Definition of terms used in the present document, can be found in TS 26.445, TS 26.451, TS 26.449, TS 26.450, TS 26.447, TS 26.448 and TS 26.446.

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905. ACELP AMR-WB CNG DTX EVS FB FEC IP JBM MSB MTSI NB PS PSTN SAD SC-VBR SID SWB VAD WB WMOPS

This clause gives an overview of the structure of the bit-exact C code and provides an overview of the contents and organization of the C code attached to the present document. The C code has been verified on the following systems:

• IBM PC compatible computers with Windows 7 or 8 operating system and Microsoft Visual C++ 2017 compiler, 32 bit builds.
• IBM PC compatible computers with Linux operating system and GNU gcc compiler version 4.3.x, 32 bit builds.
  ANSI-C was selected as the programming language because portability was desirable.

The C code distribution is organized as follows:

The distributed files with suffix "c" contain the source code and the files with suffix "h" are the header files. The ROM data is contained in files named "rom_xxx" with suffix "c". Makefiles are provided for the platforms in which the C code has been verified (listed above). Once the software is installed, this directory will have a compiled version of the encoder (named EVS_cod) and the decoder (named EVS_dec).

The codec for Enhanced Voice Services is implemented in two programs:

• EVS_cod: speech/audio encoder;
• EVS_dec: speech/audio decoder.

The programs should be called like:

• EVS_cod [encoder options] <speech/audio input file> <parameter file>;
• EVS_dec [decoder options]<parameter file> <speech/audio output file>.

The speech/audio files contain 16-bit linear encoded PCM speech/audio samples and the parameter files contain encoded speech/audio data. The encoder and decoder options will be explained by running the applications without input arguments. See the file readme.txt for more information on how to run the encoder and decoder programs.

This clause describes the file formats used by the encoder and decoder programs. The test sequences defined in TS 26.444 also use the file formats described here.

Speech files read by the encoder and written by the decoder consist of 16-bit words speech/audio sample. The byte order depends on the host architecture (e.g. LSByte first on PCs, etc.). Both the encoder and the decoder program process complete frames (corresponding to 20 ms, for example, 640 samples at 32 kHz sampling frequency) only. The encoder will pad the last frame to integer multiples of 20ms frames, i.e. n speech frames will be produced from an input file with a length between [(n-1)*20ms+1 sample; n*20ms]. The files produced by the decoder will always have a length of n*20ms.

The encoder program can optionally read in a rate switching profile which specifies the encoding bitrate for each frame of speech processed. The file is a binary file, generated by 'gen-rate-profile', which is part of STL 2009, as contained in ITU-T G.191 [11]. The rate switching profile can contain EVS primary mode bitrates and AMR-WB IO mode bitrates arbitrarily. I.e. switching between the two modes can be specified by the rate switching profile.

 

  The fields have the following size and meaning:

• Packet size: 32 bit unsigned integer. (= 12 + 2 + DATA_LENGTH)
• Arrival time: 32 bit unsigned integer. in ms.
• RTP header: 96 bits (see RFC 3550), including RTP timestamp and SSRC.

The encoder program can optionally read in a bandwidth switching profile, which specifies the encoding bandwidth for each frame of speech processed. The file is a text file where each line contains "nb_frames B". B specifies the signal bandwidth that is one of the supported four bandwidths, i.e. NB, WB, SWB or FB. And "nb_frames" is an integer number of frames and specifies the duration of activation of the accompanied signal bandwidth B.

The encoder program can optionally read in a configuration file which specifies the values of FEC indicator p and FEC offset o, where FEC indicator, p: LO or HI, and FEC offset, o: 2, 3, 5, or 7 in number of frames. Each line of the configuration file contains the values of p and o separated by a space. The channel-aware configuration file is meant to simulate channel feedback from a receiver to a sender, i.e. the decoder would generate FEC indication and FEC offset values for receiver feedback that correspond to the current transmission channel characteristics, thereby allowing optimization of the transmission by the encoder which applies the FEC offset and FEC indication when in the channel-aware mode.

The decoder can generate a JBM trace file with the -Tracefile switch as a by-product of the decoder operation in case of JBM operation (which is triggered with the -VOIP switch on the decoder side). The trace file is a CSV file with semi-colon as separator. The trace file starts with one header line that contains the column names in the following order: rtpSeqNo;rtpTs;rcvTime;playtime;active For each played out speech frame one entry is written to the trace file. The interval of the playtime values is usually 20ms, but may differ, depending on the JBM operation. Each entry is a line in the trace file that contains values as specified in Table 2.