redsea is a lightweight command-line FM-RDS decoder for Linux/macOS. It
supports a large [subset of RDS features][Wiki: Features].

[![release](https://img.shields.io/github/release/windytan/redsea.svg)](https://github.com/windytan/redsea/releases/latest)
![build](https://github.com/windytan/redsea/workflows/build/badge.svg)

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][Wiki: Input].

Redsea can be used with any [RTL-SDR][About 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][Wiki: Use cases].

[About RTL-SDR]: http://www.rtl-sdr.com/about-rtl-sdr
[Wiki: Features]: https://github.com/windytan/redsea/wiki/Supported-RDS-features
[Wiki: Input]: https://github.com/windytan/redsea/wiki/Input-formats

Example output:

```json
{"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}
```

## Contents

  * [Installation](#installation)
  * [Usage](#usage)
    * [Full usage](#full-usage)
    * [Formatting and filtering the JSON output](#formatting-and-filtering-the-json-output)
  * [Requirements](#requirements)
  * [Troubleshooting](#troubleshooting)
    * [Can't find liquid-dsp on macOS](#cant-find-liquid-dsp-on-macos)
    * [Can't find liquid-dsp on Linux](#cant-find-liquid-dsp-on-linux)
  * [Contributing](#contributing)
  * [Licensing](#licensing)

## Installation

These commands should be run in the terminal. Don't type the `$` in the
beginning.

1. 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

2. Clone the repository (unless you downloaded a release zip file):

        $ git clone https://github.com/windytan/redsea.git
        $ cd redsea

3. Compile redsea:

        $ ./autogen.sh && ./configure && make

4. 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`).

[liquid-dsp]: https://github.com/jgaeddert/liquid-dsp/releases/tag/v1.3.2

## Usage

By default, a 171 kHz single-channel 16-bit MPX signal is expected via stdin.

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][Wiki: Use cases] for more details and usage examples.

[Wiki: Use cases]: https://github.com/windytan/redsea/wiki/Use-cases


### Full usage

```
radio_command | redsea [OPTIONS]
redsea -f WAVFILE

-b, --input-bits       Input is an unsynchronized ASCII bit stream
                       (011010110...). All characters but '0' and '1'
                       are ignored.

-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.

-h, --input-hex        The input is in the RDS Spy hex format.

-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 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.
```

### Formatting and filtering the 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'


## Requirements

* 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][liquid-dsp] release 1.3.2
* `rtl_fm` (from [rtl-sdr](http://sdr.osmocom.org/trac/wiki/rtl-sdr)) or any
   other source that can output demodulated FM multiplex signals

## Troubleshooting

### Can't find liquid-dsp on macOS

If you've installed [liquid-dsp][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

### Can't find liquid-dsp on Linux

Try running this in the terminal:

    sudo ldconfig

## Contributing

Bug reports are welcome. See [CONTRIBUTING](CONTRIBUTING.md) 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.

## Licensing

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.
