1 == Opus audio codec == 2 3 Opus 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 6 Voice over IP, videoconferencing, in-game chat, and even remote live music 7 performances. It can scale from low bit-rate narrowband speech to very high 8 quality stereo music. 9 10 Opus, when coupled with an appropriate container format, is also suitable 11 for non-realtime stored-file applications such as music distribution, game 12 soundtracks, portable music players, jukeboxes, and other applications that 13 have historically used high latency formats such as MP3, AAC, or Vorbis. 14 15 Opus is specified by IETF RFC 6716: 16 http://tools.ietf.org/html/rfc6716 17 18 The Opus format and this implementation of it are subject to the royalty- 19 free patent and copyright licenses specified in the file COPYING. 20 21 This package implements a shared library for encoding and decoding raw Opus 22 bitstreams. Raw Opus bitstreams should be used over RTP according to 23 http://tools.ietf.org/html/draft-spittka-payload-rtp-opus 24 25 The package also includes a number of test tools used for testing the 26 correct operation of the library. The bitstreams read/written by these 27 tools should not be used for Opus file distribution: They include 28 additional debugging data and cannot support seeking. 29 30 Opus stored in files should use the Ogg encapsulation for Opus which is 31 described at: 32 http://wiki.xiph.org/OggOpus 33 34 An opus-tools package is available which provides encoding and decoding of 35 Ogg encapsulated Opus files and includes a number of useful features. 36 37 Opus-tools can be found at: 38 https://git.xiph.org/?p=opus-tools.git 39 or on the main Opus website: 40 http://opus-codec.org/ 41 42 == Compiling libopus == 43 44 To build from a distribution tarball, you only need to do the following: 45 46 % ./configure 47 % make 48 49 To build from the git repository, the following steps are necessary: 50 51 1) Clone the repository: 52 53 % git clone git://git.opus-codec.org/opus.git 54 % cd opus 55 56 2) Compiling the source 57 58 % ./autogen.sh 59 % ./configure 60 % make 61 62 3) Install the codec libraries (optional) 63 64 % sudo make install 65 66 Once you have compiled the codec, there will be a opus_demo executable 67 in the top directory. 68 69 Usage: 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 74 mode: voip | audio | restricted-lowdelay 75 options: 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 95 input and output are little-endian signed 16-bit PCM files or opus 96 bitstreams with simple opus_demo proprietary framing. 97 98 == Testing == 99 100 This package includes a collection of automated unit and system tests 101 which SHOULD be run after compiling the package especially the first 102 time it is run on a new platform. 103 104 To run the integrated tests: 105 % make check 106 107 There is also collection of standard test vectors which are not 108 included in this package for size reasons but can be obtained from: 109 http://opus-codec.org/testvectors/opus_testvectors.tar.gz 110 111 To run compare the code to these test vectors: 112 113 % curl -O http://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 == 118 119 This implementation uses floating-point by default but can be compiled to 120 use only fixed-point arithmetic by setting --enable-fixed-point (if using 121 autoconf) or by defining the FIXED_POINT macro (if building manually). 122 The fixed point implementation has somewhat lower audio quality and is 123 slower on platforms with fast FPUs, it is normally only used in embedded 124 environments. 125 126 The implementation can be compiled with either a C89 or a C99 compiler. 127 While it does not rely on any _undefined behavior_ as defined by C89 or 128 C99, it relies on common _implementation-defined behavior_ for two's 129 complement architectures: 130 131 o 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)), 134 135 o For conversion to a signed integer of N bits, the value is reduced 136 modulo 2^N to be within range of the type, 137 138 o The result of integer division of a negative value is truncated 139 towards zero, and 140 141 o The compiler provides a 64-bit integer type (a C99 requirement 142 which is supported by most C89 compilers). 143
