FDK-AAC-DABplus

This is an open-source version of DAB+ encoder.

It has been extracted from the Android sources, and modified so as to support the 960 transform and the DAB+ framing.

fdk-aac-dabplus reads audio data from standard input, and outputs data on standard output. The second tool fdk-aac-dabplus-zmq outputs frames using ZeroMQ, which can be used with the inputZmq from ODR-DabMux

Installation

Prerequisites

fdk-aac-dabplus depends on libfec.

fdk-aac-dabplus-zmq depends on libfec and ZeroMQ.

For instructions on how to install these, please see ODR-DabMux#Prerequisites

Building

git clone https://github.com/mpbraendli/fdk-aac-dabplus.git
cd fdk-aac-dabplus
./bootstrap
./configure --enable-example --enable-zmq
make
sudo make install

Remove the flag --enable-zmq if you don't want to compile fdk-aac-dabplus-zmq

If the bootstrap step fails, you can try

autoreconf -i

instead.

Usage

Encoding

After successful installation, it can be used to encode DAB+ in several ways.

Encoding of audio input, output to fifo:

ALSASRC="default"
BITRATE=64

sox -t alsa $ALSASRC -b 16 -t raw - rate 48k channels 2 | \
  ../fdk-aac-dabplus/aac-enc-dabplus \
  -i /dev/stdin -b $BITRATE -f raw -a -o -o /dev/stdout 2>/dev/null | \
  mbuffer -q -m 10k -P 100 -s 360 > station1.fifo

Encoding of audio input, output to odr-dabmux using ZeroMQ

ALSASRC="default"
BITRATE=64
DST="tcp://your.dabmux.example.com:9000"

sox -t alsa $ALSASRC -b 16 -t raw - rate 48k channels 2 | \
  ../fdk-aac-dabplus/aac-enc-dabplus-zmq \
  -i /dev/stdin -b $BITRATE -f raw -a -o $DST

Live Stream enconding and preparing for DAB mux:

arecord -t raw -f S16_LE -c 2 -r 48000 -D plughw:CARD=Loopback,DEV=0,SUBDEV=0 | \
aac-enc-dabplus -b 24 -f raw -c 2 -r 48000 -i /dev/stdin -o /dev/stdout 2>/dev/null | \
mbuffer -q -m 10k -P 100 -s 360 > station1.fifo

Wave file enconding and preparing for odr-dabmux:

aac-enc-dabplus -a -b 64 -i wave_file.wav -o station1.dabp

Also have a look at the encode- scripts available in the [mmbtools-aux repository]

Problem solving

If you are using a pipe between the encoder and odr-dabmux, and you see a lot of errors like this:

<2> ERROR: Incomplete DAB+ frame! 136 != 360
<5> reach end of file -> rewinding
<2> ERROR: Can't rewind file
<6> ETI frame number: 228

Then the stream has to be buffered before giving it to muxer, this additional buffer installed between encoder and fifo. To calculate proper block size for mbuffer ("-s" parameter), the table below may be used:

DAB+ Stream bitrate, kbps	Block size, bytes
16	240
24	360
32	480
48	720
56	840
64	960
72	1080
128	1920
160	2400

In example above, for stream with bitrate 24 kbps, mbuffer size set to 360 bytes. This trick helping to solve problem.

In the case you are using ZeroMQ between the encoder and odr-dabmux, and you see errors that the size of the data is wrong, then the configured bitrate in the mux probably doesn't correspond to the bitrate given to the encoder. Make sure they are identical.