A common problem found by consumers in the Web-centric world of today is converting media files from one format to another for a variety of reasons. With the explosion of digital audio playback devices in the past decade, the need to convert between audio formats has never been greater. MPEG-4 is the most widely accepted ISO standard for multimedia formats on the Web, that offers the same video and audio quality found on DVDs and CDs respectfully, when compared to its predecessors MP-2 and MP-3. A problem with the MPEG-4 CODEC, however, is that although it is optimized for web streaming and combined multimedia playback, many consumers have music playing software and devices which do not accept the MPEG-4 format. The majority of legacy music software and playback devices only accept the MPEG-3 standardized format for audio.

Defining the MPEG-4 Standard

MPEG-4 is the international standard for multimedia container formats on the Web. Developed as a collaborative project between both industry partners as well as competitors, MPEG-4 has the capability to combine various forms of media in a single file. The media container can contain video, audio, as well as embedded 3D content in X3D format. The most common use of MPEG-4 since its adoption as an international standard is to combine audio and video files in an Internet stream. An MPEG-4 file ends with the .mp4 file extension and closely mimics the Apple .MOV file format except that it provides support for including meta data descriptors for the media object as well as architectural support for additional features. The audio component of MPEG-4 files is referred to as the Advanced Audio Coding (AAC) format. AAC utilizes a compression algorithm that is significantly more efficient than its legacy predecessor, MP-3 resulting in smaller file sizes, but an exponential increase in audio quality.

MPEG-4 Identity Crisis

A problem that arose with the current MPEG-4 format is that files with the extension .mp4 do not have a means for a software application to be able to tell what types of files are contained within the MPEG container file. Even though the file types can be detected by programs after conducting basic MPEG API calls, the loss of efficiency resulted in Apple Inc using the .M4A files extension for MPEG-4 files, which only contain audio files. The majority of MPEG-4 compatible software now recognizes both file extensions and will simply fail to play the file if it does not contain an audio component to the file. Industry has also begun to mimic the Apple model with MPEG-4 file extensions in order to indicate what type of MPEG-4 file an application has loaded. Common MPEG-4 files extensions are:

What is the MPEG-3 Format?

MPEG-3 or MP-3 as most people recognize the format, is the most widely recognized audio file format. It can only be used for digital audio encoding and has become the recognized standard format for digital music players. The format was originally developed by the Moving Picture Experts Group (MPEG) that was comprised of engineers from around the world. MPEG-3 was formally recognized as the international standard (ISO) in 1991 as the Internet was starting to be more widely used. The advance in technology with the MP-3 audio file format was due to the use of a compression algorithm which permitted loss of audio quality in order to achieve smaller file sizes. The generally acceptable level of quality for an MP-3 to sound as good as a CD is 128 kbits/second before a user can notice a loss of quality. As a result, a MP-3 file is normally 10% of the size of a music file found on a CD. The compression algorithm used when creating a MP-3 file closely mimics that used by the 2-D imagery format .JPEG.

MPEG-3 Limitations

Although MP-3 is the most popular digital audio format in the world, there are still a number of limitations inherent in the design of the format. These are:

• Percussion sounds can sound distorted or smeared due to the low threshold of the time resolution inherent in the file format.

• Any pre-echo issues with the music recording are amplified due to the internal file structure of the MP-3 file format.

• It is difficult for the MP-3 format to handle frequencies in audio over 15.5 kHz which do not scale well in the format.

• Stereo playback is encoded on a frame-by-frame basis resulting in loss of quality.

• There is no defined standard for re-playing audio without perceptiblegaps resulting from file encoder or decoder delay.

• There are significant patent issues for companies that desire to produce commercial encoding and decoding (playback) products for MP-3. These were resolved with MPEG4 but have been the source of a number of the issues with the various MP4 variants on the market today.

How to Convert from MPEG-4 to MPEG-3 Format

There are a number of means to convert MPEG-4 encoded audio to MP-3 format. iTunes can be used to convert the audio file formats though it can take time to bulk convert files. To convert a large number of MP-4 encoded files, using a audio batch conversion software package will save a significant amount of time.

Converting MPEG-4 to MPEG-3 Format Using iTunes

• Step 1 – Download and install iTunes if not already on the computer from iTunes.com

• Step 2 - Change the import settings on iTunes to import music files in MP-3 format by going to the “Edit->Preferences->General” file menu options and selecting the “Import Settings” menu button. Select the “Import Using” menu option and change the setting to “MP-3 Encoder” from the default .AAC.

• Step 3 – Upload your audio content into iTunes if you don’t already have it in the iTunes library.

• Step 4 – Create an audio CD with the content to convert to MP-3.

• Step 5 - Upload the files from the CD to iTunes. This will load non-encrypted audio to the iTunes library to make use of the Apple .MP3 export utility. If you know the audio is not encrypted then steps 3 and 4 may be omitted.

• Step 6 -Right click the file or files that are going to be converted and select the “Convert to MP-3″ menu option.

The iTunes conversion method is free except for having to burn a real or virtual CD of the music to remove the file-type protection inherent in iTunes for purchased music. Another option for batch converting MP4 to MP3 file formats is to use a batch converter.

How to Batch Convert MPEG-4 Audio Files to MPEG-3 Format

JHymn software is an audio batch conversion software application that is available to use for free in trial mode or a paid version for additional file modification features. The steps to batch convert MPEG-4 encoded files to MPEG-3 using JHymn are:

• Step 1 – Download the MP-4 to MP-3 Converter and install on your computer. It is compatible for Mac as well as Windows computers.

• Step 2- Select the “Add Files” menu button in the application. Multiple files can be selected in the file open dialog.

• Step 3 – Choose the file menu “Option” button to choose the desired conversion format, sample rate, bit rate, channel, and destination file to save the MPEG-3 file when complete.

• Step 4 – Left Click the “Convert” button in the application to convert all of the selected MPEG-4 files to MP-3 format.

Other Tools to Convert MPEG-4 Files

AVS Audio Converter

Easy CD-DA Extractor 9.0.1 build 2 by Poikosoft

River Past Audio Converter