MPEG-4 Explain this

[herojordan]

I don’t understand as well as I should. MPEG-3 was pretty ubiquitous and only meant music (or am I wrong?) But MPEG-4 seems to be a totally different animal. Itunes uses it? Videos use it? Music uses it? Please fill in an otherwise informed (wannabe) audiophile with the details. Feel free to throw around such terms as: container file, surround sound, DRM, audio/video codecs, etc.

Thanks!

[Telemark]

MPEG-4 is a standard used primarily to compress audio and visual (AV) digital data. Introduced in late 1998, it is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) under the formal standard ISO/IEC 14496. The uses for the MPEG-4 standard are web (streaming media) and CD distribution, conversation (videophone), and broadcast television, all of which benefit from compressing the AV stream.

MPEG-4

[Gary_Robson]

In a nutshell, MPEG 1 and 2 are video encoding standards (and they do include audio). To be precise, MPEG is the name of the organization that came up with the standards (the Motion Picture Experts Group). MPEG 3 was developed as an audio encoding standard. People associate it with music because most of the audio files that your average person encounters are music.

MPEG 4 is a video/audio standard like MPEG 1 and 2.

[gazpacho]

I am pretty sure that MP3 audio files are more formally known as MPEG1 layer 3. So mp3s are defined in the MPEG1 standard.

[kellner]

@gazpacho

I am pretty sure that MP3 audio files are more formally known as MPEG1 layer 3. So mp3s are defined in the MPEG1 standard.

Yes, and MPEG3 was supposed to become a group of standards (comparable to MPEG1, 2 and later 4) for HDTV but it never got very far.

[neutron_star]

@gazpacho

I am pretty sure that MP3 audio files are more formally known as MPEG1 layer 3. So mp3s are defined in the MPEG1 standard.

Correct. The real MPEG-3 spec barely made it out of the starting gate.

[scm1001]

All these formats are not single streams like raw video. They are essentially a method of encoding video and contain in the file such infomation as video size, rate, refresh method, compression method and separate audio as well as the data streams themselves. As I understand it MPEG1 and 2 are quite rigid in the compression method and video rates etc and dont have much more than the above. They were design for fixed applications, namely video recording (VCR) bit rates and HDTV rates.

The world is much more complicated now. MPEG4 is very flexible in that the compression codec can vary, almost any screen size or rate etc is allowed. This is perfect for the new devices with small screens (ipods, phones). As well in principle much more can be encoded into the file, including subtitles, 3D rendering etc. the problem is that with such flexibility comes a price in compatibility, e.g. my ipod refuses to play many well formed mp4 files presumeably because the wrong codec or refresh rate is specified. As well the patent situation is not clear - e.g. Apple was sued over its use of some mp4 technology.