For SDPMessageRef, StructureRef and CapsFeatureRef this involves the
conversion from and to a glib::Value. Specifically this means that e.g.
a StructureRef can be retrieved from a glib::Value via borrowing, i.e.
without creating a copy of the structure first.
For all mini objects only retrieval from a glib::Value is implemented as
the other direction would allow to get multiple immutable references
from a mutable reference without borrowing, which is not allowed and
would make it possible to observe a mini object changing while having an
immutable reference to it.
This makes usage of RLS/rust-analyzer on the repository much faster and
less annoying as the docs don't have to be included and removed on every
change.
This applies to the ones of the appsink, appsrc and bus. If we would
store a strong reference then they would keep alive the underlying
object forever even if their pipeline disappeared in the meantime.
Like this e.g. the bus stream would start returning None once the bus
was destroyed, similar to how other channels are working in Rust.
The 'failure' crate has been stale for quite some time and better
alternatives has been developed since its introduction. We choose the
'anyhow' and 'derive_more' to replace it.
This code rework the examples to use the new 2018 edition and also
rework the code to avoid using unnecessary 'extern crate' calls.
The 'use extern crate gstreamer as gst', as well as the other gstramer
related crates, were kept, otherwise we'd need to do it on 'Cargo.toml'
but it would make it more difficult to figure out the respective crate
name.
At the moment we are building 3 independent images, each one having a different
Rust version. This works perfectly fine but we can save storage space and
bandwith by making a smarter use of Docker's layering system.
Introducing a new 'base' image containing all the deps, including
GStreamer, acting as a base for the actual images.
As a result most of the actual content is now shared accross the same
Docker layer. This would save us from downloading/building all the deps
when updating images and will reduce storage and transfers for runners.
