feat: add a GStreamer runner to launch pipelines

[ylatuya]

Add a new GStreamer runner to launch pipelines that gives use more control in errors and allow us to differentiate for example between a pipelines miss-configuration or a format that's not supported.

This a first iteration in order to support #319

[dabrain34]

I would put the gstreamer cffi in decoders as it should be not located in fluster base. IMHO fluster is GStreamer agnostic.

[ylatuya]

I would put the gstreamer cffi in decoders as it should not be located in the fluster base. IMHO, fluster is GStreamer agnostic.

The fluster.gstreamer namespace contains generic helpers around GStreamer that are not specific to decoders, that's why I decided to leave them under fluster.gstreamer instead of fluster.decoders.gstreamer. They can be used by a GStreamer decoder or a future GStreamer encoder.

[rsanchez87]

An important thing I'm seeing is that in l51 of pyproject.toml, it would be necessary to add fluster.gstreamer to the package list:

packages = ["fluster", "fluster.decoders", "fluster.gstreamer"]

cc: @ylatuya

[rsanchez87]

Something to keep in mind... now that #319 uses exit code 69 for "not supported" (matching the gst-launch upstream change), the runner here should return 69 also instead of INIT_ERROR = 2 for unsupported formats.

Otherwise the NotSupportedError path in utils.py will not be activated, since it only checks 69

[ylatuya]

@dabrain34 I have rebased this MR on top of your work.

The runner is now returning a new NOT_SUPPORTED exit code when a missing-plugin or missing-codec error is emitted in the bus. The decoder implementation will raise a NotSupported exception in that scenario, allowing for test results to be reported correctly.

[rsanchez87]

Can you add something like:

NOT_SUPPORTED (4) - Format/codec not supported

[rsanchez87]

Can you add something like:

4 - Format/codec not supported