After almost 6 months, a new release of the GStreamer Rust bindings and the GStreamer plugin writing infrastructure for Rust is out. As usual this was coinciding with the release of all the gtk-rs crates to make use of all the new features they contain.
Thanks to all the contributors of both gtk-rs and the GStreamer bindings for all the nice changes that happened over the last 6 months!
And as usual, if you find any bugs please report them and if you have any questions let me know.
GStreamer Bindings
For the full changelog check here.
Most changes this time were internally, especially because many user-facing changes (like Debug impls for various types) were already backported to the minor releases in the 0.11 release series.
WebRTC
The biggest change this time is probably the inclusion of bindings for the GStreamer WebRTC library.
This allows using building all kinds of WebRTC applications outside the browser (or providing a WebRTC implementation for a browser), and while not as full-featured as Google’s own implementation, this interoperates well with the various browsers and generally works much better on embedded devices.
A small example application in Rust is available here.
Serde
Optionally, serde trait implementations for the Serialize and Deserialize trait can be enabled for various fundamental GStreamer types, including caps, buffers, events, messages and tag lists. This allows serializing them into any format that can be handled by serde (which are many!), and deserializing them back to normal Rust structs.
Generic Tag API
Previously only a strongly-typed tag API was exposed that made it impossible to use the wrong data type for a specific tag, e.g. code that tries to store a string for the track number or an integer for the title would simply not compile:
let mut tags = gst::TagList::new();
{
let tags = tags.get_mut().unwrap();
tags.add::<Title>(&"some title", gst::TagMergeMode::Append);
tags.add::<TrackNumber>(&12, gst::TagMergeMode::Append);
}
While this is convenient, it made it rather complicated to work with tag lists if you only wanted to handle them in a generic way. For example by iterating over the tag list and simply checking what kind of tags are available. To solve that, a new generic API was added in addition. This works on glib::Values, which can store any kind of type, and using the wrong type for a specific tag would simply cause an error at runtime instead of compile-time.
let mut tags = gst::TagList::new();
{
let tags = tags.get_mut().unwrap();
tags.add_generic(&gst::tags::TAG_TITLE, &"some title", gst::TagMergeMode::Append)
.expect("wrong type for title tag");
tags.add_generic(&gst::tags::TAG_TRACK_NUMBER, &12, gst::TagMergeMode::Append)
.expect("wrong type for track number tag");
}
This also greatly simplified the serde serialization/deserialization for tag lists.
GStreamer Plugins
For the full changelog check here.
gobject-subclass
The main change this time is that all the generic GObject subclassing infrastructure was moved out of the gst-plugin crate and moved to its own gobject-subclass crate as part of the gtk-rs organization.
As part of this, some major refactoring has happened that allows subclassing more different types but also makes it simpler to add new types. There are also experimental crates for adding some subclassing support to gio and gtk, and a PR for autogenerating part of the code via the gir code generator.
More classes!
The other big addition this time is that it’s now possible to subclass GStreamer Pads and GhostPads, to implement the ChildProxy interface and to subclass the Aggregator and AggregatorPad class.
This now allows to write custom mixer/muxer-style elements (or generally elements that have multiple sink pads) in Rust via the Aggregator base class, and to have custom pad types for elements to allow for setting custom properties on the pads (e.g. to control the opacity of a single video mixer input).
There is currently no example for such an element, but I’ll add a very simple video mixer to the repository some time in the next weeks and will also write a blog post about it for explaining all the steps.