C.9 Automatic Caption Erasure (Preferred)
[...]
Some manufacturers have suggested building automatic timeout into their
decoders. They propose that if no data are received for the selected caption
channel within a given time, the decoder should automatically erase the
caption. Such erasure may supersede the intentions of the caption service
providers and institute one maximum display time for all captioning services.
If such a timeout is deemed necessary, however, the time limit should be no less
than 16 seconds, an amount of time said by caption service providers to be longer
than their most enduring caption. It is preferred, when automatic caption erasure
is used in a decoder, that only displayed memory be erased, since some caption
service providers may, contrary to recommended practice (see Section B.8.3), send
pop-on style caption data to non-displayed memory more than 16 seconds before
sending the EOC command which causes the caption to display.
In this mode, cues are output as soon as they are ready for
display, without a duration. This can be useful in live mode,
when downstream is OK with determining the duration after the
fact, through clear=True.
The consequence of this is that the current roll-up window will
be output repetitively, it is up to downstream to deal with that
how it prefers.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/554>
There is no point to that, the code is already factored in such
a way that erase_display_memory is inserted at the correct time,
including while loading the next pop-on captions in non displayed
memory.
Locking order of state and settings was inconsistent, and causing
deadlocks. Fix and document it, consistently drop locks before
chaining up events / pushing and avoid sequentially unlocking /
relocking settings in the same local code path.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/539>
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>
As stated in the spec:
> In addition, the user must have the capability to select a black
> background over which the captioned letters are displaced.
The property is MUTABLE_PLAYING
In roll-up modes, we open new lines when the last column is reached.
This commit implements lookahead on a word basis, in order to avoid
splitting words unless absolutely necessary (when a word won't fit
on a full row)
Trying to write "" in order to erase characters in the caption
frame simply fails silently, the proper way to implement
delete_to_end_of_row and backspace was to memset the relevant
cells.
This element outputs the same format expected by tttocea608 in
json mode.
It notably differs from cea608tott in that it only uses libcaption's
low-level API, as it needs to maintain its own view of the current
state of the screen, and make fine-grained decisions as to when
to output data and how to timestamp it.
It covers a large portion of the 608 spec, with the exception of
a few features that probably haven't ever seen widespread usage,
those are listed in a TODO list at the top.
It has been tested with a reference file produced by CEA and covers
all the features it demonstrates.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/480>
