Seekable

Seekable refers to the ability to reposition a read or write pointer within a data sequence and then access data from that new position. A seekable data source supports random access, allowing efficient movement to arbitrary offsets without reading the entire content sequentially. In software, seekability is often exposed through operations or methods such as seek and tell, and the object may implement a seekable interface or API.

Whether a stream is seekable depends on the underlying source. Regular files on a disk or in-memory buffers are typically seekable. Pipes, sockets, and many network streams are not, since data arrives in sequence and there is no efficient way to jump to a past position. Some network protocols enable seeking via range requests or indexing (for example, HTTP range requests or media streams with an index). File formats may be designed to be seekable by maintaining an index of data offsets; formats like MP4 or MKV allow jumping to specific timestamps. Other formats, especially compressed or encrypted streams, may require full decoding to reach a point, or may only support seeking to certain boundaries such as keyframes.

In practice, seekability affects performance and features: editors, media players, and databases often rely on random access; non-seekable streams are suitable for sequential consumption or live data. Limitations include potential imprecision when seeking and the need for indices or decoding constraints.

See also: random access, seek, index, keyframe, range request.