Use cases for time delta
How you use Time delta (TimeDelta) depends on the problem you're trying to solve and the captions format that you're working with.
By default, you specify the time delta in seconds. If you want to specify it in milliseconds instead, set Time delta units (TimeDeltaUnits) to Milliseconds (MILLISECONDS).
Adjusting for different timecodes between video and captions files
With timecode-based captions formats, such as SCC and STL, the timecodes in the captions might be relative to a starting timecode that is different from the starting timecode embedded in the video. You use Time delta to adjust for the difference.
Example problem: Your video file might have embedded timecodes that start at 00:05:00:00. The first instance of dialogue that requires captions might be one minute into the video, at timecode 00:06:00:00. Your captions file might be written on the assumption that your video timecodes start at 00:00:00:00, with the first caption starting at 00:01:00:00. If you don't use Time delta, MediaConvert would not include this first caption because it occurs before the start of the video.
Solution: Add five minutes to the captions. Enter
300 for Time delta.
Adjusting captions after synchronizing video and audio
Your timecode-based (SCC or STL) captions might be aligned with the timecodes that are embedded in your video, but you might need to use the input Timecode source setting to align your audio. This creates a difference between the video and captions, which you need to adjust for. You don't need to make this adjustment with timestamp-based captions formats, such as SRT, SMI, and TTML.
For more information about aligning captions when you use input Timecode source, see Input timecode source and captions alignment.
Example problem: Your video file might have embedded timecodes that start at 00:05:00:00 and the first instance of dialogue that requires captions might be one minute into the video, at timecode 00:06:00:00. Your captions file is written to sync correctly, with the first caption starting at 00:06:00:00. But you need to change your embedded captions in your input to sync correctly with your audio file. So you set the input Timecode source to Start at Zero. If you don't use Time delta, MediaConvert would put the first caption in your output at six minutes into the video.
Solution: Subtract five minutes from the captions. Enter
-300 for Time delta.
Correcting slight errors in captions sync
With any type of sidecar format, there might be a small error in your input captions file, so that the captions are consistently a little late or a little early.
Example problem: Your video has embedded captions that start at zero. The first instance of dialogue that requires captions is at 00:06:15:00, but the captions appear on the screen three seconds late, at 00:06:18:00.
Solution: Subtract three seconds from the captions.
Enter -3 for Time delta.