Question: In a 3GPP file format (3GP), what is the primary purpose of the Track Fragment Base Media Decode Time ('tfdt') Box in relation to random access within a file?
Option 1: To provide the presentation timeline after applying edit lists or similar structures.
Option 2: To offer an alternative to the Decoding Time to Sample Box for sample durations.
Option 3: To enable calculation of the decode time of the first sample in a track fragment without summing preceding sample durations.
Option 4: To define the media's timescale for all tracks within a file.
Explanation: The correct answer, Option 3, highlights the key benefit of the 'tfdt' Box as described in the context - facilitating random access by providing the decode time of the first sample in a track fragment without needing to calculate from preceding samples. This directly relates to efficient playback and navigation within multimedia files. Options 1, 2, and 4 are incorrect because they either misrepresent the box's purpose (Option 1), suggest an unnecessary duplication of function (Option 2), or overstate its scope (Option 4).