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MPEG Audio Formats

MPEG Audio Formats. Jason Leung Wednesday, February 5, 2014. Introduction – MPEG. Moving Picture Experts Group Officially: ISO/IEC JTC1/SC29 WG11 Established 1988 Sets standards for audio/video transmission. Official logo. Leonardo Chiariglione , Chair. Hiroshi Yasuda

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MPEG Audio Formats

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  1. MPEG Audio Formats Jason Leung Wednesday, February 5, 2014

  2. Introduction – MPEG • Moving Picture Experts Group • Officially: ISO/IEC JTC1/SC29 WG11 • Established 1988 • Sets standards for audio/video transmission Official logo Leonardo Chiariglione, Chair Hiroshi Yasuda (Nippon Telegraph and Telephone)

  3. MPEG Standards MPEG-1 Coding of moving pictures and associated audio at up to 1.5 Mb/s MPEG-2 Generic coding of moving pictures and associated audio MPEG-4 Coding of audio-visual objects MPEG-7 Multimedia content description interface MPEG-21 Multimedia framework MPEG-A Application formats MPEG-B MPEG system technologies MPEG-C MPEG video technologies MPEG-D MPEG audio technologies MPEG-E MPEG multimedia middleware MPEG-V Media context and control MPEG-M Multimedia service platform technologies MPEG-U MPEG rich media user interface MPEG-H High efficiency coding and media delivery in heterogeneous environments MPEG-DASH Dynamic Adaptive Streaming over HTTP

  4. MPEG-1 • Coding of moving pictures and associated audio at up to about 1.5 Mbit/s • Standard for lossy compression • VHS-quality video 26:1 compression ratio • CD-quality audio  6:1 Part 1 System Part 2 Video Part 3 Audio Part 4 Conformance testing Part 5 Reference software

  5. MPEG-1, Part 3: Audio • Lossy compression • Psychoacoustic model (perceptual coding) • Reduces/discards parts we can’t hear • Outside audible range • Masking • Compression ratios MPEG-1 192 kb/s 7:1 CD 1411.2 kb/s 9:1 160 kb/s 11:1 128 kb/s

  6. MPEG-1, Part 3: Audio • Very strictly defines output/decoder • Does not define encoding • Different encoder = Different output Digital audio signal Analysis Filterbank Quantization and Coding Encoding of bitstream Perceptual Model Encoded Bitstream (Brandenburg and Popp 2000) Synthesis Filterbank Inverse Quantization Decoding of bitstream Audio out

  7. MPEG-1, Part 3: Audio • 3 hierarchical layers (Ambikairajah, Davis, Wong 1997)

  8. MPEG-1, Part 3: Audio • Does this mean MP3 is the best? • MP2 preferred in Digital Audio Broadcasting1 • Lower delays = faster transmission • MP3 only for Internet broadcasts • Bandwidth considerations • MP2 scores higher in subjective testing2 • Comparison based on expected quality • [MP2] 224 kb/s vs. [MP3] 192 kb/s • Better for complex, random, transient signals • Voice, orchestra, percussion, applause European Broadcasting Union. 2007. EBU Tech 3324. pp. 7–9. Ibid. pp. 51.

  9. What’s next? • MPEG-1 is 26 years old • Designed 1988–1992 (published 1993) • Designed for studio use • MP3 not meant to be standalone • Designed for equipment of the early 90s • MPEG-2 • Designed 1990–1995 (published 1996) • Part 3: Audio – updated MP2, MP3 slightly

  10. Advanced Audio Coding (AAC) • MPEG-2, Part 7 • First published 1997 • Successor to MP3 • More sampling frequencies: 8–96 kHz • Up to 48 channels • MP3 has 2 (MPEG-1) or 5.1 (MPEG-2) • Higher efficiency for stationary signals • Higher accuracy for transient signals

  11. Advanced Audio Coding (AAC) • Revised as MPEG-4, Part 3: Audio (1999) • New tools • Perceptual Noise Shaping • Noise  pseudo-random data • New formats • AAC-LD (low delay), 2000 • MPEG-4 SLS (Scalable to Lossless), 2006 • MPEG-4 ALS (Audio Lossless Coding), 2006

  12. Conclusions • MP3 here to stay (for a while) • Omnipresent, default format • Playback guaranteed • Berger 2009: iPod generation prefers MP3 fidelity over CDs • AAC is default format for: • YouTube, iTunes, Nintendo 3DS/DSi, PS3 • HD content (MP4 = MPEG-4 format) • Not finalized (as of Jan 2014)

  13. References • Ambikairajah, E., A.G. Davis, and W.T.K.Wong, 1997. Auditory masking and MPEG-1 audio compression. Electronics and Communication Engineering Journal 9(4): 165-175. • Brandenburg, K. 1999. MP3 and AAC Explained. In Proceedings of AES 17th International Conference on High Quality Audio Coding. Florence, Italy. • Brandenburg, K., and H. Popp, 2000. An introduction to MPEG layer-3. EBU Technical Review. June: 1-15. • European Broadcasting Union, 2007. EBU Evaluations of Multichannel Audio Codecs. EBU Tech 3324. Geneva, Switzerland. • Liebchen, T. 2004. An Introduction to MPEG-4 Audio Lossless Coding. Proceedings of the ICASSP III: 1012-1015. • Pan, D. 1995. A Tutorial on MPEG/Audio Compression. IEEE Multimedia, IEEE Computer Society 2(2): 60-74. • Wikipedia!

  14. MPEG Audio • MPEG-1 • Part 3: Audio (MP1, MP2, MP3) • MPEG-2 • Part 3: Audio • Part 7: Advanced Audio Coding (AAC) • MPEG-4 • Part 3: Advanced Audio Coding • MPEG-D • Part 1: MPEG Surround • Part 2: Spatial Audio Object Coding • Part 3: Unified Speech and Audio Coding

  15. Psychoacoustic Model • Masking effect: loud sounds cover soft sounds (Wikipedia. Psychoacoustics. http://en.wikipedia.org/wiki/File:Audio_Mask_Graph.png)

  16. MPEG-1, Part 3: Audio • 2 channels • 3 hierarchical layers • Increasing complexity, efficiency • [MP2] 192 kb/s = [MP3] 128 kb/s (quality) • Backwards-compatible

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