4.1 KiB
4.1 KiB
| title |
|---|
| quic |
GStreamer
Existing implementations which support stream and datagram multiplexing are
gst-quic-transport
Few points to think about before hand
- Flow control
- Stream credits
- Priority among streams
rtpquicmux
- Adds the flow identifier
- Maps RTP and RTCP packets to QUIC streams or datagram
- Each payload type and SSRC is send on a unique QUIC stream (uses a hash table to track this)
quicmux
- Multiplex QUIC streams and datagrams on the same QUIC transport connection
- Adds meta to buffers to distinguish between stream and datagrams at the transport layer
- New stream (uni/bi-directional) or datagram connection is opened depending on the requested pad
- Buffers on stream pads don't map directly to frames at QUIC layer and are payloaded by the library.
- Uses custom query events for handling connections with
quicsinkdownstream
quicsrc
- Uses the meta on buffers to decide if the buffer is from a stream or datagram
Media over QUIC
- Optimised for QUIC protocol either directly or via WebTransport.
- Utilises a publish subscribe workflow
- Designed to work with multiple MoQ streaming formats which define how content is encoded, packaged and mapped to MOQT objects along with policies for discovery and subscription.
Terms
Group: a temporal sequence of objects. A group represents a join point in a track.
Track: an encoded bitstream. Tracks contain a sequential series of one or more groups and are the subscribable entity with MOQT.
Object: an object is an addressable unit whose payload is a sequence of bytes. Objects form the base element in MOQT model.
Objects
- Basic data element of MOQT is an object.
- An objects is an addressable unit whose payload is a sequence of bytes.
- All objects belong to a group (indicates ordering and potential dependencies)
- Uniquely identified by track namespace, track name, group and object ID.
- Can become unavailable but contents must not change over time.
- Comprises of metadata (never encrypted, visible to relays) and payload.
- Application alone responsible for content of object payload.
- Relay must not combine, split or otherwise modify object payloads.
Groups
- Collection of objects, sub-unit of track.
- Objects within groups shouldn't depend on objects in other groups.
- Behaves as joint point for subscriptions.
Track
- Sequence of groups.
- Entity against which a consumer issues a subscription request.
- Subscriber can request to receive individual tracks starting at group boundary.
Session initialisation
- First stream opened is a client initiated bi-directional control stream.
- Peers exchange setup messages on this stream.
- Control messages must not be sent on any other stream, if received on a non-control stream, it'll be a protocol violation.
- Control stream is the only bi-directional stream. Objects are sent on uni-directional streams. A second bi-directional stream would be a protocol violation.
- Objects are sent on uni-directional streams.
Stream cancellation
- Streams aside from the control stream may be cancelled due to congestion or any other reason.
Termination
The transport session can be terminated at any point.
WARP
- WARP streaming format is a media format designed to deliver CMAF compliant media content over MOQT.
- Fragments the bitstream into objects that can be independently transmitted.
- Uses a prioritisation strategy of assigning newer content a higher delivery order and video over audio when facing congestion.
- Either complete GOPS or individual frames are mapped to MoQTransport objects.
- Targeted at interactive levels of latency.
Time alignment
WARP tracks may be time aligned. (Don't understand this here)
- Time aligned tracks must be advertised in the catalogue as belonging to a common render group.
- Presentation time of the first media sample contained within the first MOQT object of each equally numbered MOQT group must be identical.
Media transmission
MOQT groups and objects need to be mapped to MOQ transport streams. Each MOQT object must be mapped to a new moq-transport stream.