- Stream from camera, cropped vertically (portrait)
- Stream from desktop/display/window (desktop might be multiple displays; might need to share multiple windows)
- Scaled down stream for all participants
- Scaled up stream for talking participants
- Two talking participants side-by-side with upscaled stream
- Audio mixer&autolevel (avoid leveling background noise up)
- Warn “you are muted” if you talk while being muted
- Hotkey to turn audio and video on/off
- Display FFT of audio for visualisation
- Audio biquad filters, e.g. notch, to improve bad sound quality
- Push to talk, hotkeys for everything
- Hotkey for cut mark + keyframe
- Local recording with higher res/audio quality for presenter
- Allow multiple devices (cameras, mics) for one participant (Akira Kurosawa
setup), no own audio in backchannel
- Bonus points if multiple participants in the same room can be identified (e.g. send a short chirp out, and check for it in other audio streams)
- room microphone mode — device does not receive audio or video, and can send audio only in push-to-talk mode.
- Templates for nice presentation recording
- Set a logo for the talk
- Have a countdown clock for talk slots
- Share slides directly (slides in Markdown)
- Subtitles as option for slides (possibly multiple languages)
- Translated audio tracks to select from (for bigger conferences)
- Rooms for small-group side conversation
- Moderator side channel to presenter/participants
- Try connections to different participants and take best one
- Mix additional audio sources (background music, desktop sounds, claps/laughers)
- Spatial audio (different participants from different directions)
These are “nice to have” features with some caveats.
- Recognize eyes and move them upwards so that it looks like the participant is looking at you (instead of downwards)
While the network itself is peer to peer, the roles in a video conference have a central point, the moderator. The moderator collects the streams that are created at the endpoints, mixes them, and distributes the result to everybody.
This is easy when the central instance is a well connected server. With a p2p network, you have to distribute the load of both collecting the data and distributing it, but the central point of control (the moderator) remains.
net2o's basic paradigm is that of storage objects, so every object (file) has a hash, and sending participants can authenticate objects with a signature. Life streaming however means new information is added on the fly.
Participants send metadata information on every update: (size, hash) for every object, and a signature for all objects.
A complete video stream consists of several objects:
- Audio index (one index block per second, one data size per packet)
- Audio data (Opus encoded data)
- Video index (one index block per second, one data size per packet)
- Video data (h.264/h.265/vp8/vp9/av1 depending on what's available for the hardware encoder)
- Metadata index (timestamp:type:size)
- Metadata (thumbnails as small images, subtitles as text, shared slides as files)
Video data encoding depends on what's available as hardware encoder with the participants.
Tradeoffs: Software video encoders have good quality, but are slow. Hardware encoders have lower quality, but are fast and don’t consume much power.
Life streaming requires real–time distribution of data from one to many participants. net2o uses an avalanche tree distribution for streaming: Data stream blocks are partitioned. Each partition is send to a tree of nodes. The branch nodes send it forward to further nodes. The leaf nodes send it forward to nodes from other partitions. This makes sure that every node has the same load.
The dangling edges that point nowhere show that it is possible to add one further node to this tree at any point in time. The tree allows to have low–latency streaming to many participants. The fanout here is four; in reality, it can be significantly bigger.
For timeshift streaming alone, a much simpler relation is possible: an ordinary queue. Every watcher starts by being added to the tail of the queue, watching the video stream right from start. It takes that stream from the one next in the queue, which got it recently. If the delay between two participants becomes too small for that simple queue, the real–time streaming tree concept can be used for them.
Timeshift streaming watchers who skip over parts have to change the position in the queue. Since they then don’t have the entire video, they can‘t distribute all of it. Everybody still can contribute as much as he consumes, it is still a fair share.
Collection tree and mixing
Each active node in a video conference creates a stream of data. Mixing the data is distributed; sending it directly to one central instance will easily overwealm that one.
- Leaf nodes send their stream upwards. Audio is processed by applying filter, volume control and spatial audio at the leaf, video streams are truncated and scaled down as necessary.
- Participants can offer their own stream as life stream for others to join, but other nodes will only select one or two life streams
- Branch nodes combine leaf node streams and own stream to mixed stream
- Audio is just mixed together
- Video is stiched together (if possible without transcoding, see for example this paper using HEVC for stitching videos together)
- Rogue participants ignoring commands are muted either here or if the entire branch is rogue, at the root
- Root node combines final downmix, and distribute that as life stream
- Every participant has one single upstream
- Branch nodes have multiple downstreams (asymmetric subscriber lines work well here)
- Every participant handles a fair share of the central stream distribution
- Every participant needs to encode one stream + local copies of the own recording
- Every participant needs to decode more than one stream
- The instructions how to downscale and mix the incoming streams come from the moderator node
The own recording is available afterwards for remixing the entire conference with higher quality, or in case connection losses took out participants and people want to check what they missed.