Allow recording IQ samples in the SigMF format

[Niautanor]

This implements part 1 of #988. Users can choose between the old format (raw) and SigMF with a chooser in the iq tool window.

Since SigMF keeps metadata and signal data separate, the actual recording remains unchanged regardless of which format is selected (except for the file name). For this reason, .sigmf-data files are made available for playback in the iq tool as well (this does not work in the general case (yet) but .raw isn't super well defined either).

One potential improvement would be to do some refactoring to separate formats into different classes that can be interacted with during the recording. This would 1. more cleanly separate the code paths for raw and sigmf recordings and 2. allow adding more metadata during the recording (e.g. we could start a new capture object when we tune the radio to a different frequency or change the gain).

[vladisslav2011]

Hello.
Build log:

$ make -j33
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/home/vlad/warez/gqrx-my/src/applications/gqrx/mainwindow.cpp: In member function 'void MainWindow::startIqRecording(const QString&, const QString&)':
/home/vlad/warez/gqrx-my/src/applications/gqrx/mainwindow.cpp:1557:61: error: 'QFile::QFile(const QFile&)' is private within this context
     auto metaFile = QFile(filenameTemplate.arg("sigmf-meta"));
                                                             ^
In file included from /usr/include/x86_64-linux-gnu/qt5/QtCore/qnamespace.h:43:0,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs.h:48,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:46,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qsettings.h:43,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/QSettings:1,
                 from /home/vlad/warez/gqrx-my/src/applications/gqrx/mainwindow.cpp:28:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qfile.h:149:5: note: declared private here
     Q_DISABLE_COPY(QFile)
     ^
/home/vlad/warez/gqrx-my/src/applications/gqrx/mainwindow.cpp:1557:61: error: use of deleted function 'QFile::QFile(const QFile&)'
     auto metaFile = QFile(filenameTemplate.arg("sigmf-meta"));
                                                             ^
In file included from /usr/include/x86_64-linux-gnu/qt5/QtCore/qnamespace.h:43:0,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs.h:48,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:46,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qsettings.h:43,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/QSettings:1,
                 from /home/vlad/warez/gqrx-my/src/applications/gqrx/mainwindow.cpp:28:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qfile.h:149:5: note: declared here
     Q_DISABLE_COPY(QFile)
     ^
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[Niautanor]

Huh. It built fine on my Arch machine but I just tested it again on Ubuntu and was able to reproduce that issue.

I think this might be because Arch defaults to C++17 (where X a = X() is not a copy) and Ubuntu defaults to C++14 (where it is). If that is the issue then it should be easy to fix.

[Niautanor]

That issue should be fixed with the new commit.

[vladisslav2011]

Confirmed. It builds and writes .sigmf-meta file.
The next step may by reading sample rate/center frequency from .sigmf-meta on file selection.

[argilo]

Thanks for this, and sorry for the long delay in looking at it. I'm starting to have a peek now. I'd love to see at least partial SigMF support in the next Gqrx release.

[Niautanor]

Thank you for having a look. Let me know if there is anything else that I can do for this. I took this as far as I needed for my use case at the time but I'm happy to do more work on this if there is interest.

[argilo]

It might be nice to store the device name and/or device string in the core:hw field. I'm not sure it's easy to get at though, so it would be fine to leave that for a future PR.

[argilo]

I merged the suggestions, rebased, and updated the news & contributors list. I'll merge once CI is happy.

[argilo]

A couple more things we could potentially include in sigmf-meta:

• capture_details:gain
  • could be retrieved with receiver::get_gain_names followed by summing the values of receiver::get_gain
  • would only be correct if gain is not adjusted during the recording, but this should be the case in most recordings
• capture_details:acquisition_bandwidth
  • could be retrieved with receiver::get_analog_bandwidth