Captions provide viewers with information about what is occurring in their videos for viewers who are not able to understand or hear the language, and many streaming services, such as Netflix, YouTube, and Hulu, support captions to increase accessibility.

Open Captions vs Closed Captions

Open Captions

Closed Captions

Options for Closed Captions

You can confirm what type of caption formats are supported by ExoPlayer below.

TTML

Once you have the TTML file, you can show the captions using ExoPlayer.

If you are interested in how and where ExoPlayer parses a TTML file, you can check TtmlDecoder.java.

WebVTT

Once you have the WebVTT file, you can show the captions using ExoPlayer.

If you are interested in how and where ExoPlayer parses a WebVTT file, you can check WebvttDecoder.java.

TTML/WebVTT into Box

If you use mp4 file-based streaming, you can put caption data into a box. How you can put those caption data into a box can be confirmed from ISO/IEC 14496–30.

CEA-608/CEA-708

You can play a media file with CEA-608 embedded from this link.

Summary

Android Engineer at AbemaTV Github: https://github.com/takusemba

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