Enum TrackVideoEncoder 

#[non_exhaustive]
pub enum TrackVideoEncoder {
    PreEncoded(PreEncodedOptions),
    Inline(InlineEncoderCallback),
}

How a video track produces its encoded bitstream, replacing libwebrtc’s builtin encoder for that track only.

One mechanism, two feeding styles:

• PreEncoded — asynchronous: you push already-encoded bytes at your own pace, from any thread (a hardware encoder callback, a relay, a file dumper). A queue decouples your producer from the encoder thread. The track comes back as LocalVideoTrack::Encoded and you feed it with [EncodedVideoTrack::push_encoded_frame].
• Inline — synchronous: libwebrtc calls your closure on the encoder thread with every raw I420 frame; return Some(encoded) to inject bytes into the RTP stack or None to drop the frame. Right when your pipeline is raw-in/encoded-out and you want libwebrtc to drive the cadence. The track comes back as LocalVideoTrack::Raw and you feed it like any raw track.

Either way, the bytes you produce must match the codec negotiated for the track’s transceiver — read RawVideoFrame::codec (inline) or set codec preferences to pin it.

Slot assignment order — positional, with fresh upgrades

Slots route encoder instances ↔ tracks positionally: reservation order (track creation) must match the negotiation order of the transceivers carrying those tracks. Create encoder-carrying tracks before the peer connection they’re attached to negotiates (before create_offer), or the registry may not yet see a reservation to bind to; ordering across multiple peer connections sharing one factory follows whichever negotiates first, not track creation order.

Dropping an encoder-carrying track retracts its pending slots and degrades any surviving assigned slot to Builtin (loud fallback, never another track’s). libwebrtc may recreate encoder instances on internal errors or renegotiation past a dead track; that path degrades the same way rather than re-routing another live track’s pipeline.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

PreEncoded(PreEncodedOptions)

You push already-encoded bytes at your own pace.

Inline(InlineEncoderCallback)

libwebrtc calls your encoder synchronously with every raw I420 frame.