TFDT stands for "Track Fragment Decode Time" and is a term used in multimedia file formats. In the context of a multimedia file format such as MP4, a track fragment is a portion of a track that holds encoded media data. The Track Fragment Decode Time, as the name suggests, is the time required to decode the encoded media data contained in the track fragment.
Track fragments can be used to store media data in a more efficient manner, as they can be decoded in parallel, reducing the overall decoding time. Additionally, track fragments can also be used to store partial media data, allowing for more efficient streaming and playback.