Reuse transceivers in subscribe path

[boks1971]

LK-22 (https://linear.app/livekit/issue/LK-22/feature-pooled-transceivers-to-avoid-re-negotiation)

Do not stop remote tracks. That would change readyState of track
to ended and the corresponding transceiver cannot be reused.
Instead use the enabled attribute of track to enable/disable
remote tracks.

Bumping up the protocol version that informs the server that
client is capable of reusing transceivers.

Testing:

Connect from Chrome. For remote side, connect/disconnect
from Firefox several times and ensure the following

• SDP does not grow (it has 4 sections as reported by
  chrome://webrtc-internals (version, data, audio, video) each
  time the remote side connects.
• Media flows from remote side on every connection.

Oddities:

• Chrome callback ontrack sends a track. When the remote side
  reconnects and the same transceiver is used, the callback does
  not contain the new track id. It retains what was returned in the
  first callback. Don't think it is an issue as we do not use that
  track id anywhere.

[davidzhao]

This looks great!

Don't think it is an issue as we do not use that track id anywhere.

It does pass us a new stream id though? I think that's the more important piece. FWIW, we do use the track id here, only if it's not already encoded in the stream id. (Room.onTrackAdded)

const parts = unpackStreamId(stream.id);
const participantId = parts[0];
let trackId = parts[1];
if (!trackId || trackId === '') trackId = mediaTrack.id;

[boks1971]

@davidzhao Yes I verified that the stream id and the parsing gets the new information. I will verify it again just to be doubly sure.

[davidzhao]

great! lg

[boks1971]

Re-confirming that the stream id shows the right stuff on a reconnect/reuse of transceivers

remote stream:  MediaStream {id: 'PA_XuF28UHg9G3C|TR_SvjS2hYhdRfH', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_XuF28UHg9G3C|TR_SvjS2hYhdRfH
onTrackAdded @ Room.ts:236
(anonymous) @ Room.ts:83
emit @ events.js:153
subscriber.pc.ontrack @ RTCEngine.ts:185
wrappedCallback @ utils.js:46
Room.ts:236 remote stream:  MediaStream {id: 'PA_XuF28UHg9G3C|TR_Snaw3Gr6svq5', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_XuF28UHg9G3C|TR_Snaw3Gr6svq5
onTrackAdded @ Room.ts:236
(anonymous) @ Room.ts:83
emit @ events.js:153
subscriber.pc.ontrack @ RTCEngine.ts:185
wrappedCallback @ utils.js:46
Room.ts:236 remote stream:  MediaStream {id: 'PA_REbbQ2qJpmPK|TR_2Q6eoEgCrfQC', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_REbbQ2qJpmPK|TR_2Q6eoEgCrfQC
onTrackAdded @ Room.ts:236
(anonymous) @ Room.ts:83
emit @ events.js:153
subscriber.pc.ontrack @ RTCEngine.ts:185
wrappedCallback @ utils.js:46
Room.ts:236 remote stream:  MediaStream {id: 'PA_REbbQ2qJpmPK|TR_fz7yT4G5PLzZ', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_REbbQ2qJpmPK|TR_fz7yT4G5PLzZ
onTrackAdded @ Room.ts:236
(anonymous) @ Room.ts:83
emit @ events.js:153
subscriber.pc.ontrack @ RTCEngine.ts:185
wrappedCallback @ utils.js:46
Room.ts:236 remote stream:  MediaStream {id: 'PA_DUknmHLikjXn|TR_kYqUhvNcnGqn', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_DUknmHLikjXn|TR_kYqUhvNcnGqn
onTrackAdded @ Room.ts:236
(anonymous) @ Room.ts:83
emit @ events.js:153
subscriber.pc.ontrack @ RTCEngine.ts:185
wrappedCallback @ utils.js:46
Room.ts:236 remote stream:  MediaStream {id: 'PA_DUknmHLikjXn|TR_4irgCrcnnZ8i', active: true, onaddtrack: null, onremovetrack: null, onactive: null, …} PA_DUknmHLikjXn|TR_4irgCrcnnZ8i