[extractor/common] Improved support for HTML5 subtitles

Ref: #10625

In a strict sense, <track>s with kind=captions are not subtitles. [1]
openload misuses this attribute, and I guess there will be more
examples, so I add it to common.py.

Also allow extracting information for subtitles-only <video> or <audio>
tags, which is the case of openload.

[1] https://www.w3.org/TR/html5/embedded-content-0.html#attr-track-kind

1 files changed, 6 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index a1c4df479..ebe4ff0e8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+vesion <unreleased>
+
+Core
++ Improved support for HTML5 subtitles
+
+
 version 2016.09.24
 
 Core