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Various use cases for codec negotiation
=======================================
One-to-one
----------
Starting with an offer
- Create session
- Possibly set the codec-preferences
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get list of codecs
- Get codecs from FsSession and send them
- Wait for reply
- Set remote codecs on FsStream
Replying to an offer
- Create session
- Possibly set codec-preferences
- Set remote codecs
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get list of codecs
- Send reply
Creating a new offer
- Possibly set codec-preferences
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get codecs from FsSession and send them
- Wait for reply
- Set remote codecs on FsStream
Replying to a re-offer
- Set remote codecs
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get list of codecs from FsSession
- Send reply
Multi-party
-----------
First, it starts with a single party call
The conference master invites someone in a call
- Possibly set codec-preferences
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get codecs from FsSession and send them
- Wait for reply
- Set remote codecs on FsStream
Someone asks the master to join a call
- Set remote codecs
- While codecs-ready property is false
- wait until the codecs-changed message is emitted
- Get list of codecs from FsSession
- Get list of codecs from every other stream
- Send reply with master codecs and codecs from every other stream
- .. Or just get list of codecs from everyone (if using a presence based system)
Goals
=====
- Negotiated codecs should never change ids (or become incompatible)
- In one-to-one, we should always prefer the remote codec id & params
- In one-to-many, we should prefer our codec id and param
- We have to keep a copy of the local and remote config-data
- We have to produce list of codecs with the local and remote config-data
- We must be able to extract config-data-less codecs for multicast/sip,
but we must also be able to produce them with the config data for cooler ones
How negotiation works now
=========================
(I'M NOT CERTAIN THIS IS ACCURATE...)
validate shall remove all config-data from preferred codecs
the whole thing is ran whenever one of the parameters change (remote codecs, local codecs, local codecs config)
out: codecs_with_config, codecs_without_config, new codecs in streams
in: codec_preferences, blueprints, remote_streams with each its codecs,
codecs_with_config
FsCodec gets a list of config_data that is filled from optional_params by
the codec specific negotiation function from the optional params of the local codec or the remote codec.
CodecAssociation gets a two new markers.. one is "need-config" and the other is "recv-only".. Need-config means that we have to try to fetch config-data, "recv-only" means it should only be used by the list in the stream, not in the public list. There should also be a marker for "empty" associations
create empty list of codec assocs
foreach codec_preference:
if its a disable-codec entry:
ignore it
else if its a "reserve-pt":
add a "reserve-pt" marker to the the list
else if there is a matching codec in the old codecs (is a sdp negotiable
codec) with the same id:
add it to the list with the id from the old codecs
else if there is a matching blueprint:
add the codec to the list with new id (not in already in existing list or
preferred list or new list)
foreach codec:
if there is no pt number:
attribute an allocated pt number to it
foreach codec blueprint:
if there is no matching codec already in the list
if its not marked as disabled
add a codec to the list with id from already existing codecs or find new
id (not in already existing list or new list)
Now we have a list of "local codecs"
foreach stream that has remote codecs:
create empty new_list
foreach remote_codec:
check if there is an existing assoc (in the list of "local codecs") in the
list with the same id that matches or if there is a codec in the list that
matches:
add this code_assoc to the new_list with remote id if there is only one
stream with codecs, otherwise take the local id
else
add id to list of known ids and process next codec
replace list with new_list
if the new list is empty:
return failure
Now we have the general codec intersection
# for Tandberg and such that don't do SDP Offer-Answer properly
foreach codec in the incoming list:
if there is no codec with the same id in the new list:
add the codec from the original list to the new list with a marker (and without config data)
foreach id in the list of known ids:
if there is nothing in the codec list:
add a marker to the codec list
# Distribute the codecs to each stream
foreach stream that has remote codecs:
create an empty list
foreach negotiated codec (includes the one with a marker):
check if there is a codec with the same id in the remote codecs
if none found:
check if there is a remote codec that matches
add the codec with the remote codec config data to the list (possibly copying the marker)
replace the list of remote codecs in the stream with the newly created list
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