Calculate offset based on `ebuttm:documentStartOfProgramme`

[nigelmegitt]

When converting from timebase="smpte" to timebase="media" it would be ideal to offer a setting (or indeed make it the default) to use the value of TCP or equivalently ebuttm:documentStartOfProgramme as the offset and discard any content that falls before that timecode.

For example, an EBU-TT document is created from an STL document and has:

• timebase="smpte",
• a 'subtitle zero' at 00:00:00,
• a ebuttm:documentStartOfProgramme="10:00:00" and
• most of the content falls after 10:00:00.

This should generate an EBU-TT-D document with:

• timebase="media",
• no subtitle zero
• the content is offset backwards by 10:00:00: an element whose begin="10:00:00" in the EBU-TT should have begin="00:00:00" in the EBU-TT-D.

[andreastai]

Yes this makes sense and was also raised by other parties who use the script to convert "broadcast" subtitles to "internet" subtitles.

The solution may as simple as to have a new parameter (e.g. offsetTcp or offsetSop for offset Start of program) and to set the value of the "offsetInFrames" parameter accordingly. The processing should stop if offsetTcp AND offsetInSeconds and offsetInFrames have been specified.

[spoeschel]

Sorry for the quite long delay!

We will add respective parameters to STLXML2EBU-TT and EBU-TT2EBU-TT-D that will use the TCP/ebuttm:documentStartOfProgramme values, to adjust all timecodes accordingly.

[spoeschel]

The example also affects the subtitle zero, which is already covered by #13. Therefore we will address that specific aspect there (distinct from the resolution of this issue here).

[spoeschel]

Fixed in version 1.0.