We want to enable passthrough internally, and only notify that
internally it has been enabled once the transcriber has been unlinked.
This way applications connected to the notify handler can synchronously
update the properties and attempt to disable passthrough again.
Doing so properly requires a refactoring of the transition to the
passthrough state, with the currently set passthrough mode maintained
separately from the target passthrough state.
This commit also finishes the work left incomplete in
17d7997137 by moving the passthrough
property to the sink pad class, making each transcriber passthrough
state independent from the others.
Also adds an example to demonstrate the behavior
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1856>
This new element puts together some of the elements we've written
in recent times (awstranscriber, tttocea608, textwrap, cccombiner)
into a convenience high-level element.
The design of the element is AV in -> AV (+ CC metas) out.
The element exposes property to set and unset a "passthrough" mode,
during which the transcriber element's state is set to NULL but kept
in the bin, in order for the user to be able to set properties on
sub elements no matter what the current mode is, using the
GstChildProxy interface.
In addition, the element ensures that the latency it reports stays
fixed so that playback continues uninterrupted.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/528>
Up to now, tttocea608 supported text/utf8, and no interface to
control the positioning of closed captions apart from new lines
in the input text.
CEA 608 supports a larger set of features than that, such as
positioning CC precisely in its 32 x 15 grid, styling text,
switching from one mode to another, resetting the base row
in roll-up mode etc ..
A custom, JSON-based format is now supported by the element
(caps application/x-json, format=cea608), allowing users to
control those features in a pretty advanced manner.
A side effect of this is that the approach previously used
by the element to ensure frame-accurate CC display is now
untenable: where we knew before that an input buffer would
at most span 74 buffers and calculate a somewhat reasonable
latency based on that, this is no longer possible. Instead
we pick the approach most CC encoders seem to pick, and
accept a certain latency at display time: for example the
flipping of the back buffer to the display buffer for a
10-character text buffer will occur 7 frames after its
PTS. This has obvious benefits in terms of code complexity
and should generally be acceptable.
+ Removes a now irrelevant test, updates other tests
+ Extracts the Mode enum to the root of the crate, it will
be used by another element in a follow-up commit
cargo-c will produce a pkg-config file making it easier to statically
link plugins.
Also add 'static' features for plugins depending on < 1.14 as this is the
minimal required version to use static linking because of ABI changes in
core.
There is no way to dynamically ask Cargo to build static or dynamic lib
so we have to build both and pick the one we care when doing the meson
processing.
Fix#88
