Specifying the timecode source
For your captions to correctly synchronize with your video, you must set up your input timeline to match the timecodes embedded in your captions file. MediaConvert establishes the input timeline based on the value you choose for the input Timecode source setting. For more information, see Input timecode source and captions alignment.
For instructions on adjusting the Timecode source setting, see Adjusting the input timeline with the input timecode source.