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I'm starting a tutorial video podcast and have recorded a couple of episodes.

I've captioned them, and have the captions file in .srt format. However I haven't yet found a way to embed that file in the .mp4 video file that makes the captions optional for podcast viewers.

How can the captions be included with the podcast, so that viewers can turn them on only if they want them, but they will be off by default? I'm most interested in getting this working in the iTunes podcast section and the iOS Podcast app to start with (although a universal solution that works with all podcast clients would be great).

UPDATE 3rd April 2014:

No luck yet I'm afraid with solving this. Until something better comes along, in the podcast feed, for each <item>, I set the <link> element to a URL that hosts a version of the video with optional captions (captions are off by default), and towards the end of the body of the <description> element I repeat the same URL mentioning alongside it that subtitles are available there. See if you'd like to see an example.

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Just so you know, if you come up with your own solution (even partial) like you described in your update, you can feel (and are encouraged) to post an answer to your own question. – AJ Henderson Apr 3 '14 at 18:17

Ordinarily, I'd create an Adobe AIR or AIR-for-iOS app to solve this problem. You'd just sychronize your captions to cue points in the video and make 'em visible or invisible with a programmed-in button. You could easily have multiple languages in this way.

Are iTunes podcasts just flat-out mp4 movies?

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The video podcasts in iTunes are mp4 files. I think .m4v might be supported too in case that helps. – Eliot Sykes Mar 23 '14 at 13:12
I think that, by definition, a flattened movie file of any type can't do this. You can, of course, add captions to the video but to have an optional on-off button you'll have to graduate to a more programmatic way of packaging video. – Craig Mar 23 '14 at 20:56

Have you tried WebVTT for marking up the subtitles? is a surprisingly good tool for making captions. You could also cheat a bit and use Youtube's pretty good voice recognition to perhaps save time transcribing.

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