closedCaptions

The closed captions this picture carried, the cc_data of its ATSC A/53 data, three bytes per caption pair, as broadcast H.264, HEVC and MPEG-2 carry them inside the video, or null when it carried none (#236). Read once by the engine as the frame leaves its decoder, so a decoder hands out frames in the order they are shown, which is the order the captions were written in.

The engine makes them a subtitle track of its own, CC1, from the first picture that carries any: a stream whose codec is CLOSED_CAPTIONS_CODEC, each of whose packets holds one picture's bytes at the picture's time, decoded by whichever SubtitleDecoderFactory takes that codec. A frame decoded where these bytes cannot be read, such as one a platform decoder writes straight to a surface, answers null.