Struct ReferenceSlots 

pub struct ReferenceSlots { /* private fields */ }

The buffers a VP8 or VP9 encoder predicts from, with the frame each holds and whether a client reported it lost.

Some buffers are spent on anchors older than the last few frames, so a loss up to twelve frames deep still finds a frame older than it. VP8 has three, LAST, GOLDEN, and ALTREF: every frame lands in LAST, and every twelfth in GOLDEN and ALTREF by turns, so one anchor is always twelve to twenty-three frames old. VP9 has eight: the last four frames by turns in the first four, and every fourth frame by turns in the other four, the oldest twelve to fifteen frames back. A frame predicts from the newest buffer whose frame the client still has, the first such buffer when others are as new, and a VP8 frame coded from an anchor rather than LAST refreshes all three, since it is the newest picture both sides hold. The frame ids wrap; the timestamps are the session’s own count of encoded frames and do not, and the recent ones are kept so a lost frame no buffer holds still dates the buffers coded after it.

Implementations

impl ReferenceSlots

pub fn new() -> Self

VP8’s three buffers.

pub fn vp9() -> Self

VP9’s eight buffers.

pub fn next_pts(&self) -> u64

The timestamp the next frame is encoded with.

pub fn acknowledge(&mut self, frame_id: u16, held: bool) -> bool

Note that every consumer holds frame_id, or where not held was sent it, as ReferenceWindow::acknowledge does: the anchor buffer holding the newest frame they all hold is then pinned, and one they were all sent is kept until they hold it (PENDING_PERIODS). False for a frame not remembered or from before the key frame.

pub fn shared_anchor(&self, plan: SlotPlan) -> bool

Whether a frame coded under plan is an anchor on the schedule predicting from a buffer holding a frame every consumer was sent, so each can decode it (FRAME_ANCHOR). One predicting past a loss is not flagged: a consumer it reaches takes it as the end of its run, while a flagged one would wait for room behind the consumer’s queue.

pub fn has_reference(&self) -> bool

Whether a frame not coded as a key frame has a buffer left to predict from.

pub fn slot(&self, slot: u8) -> Option<(u16, u64, bool)>

What each buffer holds: the frame’s id and timestamp and whether it was reported lost.

pub fn plan(&self, key: bool) -> SlotPlan

The buffer the next frame predicts from (the newest one the client still has) and the buffers it refreshes; a key frame refreshes all of them and predicts from none.

pub fn record(&mut self, frame_id: u16, plan: SlotPlan) -> Reference

Record the frame just encoded under plan and answer what it predicted from.

pub fn invalidate(&mut self, frame_id: u16) -> Invalidation

Leave frame_id and every frame encoded after it out of the references.

Trait Implementations

impl Default for ReferenceSlots

fn default() -> Self

Returns the “default value” for a type.