| mp4-sa-> sfront reference manual-> audio drivers |
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Audio Driver Functionsasys_osetup asys_isetup asys_iosetup asys_preamble asys_putbuf asys_getbuf asys_main asys_is/index.html">read our papers on the topic, and see related work on Network Musical Performance. |
What is MPEG-4 Structured Audio?MPEG-4 Structured Audio (MP4-SA) is an ISO/IEC standard (edited by Eric Scheirer) that specifies sound not as sampled data, but as a computer program that generates audio when run. Computer scientists call this approach Kolmogorov encoding. MP4-SA combines a powerful language for computing audio (SAOL, pronounced "sail") and a musical score language (SASL, pronounced "sassil") with legacy support for the MIDI format. MP4-SA also defines an efficient encoding of these elements into a binary file format (MP4-SA) suitable for transmission and storage. MP4-SA is different from standards like the MIDI File Format, because it includes not only the notes to play, but the method for turning notes into sound. As a result, MP4-SA is normative -- an MP4-SA file will sound identical when converted by any compliant decoder. If the instrument models use algorithmic synthesis instead of wavetables, an MP4-SA file can describe realistic musical performances without using any audio data -- just score data, mixdown cues, and DSP algorithms. In this case, the MP4-SA file is about the same size as a MIDI File, but is a lossless encoding of the audio heard at mixdown. Just like a WAV file -- but 50 to 1000 times smaller! An ExampleThis example shows how to create audio content in MPEG-4 Structured Audio. It shows a SAOL and a SASL program that generates a tone burst sound. Audio output for the example was created using sfront, a translator that converts MP4-SA files into efficient C programs that generate audio. |
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