This is an implementation of 3GPP TS 26.445 Annex A. Sometimes, 3GPP Enhanced Voice Services (EVS) are called Full-HD Voice. Qualcomm calls it Ultra HD Voice. Research papers comparing EVS with other audio codecs were published at ICASSP 2015. Further examples…
To add a codec for SIP/SDP (m=, rtmap, and ftmp), you create a format module in Asterisk: codec_evs.patch (for m= and rtmap) and res/res_format_attr_evs.c (for fmtp). However, this requires both call legs to support EVS (pass-through only). If one leg does not support EVS, the call has no audio. Or, if you use the pre-recorded voice and music files of Asterisk, these files cannot be heard, because they are not in EVS but in slin. Therefore, this repository adds not just a format module for the audio-codec EVS but a transcoding module as well: build_evs.patch and codecs/codec_evs.c.
At least Asterisk 13.7 is required. These changes were last tested with Asterisk 13.13 (and Asterisk 14.2). If you use a newer version and the patch fails, please, report!
cd /usr/src/
wget downloads.asterisk.org/pub/telephony/asterisk/asterisk-13-current.tar.gz
tar zxf ./asterisk*
cd ./asterisk*
sudo apt-get --assume-yes install build-essential autoconf libssl-dev libncurses-dev libnewt-dev libxml2-dev libsqlite3-dev uuid-dev libjansson-dev libblocksruntime-dev xmlstarlet
Apply the patch:
wget github.com/traud/asterisk-evs/archive/master.zip
unzip -qq master.zip
rm master.zip
cp --verbose --recursive ./asterisk-evs*/* ./
patch -p0 <./codec_evs.patch
Install libraries:
If you do not want transcoding but pass-through only (because of license issues) please, skip this step. To support transcoding, you’ll need to install the 3GPP EVS Reference Implementation, for example in Debian/Ubuntu:
wget www.etsi.org/deliver/etsi_ts/126400_126499/126443/14.00.00_60/ts_126443v140000p0.zip
unzip -qq ts_126443v*.zip
unzip -qq 26443-*-ANSI-C_source_code.zip
cd ./c-code
chmod +r ./lib_*/*.h
sudo mkdir /usr/include/3gpp-evs
sudo cp --verbose --target-directory=/usr/include/3gpp-evs ./lib_*/*.h
DEBUG=0 RELEASE=1 CFLAGS='-DNDEBUG -fPIC' make
cd ./build
rm ./decoder.o
gcc -shared -o lib3gpp-evs.so *.o
sudo cp ./lib3gpp-evs.so /usr/lib/
cd /usr/src/asterisk*
patch -p0 <./build_evs.patch
patch -p0 <./force_limitations.patch
Run the bootstrap script to re-generate configure:
./bootstrap.sh
Configure your patched Asterisk:
./configure
Enable slin16 in menuselect for transcoding, for example via:
make menuselect.makeopts
./menuselect/menuselect --enable-category MENUSELECT_CORE_SOUNDS
Compile and install:
make
sudo make install
Currently, I am not aware of any other VoIP/SIP project offering EVS. Consequently, you have to patch two Asterisk servers and run EVS between those. My main objective was to play around, test, and learn more about EVS.
Although the Qualcomm Snapdragon 820 (and newer) chipset(s) offer EVS, not all phones come with EVS enabled. Of the remaining phones, not all offer the built-in VoIP/SIP client of the Android Open Source Platform (AOSP). Finally, I am not aware of one phone which bridges its EVS capabilities between the hardware chipset and that software client.
The Rohde & Schwarz CMW500 can be extended for EVS – however here, this transcoding module was not tested with that either.
Although this list is rather long, these features are disabled at SDP negotiation via the force_limitations.patch and should not create an interoperability issue.
- Compound payload: Several frames per payload, for example when FEC or a packetization time (ptime) longer than 20 ms are used. This is useful to lower the overall overhead (RTP, UDP, and IP).
- Packet-Loss Concealment (native PLC), see ASTERISK-25629…
- Channel Awareness (RTCP interaction), see ASTERISK-26584…
- Compact Format mode; not sure if that is possible with Asterisk, see
codec_evs.c:evs_sample_counter - AMR-WB IO without transcoding
The transcoding module works for me and contains everything I need. If you cannot code yourself, however, a feature is missing for you, please, report and send me at least a testing device.
everyone who made the 3GPP EVS Reference Implementation possible.