Overview: Subtitle overlay pipelines

Subtitle overlay pipelines connect decoding, subtitle composition and output encoding through a particular sequence of stages.

A working overlay needs compatible connections between the stages, not just a filter that can run in isolation. Picture location, transfers and synchronization influence that sequence. The fundamental, classic, filtering and hardware pipeline pages show how the arrangement changes while keeping the intended subtitle presentation recognizable.

• Subtitle overlay pipeline fundamentals
  A subtitle overlay pipeline joins two timed branches: decoded video and interpreted captions. Correct output depends on representation, geometry, alpha, colour, resources and memory boundaries.

• Classic subtitle overlay pipeline
  The classic subtitle route lets a video filter own script reading and libass rendering, then composes into CPU pictures before output encoding.

• Subtitle filtering pipeline
  Native subtitle filtering keeps decoded text or graphics in a separate timed branch, exposing transformations before direct composition or conversion into an image/video layer.

• Hardware subtitle overlay pipeline
  A hardware subtitle pipeline separates codec engines, CPU text preparation, device composition and memory transfers; accepted formats and timed image updates determine the usable route.