redsea is a lightweight command-line FM-RDS decoder that supports many RDS features.
It prints newline-delimited JSON where
each line corresponds to one RDS group. It can also print "raw" undecoded hex blocks (--output hex).
Please refer to the wiki for input data formats.
Redsea is compatible with the RTL-SDR USB radio stick via the
rtl_fm tool, and any other SDR via a tool like csdr (see wiki). It can decode MPX from
raw PCM or audio files, ASCII bitstreams, the hex format used by RDS Spy, or the TEF6686 serial format.
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}Redsea needs to be built from source, but this is not very complicated. Commands are provided
below (you can skip the $ at the start of each command).
On Ubuntu:
$ sudo apt install git build-essential meson libsndfile1-dev libliquid-dev
Or on older Debians:
$ sudo apt-get install python3-pip ninja-build build-essential libsndfile1-dev libliquid-dev nlohmann-json3-dev
$ pip3 install --user meson
Or on macOS using Homebrew:
$ brew install meson libsndfile liquid-dsp nlohmann-json
$ xcode-select --install
Meson will later download nlohmann-json for you if it can't be found in the package repositories.
It's also possible to build redsea on Windows, either in Cygwin or by building an .exe with MSYS2/MinGW. This is a bit more involved - instructions are in the wiki.
Downloading a release version is recommended.
Alternatively, if you wish to have the latest snapshot, you can also clone this git repository. The snapshot might be more work-in-progress than the releases, although we attempt to keep the main branch stable.
$ git clone https://github.com/windytan/redsea.git
$ cd redsea
$ meson setup build && cd build
$ meson compile
Now the binary executable is compiled and you can run it!
You can install the binary using meson install if you so wish. By default,
it will be installed under /usr/local, but this can be changed by providing
e.g. meson setup build --prefix /usr/local. See the
Meson guide
for more.
If you cloned the repository you can later get the latest updates and recompile:
$ git pull
$ cd build && meson compile
If your Linux system has very little RAM (e.g. Raspberry Pi), please use the below
line instead of meson compile to limit the number of build processes:
$ taskset -c 0 meson compile
The compilation will still require at least 500 MB of free RAM.
Redsea reads an MPX signal from stdin by default. It expects the input to be raw 16-bit signed-integer PCM.
Here's an example command that listens to 87.9 MHz using rtl_fm and displays
the RDS groups:
rtl_fm -M fm -l 0 -A std -p 0 -s 171k -g 20 -F 9 -f 87.9M | redsea -r 171kPlease refer to the wiki for more details and usage examples.
radio_command | redsea [OPTIONS]
redsea -f WAVEFILE
-b, --input-bits Same as --input bits (for backwards compatibility).
-c, --channels CHANS Number of channels in the raw input signal. Channels are
interleaved streams of samples that are demodulated
independently.
-e, --feed-through Echo the input signal to stdout and print decoded groups
to stderr. This only works for raw PCM.
-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 Read MPX input from a wave file with headers (.wav,
.flac, ...). If you have headered wave data via stdin,
use '-'. Or you can specify another format with --input.
-h, --input-hex Same as --input hex (for backwards compatibility).
-i, --input FORMAT Decode input as FORMAT (see the redsea wiki in github
for more info).
bits Unsynchronized ASCII bit stream (011010110...).
All characters but '0' and '1' are ignored.
hex RDS Spy hex format. (Timestamps will be ignored)
mpx MPX as raw mono S16LE PCM. Remember to also
specify --samplerate. If you're reading from a
sound file with headers (WAV, FLAC, ...) don't
specify this.
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.
--no-fec Disable forward error correction; always reject blocks
with incorrect syndromes. In noisy conditions, fewer errors
will slip through, but also fewer blocks in total; see wiki
for discussion.
-o, --output FORMAT Print output as FORMAT:
hex RDS Spy hex format.
json Newline-delimited JSON (default).
-p, --show-partial Under noisy conditions, redsea may not be able to fully
receive all information. Multi-group data such as PS
names, RadioText, and alternative frequencies are
especially vulnerable. This option makes it display them
even if not fully received, prefixed with partial_.
-r, --samplerate RATE Set sample frequency of raw PCM input in Hz. Will
resample if this differs from 171000 Hz.
-R, --show-raw Include 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 Same as --output hex (for backwards compatibility).
- Linux/macOS/Windows
- For realtime decoding, a Raspberry Pi 1 or faster
- libiconv 1.16
- libsndfile 1.0.31
- liquid-dsp release 1.3.2
- nlohmann-json
rtl_fm(from rtl-sdr) or any other source that can output demodulated FM multiplex signals
- Linux/macOS/Cygwin/MSYS2+MinGW
- C++14 compiler
- meson + ninja
- 500 MB of free memory for non-parallel build (breakdown)
- Catch2
If you've installed liquid-dsp yet meson 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
We welcome bug reports and documentation contributions. Or take a peek at our open issues to see where we could use a hand. 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 --output hex switch. You could use a
gist or an external pastebin service and post a link to it in our Github
Discussions.
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. (iconvpp has its own license.) See LICENSE.
Note: This software is not safety certified. Do not rely on it for emergency communication, accurate traffic / weather information, or life-critical situations.