The Start Time information is most usually found in video files, but can also occur in audio or image files. It has most significance in video files such as MOV, MP4 or AVI though. Thus, this entry will concentrate on explaining the Start Time metadata found in such files.
The Start Time is used in order to synchronize different elements in a video, such as video and audio stream and even subtitles or comments. It is usually given in milliseconds or seconds. The Start Time marks the timestamp of the very first frame of the video. Depending on the container format (e.g. MP4 vs. AVI), the Start Time can vary or even show a negative value. This doesn’t mean that frames are missing from a video, but that the frame rate differs between the files inside the video container.
The Start Time can be represented in your file in a different way as well. One of them is noted as “PTS” which stands for Presentation Time Stamp. It also sets the start of the first frame of a video. While the Start Time is usually given in seconds, PTS uses samples or timebase units as a value.