gst-plugins-rs/video/closedcaption/src/lib.rs
Mathieu Duponchelle de796c95f0 tttocea608: refactor to fit more scenarios
- Report a latency:
  By design, tttocea608 will output buffers in the "past" when
  receiving an input buffer: we want the second to last buffer
  in the buffer list that we output to have the same pts as the
  input buffer, as it contains the end_of_caption control code
  which determines when the current closed caption actually gets
  displayed in pop_on mode. The previous buffers have timestamps
  decreasing as a function of the framerate, for up to potentially
  74 byte pairs (the breakdown is detailed in a comment).

  The element thus has to report a latency, at 30 frames per second
  it represents around 2.5 seconds.

- Refactor timestamping:
  Stop using a frame duration, but rather base our timestamps on
  a scaled frame index. This is to avoid rounding errors, and
  allow for exactly one byte pair per buffer if the proper framerate
  is set on the closed caption branch, and the video branch has
  perfect timestamps, eg videorate. In practice, that one byte
  pair per frame requirement should only matter for line 21 encoding,
  but we have to think about this use case too.

- Splice in erase_display_memory:
  When there is a gap between the end of a buffer and the start
  of the next one, we want to erase the display memory (this
  is unnecessary otherwise, as the end_of_caption control code
  will in effect ensure that the display is erased when the
  new caption is displayed). The previous implementation only
  supported this imperfectly, as it could cause timestamps to
  go backwards.

- Output last erase_display_memory:
  The previous implementation was missing the final
  erase_display_memory on EOS

- Output gaps

- Write more tests

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/314>
2020-04-23 20:10:42 +02:00

74 lines
2.2 KiB
Rust

// Copyright (C) 2018 Sebastian Dröge <sebastian@centricular.com>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public
// License as published by the Free Software Foundation; either
// version 2 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public
// License along with this library; if not, write to the
// Free Software Foundation, Inc., 51 Franklin Street, Suite 500,
// Boston, MA 02110-1335, USA.
#![crate_type = "cdylib"]
#![recursion_limit = "128"]
// These macros are in weird paths currently,
// and extern crate is used to avoid the explicit imports
// should not be needed ideally in the upcoming releases.
// https://github.com/gtk-rs/glib/issues/420
// https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/issues/170
#[macro_use]
extern crate glib;
#[macro_use]
extern crate gst;
#[macro_use]
extern crate lazy_static;
extern crate gstreamer_sys as gst_sys;
#[cfg(test)]
#[macro_use]
extern crate pretty_assertions;
mod cea608tott;
#[allow(non_camel_case_types, non_upper_case_globals)]
#[allow(clippy::redundant_static_lifetimes, clippy::unreadable_literal)]
#[allow(clippy::useless_transmute, clippy::trivially_copy_pass_by_ref)]
pub mod cea608tott_ffi;
mod line_reader;
mod mcc_enc;
mod mcc_parse;
mod mcc_parser;
mod scc_enc;
mod scc_parse;
mod scc_parser;
mod tttocea608;
fn plugin_init(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
mcc_parse::register(plugin)?;
mcc_enc::register(plugin)?;
scc_parse::register(plugin)?;
scc_enc::register(plugin)?;
cea608tott::register(plugin)?;
tttocea608::register(plugin)?;
Ok(())
}
gst_plugin_define!(
rsclosedcaption,
env!("CARGO_PKG_DESCRIPTION"),
plugin_init,
concat!(env!("CARGO_PKG_VERSION"), "-", env!("COMMIT_ID")),
"LGPL",
env!("CARGO_PKG_NAME"),
env!("CARGO_PKG_NAME"),
env!("CARGO_PKG_REPOSITORY"),
env!("BUILD_REL_DATE")
);