Closed Captioning with CaptionSync allows you to get Subtitles or Open Captions using our Video Encoding feature. This article describes the differences between Subtitling and Open Captioning.
Most captioning for web content uses standalone caption files - these files contain the caption data separately from your video. There are, however, circumstances where you may want to encode the caption data back into your video file. Common reasons for doing this are to support iOS devices (which do not currently support standalone caption files), to eliminate the need to reference a standalone caption file, or to support playback devices that do not support closed captioning. See detailed information about using our Video Encoding feature in our tutorial.
In Subtitling, we encode the caption data into the subtitle track of your mp4. This operation does not re-encode the video or audio components of your mp4; it merely merges in the caption data. Once merged, the resulting mp4 will present a subtitle option on any mp4 player that supports the subtitle track (including all iOS players, AppleTV, iTunes, QuickTime, JW Player, Flow Player, VLC, RealPlayer, and many others). Most browsers also display subtitles with MP4/M4V videos. Those include (on Windows) Firefox, Internet Explorer and Opera.
- On Windows, some players, like iTunes and QuickTime, need the file to have the .m4v extension to display the subtitles. So, after you download the encoded output, ensure you change the extension to .m4v, e.g., Bio_1.mp4 -> Bio_1.m4v .
- Currently, Windows Media Player doesn't support subtitles display with mp4/m4v files.
- The player renders the subtitles at play time, and so, many settings, like the text pane size, are governed by the player itself.
- Learn how to turn on subtitles on some of the most common players in this section of our Support Center.
Open Captioning is quite different – in open captioning, the caption data is rendered right into the video picture. To do this, we must re-encode your video and alter the image to include the caption text. Once complete, the caption text is part of the video - it no longer exists separately from the video. The advantage of this is that it will display on any device that displays the video - you can't turn them off; no support for captioning is necessary. The disadvantage is that the text is now part of the video - it will scale with the video, and distort if you change the aspect ratio. Generally, open captioning is only recommended as a last resort - when you must provide captioning on a playback device that provides no support for captioning or subtitling.
Open captions are typically placed below your video pane, so the aspect ratio of your video will change slightly.
The process of open captioning requires us to transcode your video, which can affect the video quality and file size.
With Open Captioning, since the player cannot control any of the rendering anymore, some aspects will be no longer controlled by the user:
- The user cannot turn captions off;
- The user/player cannot control the size of the text (so the text simply scales with the video size);
- The user/player cannot control the color, position or any other attributes of the text;
- The caption data is not available to screen readers for accessibility;
- The caption data is not usable for search features (it is just pixels now, not text anymore).