Sync - Global Drift Early (Text)
Timed Text framerate is incorrect resulting in a sync drift where events become progressively earlier than their audio cues.
The subtitles are running at a faster framerate than the video. When the video is 23.976 fps, it is possible that the only thing needed would be a metadata only redelivery with the proper timing value set. There is a lot of confusion about the difference between timing using SMPTE24 timecode reference or MediaTime reference, so please be sure to determine what timing reference is used for the timed-text asset.
The following article outlines a method for confirming which timing reference your file is using:
How do I know whether to select 'SMPTE' or 'MEDIA' for a timing reference?
If your investigation leads you to believe that these sync issues are attributed to an incorrect timing reference being specified in Backlot, you can confirm this by accessing the "transfer details" window accessible via the "Deliveries" tab:
Look for discrepancies between your transfer's "Delivery Metadata" (information specified by end-users prior to delivery) and the "Technical Metadata" (information/metadata derived from technical inspections post delivery), as shown below:
*Note: If NO value is selected, the asset(s) will process through as SMPTE timing.
After you have confirmed that this issue is attributed to SMPTE/MEDIA confusion, please reach out to your Netflix Representative and ask for the redelivery request to be updated to "Metadata Only".
If this is not simply attributed to SMPTE / MediaTime confusion, convert the framerate of the file to match the video's framerate. This can be achieved quite easily by using your subtitling tools built in timecode converter to go from one framerate to another with one click. For scenarios where this quick fix isn't perfect, you can utilize the software's "shrink/stretch" feature to adjust the timecode of the last event to a timecode that you manually specify.