avcodec/webvttenc: add webvtt encoder

Based off the srt encoder. The following features are unimplemented:

- fonts, colors, sizes
- alignment and positioning

The rest works well. For example, use ffmpeg to convert subtitles into the .vtt format:

  ffmpeg -i input.srt output.vtt

Signed-off-by: Aman Gupta <ffmpeg@tmm1.net>
Signed-off-by: Clément Bœsch <u@pkh.me>

1 files changed, 1 insertions, 0 deletions

diff --git a/Changelog b/Changelog
index 3e10b2001e..3d416c4d2f 100644
--- a/Changelog
+++ b/Changelog
@@ -25,6 +25,7 @@ version <next>:
 - libx264 reference frames count limiting depending on level
 - native Opus decoder
 - display matrix export and rotation api
+- WebVTT encoder
 
 
 version 2.2: