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rvalue c96a2a64fc libcaption: Optimize branch conditons 
The optimization silences the warning about type limits on platforms
with `char` type as `unsigned char`.

The original condition is semantically identical to the optimized one
because the signed-to-unsigned cast is well-defined in C standard.
2024-01-03 18:20:38 -05:00
..
caption deps: Replace invocations of sprintf with snprintf 2022-11-11 19:51:27 +01:00
cmake cmake: Add changes for CMake build framework 3.0 2023-03-26 18:20:38 -04:00
src libcaption: Optimize branch conditons 2024-01-03 18:20:38 -05:00
.clang-format clang-format: Add clang-format files 2019-06-23 01:53:56 -07:00
.gitignore Add libcaption library 2016-12-23 10:37:06 -08:00
CMakeLists.txt deps: Update CMake target source lists with alphabetic sorting 2023-12-19 17:59:44 -05:00
Doxyfile.in Add libcaption library 2016-12-23 10:37:06 -08:00
format.sh Add libcaption library 2016-12-23 10:37:06 -08:00
LICENSE.txt libobs: Update libcaption library 2018-07-08 01:14:27 -07:00
README.md libobs: Update libcaption library 2018-07-08 01:14:27 -07:00

README.md

version

v0.8 Matthew Szatmary m3u8@twitch.tv / matt@szatmary.org

libcaption

libcaption is a library written in C to aid in the creating and parsing of closed caption data, open sourced under the MIT license to use within community developed broadcast tools. To maintain consistency across platforms libcaption aims to implement a subset of EIA608, CEA708 as supported by the Apple iOS platform.

608 support is currently limited to encoding and decoding the necessary control and preamble codes as well as support for the Basic North American, Special North American and Extended Western European character sets.

708 support is limited to encoding the 608 data in NTSC field 1 user data type structure.

In addition, utility functions to create h.264 SEI (Supplementary enhancement information) NALUs (Network Abstraction Layer Unit) for inclusion into an h.264 elementary stream are provided.

H.264 utility functions are limited to wrapping the 708 payload into a SEI NALU. This is accomplished by prepending the 708 payload with 3 bytes (nal_unit_type = 6, payloadType = 4, and PayloadSize = variable), and appending a stop bit encoded into a full byte (with a value of 127). In addition if the 708 payload contains an emulated start code, a three byte sequence equaling 0,0,1 an emulation prevention byte (3) is inserted. Functions to reverse this operation are also provided.

Characters
BNA ! " # $ % & ’ ( ) á + , - . /
BNA 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
BNA @ A B C D E F G H I J K L M N O
BNA P Q R S T U V W X Y Z [ é ] í ó
BNA ú a b c d e f g h i j k l m n o
BNA p q r s t u v w x y z ç ÷ Ñ ñ █
SNA ® ° ½ ¿ ™ ¢ £ ♪ à   è â ê î ô û
WES Á É Ó Ú Ü ü ‘ ¡ * ' — © ℠ • “ ”
WEF À Â Ç È Ê Ë ë Î Ï ï Ô Ù ù Û « »
WEP Ã ã Í Ì ì Ò ò Õ õ { } \ ^ _ | ~
WEG Ä ä Ö ö ß ¥ ¤ ¦ Å å Ø ø ┌ ┐ └ ┘
  • BNA = Basic North American character set
  • SNA = Special North American character set
  • WES = Extended Western European character set : Extended Spanish/Miscellaneous
  • WEF = Extended Western European character set : Extended French
  • WEP = Extended Western European character set : Portuguese
  • WEG = Extended Western European character set : German/Danish

Limitations

Current B-frame support for caption creation is minimal. libcaption ensures no re-ordering of captions is required on playback.

Build Directions

Mac Os/Linux

Install build dependencies (git, cmake, a compiler such as xcode, gcc or clang and optionally re2c and ffmpeg)

  • run cmake . && make
  • or to compile without re2c cmake -DENABLE_RE2C=OFF . && make
  • finally sudo make install to install

Windows

I have never tested libcaption in windows. It is written in pure C with no dependencies, so there is no reason it would not work.