1== Opus audio codec == 2 3Opus is a codec for interactive speech and audio transmission over the Internet. 4 5 Opus can handle a wide range of interactive audio applications, including 6Voice over IP, videoconferencing, in-game chat, and even remote live music 7performances. It can scale from low bit-rate narrowband speech to very high 8quality stereo music. 9 10 Opus, when coupled with an appropriate container format, is also suitable 11for non-realtime stored-file applications such as music distribution, game 12soundtracks, portable music players, jukeboxes, and other applications that 13have historically used high latency formats such as MP3, AAC, or Vorbis. 14 15 Opus is specified by IETF RFC 6716: 16 https://tools.ietf.org/html/rfc6716 17 18 The Opus format and this implementation of it are subject to the royalty- 19free patent and copyright licenses specified in the file COPYING. 20 21This package implements a shared library for encoding and decoding raw Opus 22bitstreams. Raw Opus bitstreams should be used over RTP according to 23 https://tools.ietf.org/html/rfc7587 24 25The package also includes a number of test tools used for testing the 26correct operation of the library. The bitstreams read/written by these 27tools should not be used for Opus file distribution: They include 28additional debugging data and cannot support seeking. 29 30Opus stored in files should use the Ogg encapsulation for Opus which is 31described at: 32 https://wiki.xiph.org/OggOpus 33 34An opus-tools package is available which provides encoding and decoding of 35Ogg encapsulated Opus files and includes a number of useful features. 36 37Opus-tools can be found at: 38 https://git.xiph.org/?p=opus-tools.git 39or on the main Opus website: 40 https://opus-codec.org/ 41 42== Compiling libopus == 43 44To build from a distribution tarball, you only need to do the following: 45 46% ./configure 47% make 48 49To build from the git repository, the following steps are necessary: 50 511) Clone the repository: 52 53% git clone https://git.xiph.org/opus.git 54% cd opus 55 562) Compiling the source 57 58% ./autogen.sh 59% ./configure 60% make 61 623) Install the codec libraries (optional) 63 64% sudo make install 65 66Once you have compiled the codec, there will be a opus_demo executable 67in the top directory. 68 69Usage: opus_demo [-e] <application> <sampling rate (Hz)> <channels (1/2)> 70 <bits per second> [options] <input> <output> 71 opus_demo -d <sampling rate (Hz)> <channels (1/2)> [options] 72 <input> <output> 73 74mode: voip | audio | restricted-lowdelay 75options: 76 -e : only runs the encoder (output the bit-stream) 77 -d : only runs the decoder (reads the bit-stream as input) 78 -cbr : enable constant bitrate; default: variable bitrate 79 -cvbr : enable constrained variable bitrate; default: 80 unconstrained 81 -bandwidth <NB|MB|WB|SWB|FB> 82 : audio bandwidth (from narrowband to fullband); 83 default: sampling rate 84 -framesize <2.5|5|10|20|40|60> 85 : frame size in ms; default: 20 86 -max_payload <bytes> 87 : maximum payload size in bytes, default: 1024 88 -complexity <comp> 89 : complexity, 0 (lowest) ... 10 (highest); default: 10 90 -inbandfec : enable SILK inband FEC 91 -forcemono : force mono encoding, even for stereo input 92 -dtx : enable SILK DTX 93 -loss <perc> : simulate packet loss, in percent (0-100); default: 0 94 95input and output are little-endian signed 16-bit PCM files or opus 96bitstreams with simple opus_demo proprietary framing. 97 98== Testing == 99 100This package includes a collection of automated unit and system tests 101which SHOULD be run after compiling the package especially the first 102time it is run on a new platform. 103 104To run the integrated tests: 105% make check 106 107There is also collection of standard test vectors which are not 108included in this package for size reasons but can be obtained from: 109https://opus-codec.org/testvectors/opus_testvectors.tar.gz 110 111To run compare the code to these test vectors: 112 113% curl -O https://opus-codec.org/testvectors/opus_testvectors.tar.gz 114% tar -zxf opus_testvectors.tar.gz 115% ./tests/run_vectors.sh ./ opus_testvectors 48000 116 117== Portability notes == 118 119This implementation uses floating-point by default but can be compiled to 120use only fixed-point arithmetic by setting --enable-fixed-point (if using 121autoconf) or by defining the FIXED_POINT macro (if building manually). 122The fixed point implementation has somewhat lower audio quality and is 123slower on platforms with fast FPUs, it is normally only used in embedded 124environments. 125 126The implementation can be compiled with either a C89 or a C99 compiler. 127While it does not rely on any _undefined behavior_ as defined by C89 or 128C99, it relies on common _implementation-defined behavior_ for two's 129complement architectures: 130 131o Right shifts of negative values are consistent with two's 132 complement arithmetic, so that a>>b is equivalent to 133 floor(a/(2^b)), 134 135o For conversion to a signed integer of N bits, the value is reduced 136 modulo 2^N to be within range of the type, 137 138o The result of integer division of a negative value is truncated 139 towards zero, and 140 141o The compiler provides a 64-bit integer type (a C99 requirement 142 which is supported by most C89 compilers). 143