M4A to AAC
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| - Information about AAC |
| Id |
| 1 |
| File extension |
| aac |
| File category |
| Audio |
| Stands for |
| Advanced Audio Coding |
| Developer |
| Bell Labs, Fraunhofer IIS, Dolby Laboratories, LG Electronics, Sony Corporation (Combined Efforts) |
| Overview |
| AAC is the descendant of the MP3 format. It provides better sound quality using a similar bit rate as of MP3. Besides this, it uses lossy data compression but it has high standards of audio quality than of MP3. We can find this format on a number of platforms and Apple's iTunes is one such example that uses it as default audio format. Size of its file is much smaller which is approximately one-tenth of MP3 file. It also neglects the redundant information that is not even processed by the human ear and is often not noticed. Although, this format was introduced as MPEG-2 Part-7, yet, standardization was done by ISO/IEC as a part of the MPEG-2 and MPEG-4 families. It is also termed as MPEG-2 NBC (Non- Backward Compatible) because it is incompatible with MPEG-1 audio formats i.e. MP1, MP2, MP3. |
| Technical description |
| Modified discrete cosine transform(MDCT) algorithm is used by AAC which ensures that it provides high compression efficiency. MPEG-2 PART-7 has three default profiles namely Low Complexity (LC), Main Profile (Main) and Scalable Sample Rate (SSR). These profiles come with Perceptual Noise Substitution which enhances coding efficiency and provides excellent audio quality. Furthermore, it uses Auditory Masking to ignore the surplus information. This codec has come up with advanced features which are not available in the predecessor. These include additional sample rates ranging from 8 to 96 kHz, 48 Channels, better efficiency with a simpler filter bank, higher coding efficiency for stationary signals and higher coding accuracy for transient signals. |
| Links |
| wikipedia.org |
| - Information about M4A |
| Id |
| 4 |
| File extension |
| m4a |
| File category |
| Audio |
| Stands for |
| MPEG-4 PART 14 or MPEG-4 Audio |
| Developer |
| Apple |
| Overview |
| It is an audio file which uses AAC (Advanced Audio Coding) compression. Also, it is one of the formats of MPEG-4. It should be noted that MPEG-4 codec is used both for video and Audio. But M4A is specially designed by Apple for audio files only that is why it is used to store audiobooks, podcasts and songs. As sound files are encoded using AAC compression and this results in a reduction of file size and it also produces a very good quality of audio. Whenever somebody purchases music from the iTunes store then it is always available in this format. Many believe that MP4 and M4A are similar extensions, however, it’s not the truth. MP4 files can store both Audio and video files whereas the other one is entirely made for Audio files. |
| Technical description |
| These files are improved version of MP3 as it has the ability to store data without any loss. The audio files are completely reversible that is they can be inverted to their original copies with the same size. Besides this, these files does not have copyright protection whereas MP4 files are protected and they use DRM(Digital Rights Management) technology to enforce this protection policy. Due to this, one can copy these audio files effortlessly. These files have come with advanced features which include smaller sample block sizes, perception-based compression and bigger block sizes in stationary signals. There are a number of applications that support this extension. For example:- Microsoft Windows Media Player, VLC Media Player, Quicktime player, Microsoft Zune and Apple iTunes etc. |
| Links |
| wikipedia.org |
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