Browsers have some interesting behavior around text tracks / captions. This document outlines those differences in behavior.

• Open Chromium issue
• If there is no <track> with a default attribute, a <track> with srclang matching the client's locale (i.e. system locale) will be used. For example, if your system language is French, a <track> with srclang="fr" will be played without your input.

• Firefox will not play any track by default unless it has the default attribute.

• IE9, IE10, and IE11 will not play any track by default unless it has the default attribute.

• On OS X, if there is no <track> with a default attribute, a <track> with srclang matching the client's locale (i.e. system locale) will be used. For example, if your system language is French, a <track> with srclang="fr" will be played without your input.

• The list of languages is sorted with alphabetically with the language matching the phone's locale promoted to the top of the list.
• Choosing a language manually in the native player (iPhone) will set an internal preference at the OS level for captions in that language. This preference survives clearing the browser cache and rebooting the phone.
• Using a default attribute does not seem to be respected for captions, but is for subtitles. In the case of subtitles, it overrides any previously user-selected language on the next page load.
• When "Auto (Recommended)" is selected in the captions/subtitles list, the first/locale language captions/subtitles are played.
• The "Unknown CC" option appears occasionally and is an iOS feature.