SMPTE timecode parsed incorrectly (23.976 FPS)

[Sebastian-Brud-Tectonic]

Function in doc.js called extractTimeAndTickRate might contain a bug that seems like an impediment in development of one of our tools. The line

imscJS/src/main/js/doc.js

Line 1649 in 7716bcc

} else if ((m = CLOCK_TIME_FRAMES_RE.exec(str)) !== null) {

to be precise

The issues we currently face are:

1. parsing begin and end timecodes are regexp-based

   • it is cool and nice approach for resilient timecode picker, yet proved to not cover corner-cases (nonDropFrame encoding, etc.)
   • it ignores ttp:timeBase parameter's value (which is not a best practice)

2. timecode parser does not consider SMPTE cases with dropFrame encoding

   • it ignores attribute ttp:dropMode - not necessary to pass each Regex test
   • it does not cover Drop-Frame encoded timecodes (like library smpte-timecode does)

Few solutions I might think of (that would not affect the library itself too much):

1. allow passing custom timecode parser to imsc.fromXML function. Implementing Dependency Injection here is a nice way to get rid of multiple edge cases you would not want to cover and maintain by yourselves

2. implement standard-compliant parser that will cover all cases (Drop/Non-Drop Frame encoding, 2:3 pull-down on 23.976, etc.) - includes lot of effort implementing and preparing proper tests

3. make fromXML something more like a declarative pipeline ( where you can provide callbacks that can override parsing process steps - see: https://rxjs.dev/guide/higher-order-observables ) that processes the sax stream

4. become dependent on smpte-timecode library - worst solution IMHO. I like how you rely on sax parser, yet personally I prefer to have more control over dependencies I include into my codebase

[nigelmegitt]

The only permitted ttp:timeBase value in IMSC is media. As a reference IMSC player, it makes sense that it ignores ttp:dropMode since that only applies when ttp:timeBase="smpte".

Having said that, it's an interesting idea to refactor to allow injection of additional out-of-spec functionality.