redsea is a lightweight command-line FM-RDS decoder for Linux/macOS. It supports a large subset of RDS features.
Decoded RDS groups are printed to the terminal as line-delimited JSON objects
or, optionally, undecoded hex blocks (-x). Please refer to the wiki for
input data formats.
Redsea can be used with any RTL-SDR USB radio stick with the
rtl_fm tool, or any other SDR via csdr, for example. It can also
decode raw ASCII bitstream, the hex format used by RDS Spy, and audio files
containing multiplex signals (MPX). These use cases are documented in
the wiki.
Example output:
{"pi":"0xD3C2","group":"0A","ps":"MDR JUMP","di":{"dynamic_pty":true},"is_music":true,"prog_type":"Pop music","ta":false,"tp":false}
{"pi":"0xD3C2","group":"2A","prog_type":"Pop music","tp":false}
{"pi":"0xD3C2","group":"2A","radiotext":"Das Leichteste der Welt von Silbermond JETZT AUF MDR JUMP","prog_type":"Pop music","tp":false}
{"pi":"0xD3C2","group":"12A","prog_type":"Pop music","radiotext_plus":{"item_running":true,"item_toggle":1,"tags":[{"content-type":"item.title","data":"Das Leichteste der Welt"},{"content-type":"item.artist","data":"Silbermond"}]},"tp":false}
{"pi":"0xD3C2","group":"3A","open_data_app":{"app_name":"RadioText+ (RT+)","oda_group":"12A"},"prog_type":"Pop music","tp":false}These commands should be run in the terminal. Don't type the $ in the
beginning.
-
Install the prerequisites. On Ubuntu:
$ sudo apt install git build-essential autoconf libsndfile1-dev libliquid-dev
Or on macOS (OSX) using Homebrew:
$ brew install autoconf automake libsndfile liquid-dsp
$ xcode-select --install
-
Clone the repository (unless you downloaded a release zip file):
$ git clone https://github.com/windytan/redsea.git $ cd redsea -
Compile redsea:
$ ./autogen.sh && ./configure && make -
Install:
$ make install
How to later get the latest updates and recompile:
$ git pull
$ ./autogen.sh && ./configure && make clean && make
$ make install
For a slower machine it can take some time to compile the TMC support. This can
be disabled (./configure --disable-tmc).
If you only need to decode hex or binary input and don't need demodulation,
you can compile redsea without liquid-dsp (./configure --without-liquid).
By default, an MPX signal is expected via stdin (raw 16-bit signed-integer PCM sampled at 171 kHz).
The simplest way to view RDS groups using rtl_fm is:
rtl_fm -M fm -l 0 -A std -p 0 -s 171k -g 20 -F 9 -f 87.9M | redsea
Please refer to the wiki for more details and usage examples.
radio_command | redsea [OPTIONS]
redsea -f WAVEFILE
-c, --channels CHANS Number of channels in the raw input signal. Each
channel is demodulated independently.
-e, --feed-through Echo the input signal to stdout and print
decoded groups to stderr.
-E, --bler Display the average block error rate, or the
percentage of blocks that had errors before
error correction. Averaged over the last 12
groups. For hex input, this is the percentage
of missing blocks.
-f, --file FILENAME Use an audio file as MPX input. All formats
readable by libsndfile should work.
-i, --input FORMAT Decode stdin as FORMAT (see the wiki for more info):
bits Unsynchronized ASCII bit stream (011010110...).
All characters but '0' and '1' are ignored.
hex RDS Spy hex format.
mpx Mono S16LE PCM-encoded MPX waveform (default).
tef Serial data from the TEF6686 tuner.
-l, --loctable DIR Load TMC location table from a directory in TMC
Exchange format. This option can be specified
multiple times to load several location tables.
-p, --show-partial Show some multi-group data even before they've been
fully received (PS names, RadioText, alternative
frequencies). partial_ will be prepended to their
names. This is good for noisy conditions.
-r, --samplerate RATE Set sample frequency of the raw MPX input signal in Hz.
Will resample (slow) if this differs from 171000 Hz.
-R, --show-raw Show raw group data as hex in the JSON stream.
-t, --timestamp FORMAT Add time of decoding to JSON groups; see
man strftime for formatting options (or
try "%c"). Use "%f" to add hundredths of seconds.
-u, --rbds RBDS mode; use North American program type names
and "back-calculate" the station's call sign from
its PI code. Note that this calculation gives an
incorrect call sign for most stations that transmit
TMC.
-v, --version Print version string and exit.
-x, --output-hex Output hex groups in the RDS Spy format,
suppressing JSON output.
The JSON output can be tidied and/or colored using jq:
$ rtl_fm ... | redsea | jq
It can also be used to extract only certain fields, for instance the program type:
$ rtl_fm ... | redsea | jq '.prog_type'
- Linux or macOS
- For realtime decoding, a Raspberry Pi 1 or faster
- ~8 MB of free memory (~128 MB for RDS-TMC)
- C++14 compiler
- GNU autotools
- libiconv 1.16
- libsndfile 1.0.31
- liquid-dsp release 1.3.2
rtl_fm(from rtl-sdr) or any other source that can output demodulated FM multiplex signals
If you've installed liquid-dsp yet configure can't find it, it's
possible that XCode command line tools aren't installed. Run this command to fix
it:
xcode-select --install
Try running this in the terminal:
sudo ldconfig
Bug reports are welcome. See CONTRIBUTING for more information.
Also, if a station in your area is transmitting an interesting RDS feature
that should be implemented in redsea, I would be happy to see a minute or
two's worth of hex data using the -x switch. You could use a gist or an
external pastebin service and post a link to it.
Redsea is released under the MIT license, which means it is copyrighted to Oona Räisänen OH2EIQ yet you're free to use it provided that the copyright information is not removed. (jsoncpp and iconvpp have their own licenses.) See LICENSE.
This software should never be relied on for emergency communication, accurate traffic / weather information, or when your life is on the line.