mp4/m4a file" error.
b) Gives a more meaningful error message when attempting to
   process Apple Lossless files.
c) Built with updated mp4v2 from Google Code, which should build
   error-free on modern Windows and Linux systems.
d) Built with updated faad2 code, which should build error-free
   on modern Windows and Linux systems.
d) Built with latest mp3gain version 1.5.2 sources checked into CVS,
   which include id3v2 tag support.
e) MSVC++ solution and project files have been converted to Visual
   C++ 2010 Express Edition.
    
WHAT'S NEW IN VERSION 1.8
a) Built with mpeg4ip/mp4v2 version 1.6.1. aacgain 1.7.1 was built with
   version 1.5.20. mp4v2 version 1.6.1 corrects problems that corrupted 
   video files containing Quicktime chapter markers.
b) Built with latest mp3gain version 1.4.7 sources checked into CVS. 
   The mp3gain changes made since 1.7.1 support sample rates up to 96000.
   Previous versions had a maxmimum sample rate of 48000.
c) Ignores faad2 "scalefactor out of range" errors. These errors resulted
   in "invalid file format" errors on apparently good files.

WHAT'S NEW IN VERSION 1.7.1
a) MSVC++ solution and project files have been converted to Visual
   C++ 2005 Express Edition. Other than the version number, no other 
   source code changes have been made.

WHAT'S NEW IN VERSION 1.7
a) If the total length of the directory plus file name path exceeded
   64 bytes, memory corruption would occur. This has been corrected.

WHAT'S NEW IN VERSION 1.6
a) Files with a 'cprt' (copyright) tag are now processed correctly.
   Previous versions of aacgain corrupted the metadata of files with a
   copyright tag.
b) AACGain now works on video or other files where the first audio track 
   has a track number of other than 1. Previous versions required the
   audio track to have a number of 1. AACGain will still only process
   the first audio track found on a file. Thanks to Arthur Yarwood at
   Sony Computer Entertainment Europe for this fix.

WHAT'S NEW IN VERSION 1.5
a) Running AACGain on Apple lossless or other unsupported file format 
   resulted in a crash with an unhandled exception. This is now fixed.

WHAT'S NEW IN VERSION 1.4
a) Temporary files are created in the same directory as the input file.
   Formerly they were created in the same directory that the program was run
   in. This solves a problem only seen on Unix systems where the temporary 
   file could not be renamed back to the original input filename, if the 
   input file was located on a different filesystem from where the program 
   was run. Windows users are unaffected by this problem and can continue to
   use 1.3.

WHAT'S NEW IN VERSION 1.3
a) Always uses the /t (use temp file) option, even if it is not specified
   on the command line. This resolves issues where processed files would
   not play on the iPod Shuffle.
b) Preserves original values of MP4 properties bufferSizeDB, maxBitrate and 
   avgBitrate. Without this change, mpeg4ip/mp4vs was recalulating the
   actual values of these parameters. This caused bitrate as displayed by
   iTunes to change slightly, i.e. songs ripped at 320KB would display as
   319KB.
c) Incorporates recent changes to mp3gain which prevent crashes when
   working with 48KB files on Linux.
d) Source code directory structure was reorganized to be compatible with mp3gain 
   CVS on sourceforge. Thanks to Glen Sawyer, the AACGain source code is now 
   hosted on sourceforge's CVS repository as part of the mp3gain project.

WHAT'S NEW IN VERSION 1.2
a) Fixes compatibility issue with MP3GainGUI version 1.2.5 or 1.3.4.
b) All temporary files created are erased.
   
WHAT'S NEW IN VERSION 1.1
a) Multi-channel and mono files now work.
b) Fixes compatibility issues with MP3GainGUI:
   - /o option always outputs Album gain
c) /f option is ignored for AAC files - see usage notes below.
d) Uses portable versions of all library functions, and has been
   successfully compiled under Linux. Thanks to Prakash Punnoor
   for his help with this.
   
BUILDING AACGAIN FOR WINDOWS FROM SOURCE CODE

MSVC++ solution and project files have been converted for Visual C++
2010 Express Edition. The MVSC++ 2005 and 6.0 project and solution files
are no longer being maintained. It is now required to use VC++ 2010 to
build aacgain for Windows.

In order to build AACGain for Windows, the following components are 
required. You may download them from the links listed below:

a) aacgain

   Thanks to Glen Sawyer, aacgain source code is checked into the sourceforge
   CVS repository as part of the mp3gain project. A CVS client is required.
   See the instructions at http://sourceforge.net/cvs/?group_id=49979. The
   commands to check out the aacgain source code are:
   cvs -d:pserver:anonymous@mp3gain.cvs.sourceforge.net:/cvsroot/mp3gain login 
   cvs -z3 -d:pserver:anonymous@mp3gain.cvs.sourceforge.net:/cvsroot/mp3gain co -P aacgain

b) mp3gain
   You may use either the zipped version 1.5.1 source code at
   http://mp3gain.sourceforge.net/download.php or check out the code from
   the latest CVS. The CVS commands to check out the mp3gain source code are:
   cvs -d:pserver:anonymous@mp3gain.cvs.sourceforge.net:/cvsroot/mp3gain login
   cvs -z3 -d:pserver:anonymous@mp3gain.cvs.sourceforge.net:/cvsroot/mp3gain co -P mp3gain
   The latest version of aacgain was build from mp3gain source files from CVS
   that were most recently modified on May 19 03:48:34 2010 UTC.
   
c) faad2
   aacgain was built using the the FAAD2 release 2.7 dated 2009-02-10
   downloaded from http://sourceforge.net/projects/faac/files/.
   
