The track initialization data of Tx3g includes default style values for
font styles, colour, and font family. Additionally the decoder now supports
vertical subtitle placements other than the Tx3g default of 85% video height.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152930057
Extended Tx3gDecoder to read additional information after subtitle text.
Currently parses font face, font size, and foreground colour.
Font identifier and other information provided in subtitle sample description
not yet supported.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152793774
