Tech Tip - SMPTE-TT Caption Insertion
Easy insertion of captions into a MPEG stream
PixelTools products products can add captions defined in a SMPTE-TT (SMPTE 2052) file during MPEG encoding or to an existing MPEG stream without transcoding.
Demo of SMPTE-TT Caption Insertion
Download the SMPTETTdemo.zip file to obtain a demo of MPEGRepair that inserts captions defined in a SMPTE-TT file during encoding. Run the LaunchDemo.bat file to start the demo. The tool inserts captions into a short stream and then decodes the stream allowing you to verify the inserted captions.
Inserting SMPTE-TT Captions during MPEG encoding
PixelTools’ encoding products including MPEGRepairHD, ExpertHD and HDProQT can insert captions defined in a SMPTE-TT file into a MPEG file during encoding. The captions can be inserted per the legacy specifications of CEA-708, CEA-608, ATSC, SCTE20, DVD, or combinations of the above. The SMPTE-TT captions can also be encoded as Open Captions IE burned into the video so they are always displayed.
Inserting SMPTE-TT Captions into and existing stream
PixelTools’ decoding products including MPEGRepairHD and ExpertCaption can insert captions defined in a SMPTE-TT file into an existing MPEG stream without transcoding. The captions can be inserted per the legacy CEA-708, CEA-608, ATSC, SCTE20, DVD, or combinations of the above.
The US Federal Communication Commission (FCC) has issued a ruling that all Internet content streaming after 30 March 2014 must include captioning. The Society for Motion Pictures and Television Engineers (SMPTE) has published a set of specifications (SMPTE 2052) that define a captioning format that can describe current and future captioning requirements. The FCC has not specified which closed captioning format is to be used in Internet streaming, but has recommended SMPTE-TT as a “safe harbor”.
The SMPTE-TT format is an XML like text structure that is based upon WC2 TTML. TT stands for timed text. The SMPTE-TT format can provide all of the information needed to create/ preserve legacy CEA-608 and CEA-708 captioning. It also includes information that can be used to enhance the legacy captioning such as a custom fonts and updated captioning locations on the screen. The SMPTE-TT can also define bit-map graphics as used in DVB subtitles by encoding the pixels as ASCII text characters to fit into the XML text.
PixelTools products currently input SMPTE-TT captions and convert them into the user selected legacy format for embedding into MPEG streams. Future PixelTools products will insert SMPTE-TT captions directly into MXF and MPEG streams as required by video streaming standards.
An example of a SMPTE-TT file used to describe legacy CEA-608 captions is presented in SMPTE RP 2053-10:2012. In this example, POP Up captions are detailed.
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