MP3 to M4A: Convert Audio from MP3(MPEG Layer-3) to M4A(MPEG-4 Audio) with River Past Audio Converte
2007-10-16

What is MP3?
(MP3) A digital audio compression algorithm that acheives a compression factor of about twelve while preserving sound quality. It does this by optimising the compression according to the range of sound that people can actually hear. MP3 is currently (July 1999) the most powerful algorithm in a series of audio encoding standards developed under the sponsorship of the Moving Picture Experts Group (MPEG) and formalised by the International Organization for Standardization (ISO).

MP3 is very different from Layer 2, using an additional MDCT layer to increase frequency resolution. Its scale factor groups are more optimised for the human ear, and it uses nonlinear sample quantisation and Huffman coding. MP3 files (filename extension ".mp3") can be downloaded from many World-Wide Web sites and can be played using software available for most operating systems (also downloadable), e.g. Winamp for PC, MacAmp for Macintosh, and mpeg123 for Unix. MP3 files are usually downloaded completely before playing but streaming MP3 is also possible. A program called a "ripper" can be used to copy a selection from a music CD onto your hard disk and another program called an encoder can convert it to an MP3 file.

Windows ships with limited MP3 encoding support. The output sample rate is limited to 24khz and the bitrate is limited 56kbps. However, many add-on packages from open source community make it possible to encode at higher sample rate and bitrate.

A commonly used open source codec is LAME. LAME comes in different forms, including a ACM (Audio compression manager) codec and a DLL (lame_enc.dll). Caution: LAME ACM does not work well on many computers, regardless which software is loading it. It is best to avoid installing LAME ACM and use lame_enc.dll instead.

MPEG.ORG is an excellent source for additional information on MPEG format and usage.



What is M4A?
Because of its exceptional performance and quality, Advanced Audio Coding (AAC) is at the core of the MPEG-4, 3GPP and 3GPP2 specifications and is the audio codec of choice for Internet, wireless and digital broadcast arenas. AAC provides audio encoding that compresses much more efficiently than older formats, such as MP3, yet delivers quality rivaling that of uncompressed CD audio.



Additional Requirements
To convert from MP3(MPEG Layer-3) to M4A(MPEG-4 Audio) audio with River Past Audio Converter, you must have River Past MPEG-4 Booster Pack installed. You will also need to install QuickTime.


Launch River Past Audio Converter
Once River Past Audio Converter is installed properly, launch Audio Converter.

Add File
Click on the "Add File" button on the tool bar. The standard file open dialog appears. Select "MP3 - MPEG Layer-3 Audio" in its "Files of type" combo box.

Select the file you want to convert and click "Open". The file will be added to the conversion file list.

Select output format
Use the setting panel on the bottom of the window to control the output format. Click on the toggle to the left of the "Format" label to expand the panel. Select "M4A - MPEG-4 Audio" as the "Audio Type".

You can change the sample rate, channel (stereo or mono) and bits/sample, and bitrate.

Note: To convert to MPEG-4 audio, you must have River Past MPEG-4 Booster Pack installed.

Select output directory
Expand the "Output Directory" panel. Use the "Browse" button to select an output directory.

Convert
Click the "Convert" button on the tool bar.