   Download any of the faad2-2.7 source files and expand the archive as a peer
   to the aacgain directory. Rename its top-level directory to faad2.

   Due to the way aacgain is programmed, using modified copies of faad2's
   decoder.c and syntax.c, use of any earlier or later version of faad2
   is not recommended.
   
d) mp4v2
   As of version 1.9, aacgain uses the mp4v2 code found at
   http://code.google.com/p/mp4v2/. aacgain is built using the mp4v2 r355
   snapshot. aacgain uses the r355 snapshot, rather than the official
   release 1.9.1, due to its use of iTMF tags.
   
   Download the tarball mp4v2-trunk-r355.tar.bz2, and expand the archive.
   Rename its top level directory to mp4v2.
   
   Due to the patches described below, use of any earlier or later version
   of mp4v2 is not recommended.
   
   A patch file mp4v2.patch is in the aacgain directory. This patch 
   fixes two issues:

   1) The first 2 groups of patches to mp4track.cpp remove code which
       recomputes the maximum and average bitrates. If this code is not
	   removed, a file with a nominal bitrate of 128KB may have its bitrate
	   changed to something like 131287.

   2) The last group in the patch to mp4track.cpp fixes a bug which prevents
      iTunes music videos from being processed correctly. See the comments
	  in the patch for details. I  reported this bug to the mp4v2 developers,
	  and it is fixed in the latest mp4v2 svn. However, the Visual Studio project
	  files in svn will not convert to VC++ Express, due to their use of features
	  only in the full (paid) version of Visual Studio. Therefore, I am
	  using the r355 tarball, and patching the bug myself.

   cd to the aacgain directory where mp4v2.patch is located. Apply the patch with 
   the command

   patch -p0 <mp4v2.patch

   If you don't care about the above issues you may skip applying this patch.
   
The components must be arranged in the following directory hierarchy:
-- aacgain containing aacgain.sln/.vcprojx and source files
-- faad2 
   -- libfaad containing libfaad.sln/.vcproj
-- mp4v2 (rename its top directory from what was in the tar.bz2 file)
   -- vstudio9.0 containing mp4v2.sln
   -- src and other directories
-- mp3gain
   -- mpglibDBL
      
Earlier versions of aacgain built mp4v2 as part of the aacgain
solution. However, the mp4v2 from Google Code requires
massive changes to its include paths to do this. It is much easier
to build it separately, and then just link its library
into the aacgain solution. In order to build libmp4v2,
open mp4v2\vstudio9.0\mp4v2.sln in VC++2010. Allow the conversion to
complete. Delete any projects marked "(unavailable)". Build the 
"Debug Static" and "Release Static" configurations.

Open faad2\libfaad\libfaad.sln in VC++2010 and allow the conversion to
complete. Don't build libfaad at this point; it will be built as part of 
aacgain.

Open aacgain/aacgain.sln. There should be 3 projects in your solution:
1. aacgain
2. libfaad
3. mp3gain

Make the following changes to the libfaad project properties:
a) Change the C++/Code generation/Runtime Library property for libfaad to
   "Multi-threaded Debug (/MTd)" for debug build and "Multi-threaded (/MT)"
   for release build. 
b) Change the C++/Optimization/Whole Program Optimization property to
   YES(/GL) for the release build only.
c) Change the Librarian/General/Link Time Code Generation property
   to YES(/LTCG) for the release build only.

At this point, you may press F7 and cross your fingers:-)

The aacgain.exe executable will be found in the aagain/Debug or 
aacgain/Release directories.

BUILDING AACGAIN FOR UNIX (LINUX/MAC OS X) FROM SOURCE CODE

Thanks to Prakash Punoor, the source code is portable, 
and has been compiled for Linux and Mac OS X. 

I now have access to both Linux and Mac systems, so I have modified
Prakash's scripts to build correctly with the latest code changes.

See the file aacgain/linux/README.linux for detailed Linux/Mac build 
instructions.

HOW AACGAIN WORKS

mp4v2 is used to parse the mp4/QuickTime file format, to
read individual samples so that they can be passed to faad2, and to
read and write replaygain metadata tags.

faad2 is used to de-compress and decode the aac frames into linear 
PCM for analysis by the replaygain algorithm.

Files syntax.c and decoder.c are slightly modified versions of the
corresponding files from faad2. The modifications allow the offsets
and original values of the global_gain fields to be saved. Since the
modified functions were declared static in libfaad, I am able to use
my own modified copies of these functions without getting duplicate
definition link errors.

mp4v2 is used to apply any gain changes needed. It does this as follows: 
a) creates a new audio track
b) copyies the samples from the original audio track to the new track
   with the global_gain fields appropriately modified
c) deletes the original audio track
d) modifies the trackId property of the new track, and the nextTrackId
   property of the moov atom, to be the same as in the input file.

aacgain.cpp is a wrapper for the above functionality.

mp3gain.c has been modified to call aacgain when the symbol AACGAIN is
defined. mp3gain versions 1.5 and later have this modification included.

ACKNOWLEDGEMENTS

I am a total newbie to digital audio, and I created AACGain primarily
as a learning exercise. I couldn't have done it without the help of others:

1. Thanks to the user community at hydrogenaudio.org and audiocoding.com,
   especially Menno and Hans-Jürgen.
2. Thanks to Bill May for helping me get started with mp4v2.
3. Thanks to Prakash Punnoor, Hardloaf, Ben Allison, and Miguel Angel Alvarez
   for their help with Linux and Mac.
4. Last, but not least, thanks to Glen Sawyer for creating mp3gain.

Dave Lasker
dave@altosdesign.com
