The code for populating the shm buffer from the parameters to addSegment() will be common on the client & server side so this should be stored in a common location to be used by both implementations.

@startuml

autonumber

box "Platform" #LightGreen
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server
participant Ocdm
end box

note across
Gstreamer app source uses 2 signals, need-data and enough-data,
to notify its client whether it needs more data. Rialto server
should only push data when the appsrc indicates that it is in
the need-data state.
end note


loop While appsrc needs data && appsrc data available in shm buffer

rialtoServer       ->  rialtoServer:      Extract frame's metadata from shm
opt Frame encrypted

rialtoServer	   ->  GStreamer_server:  gst_buffer_add_protection_meta(buffer, meta)

end

rialtoServer       ->  GStreamer_server:  Set width/height caps
opt new codec_data in frame
rialtoServer       ->  GStreamer_server:  Set codec_data caps
end

rialtoServer       ->  GStreamer_server:  gst_app_src_push_buffer(src, gst_buffer)
rialtoServer       ->  rialtoServer:      'Remove' frame from shm

opt First video frame pushed at start of playback / after seek
note across: Not currently implemented

@startuml

autonumber

box "Platform" #LightGreen
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server
participant Ocdm
end box

note across
Gstreamer app source uses 2 signals, need-data and enough-data,
to notify its client whether it needs more data. Rialto server
should only push data when the appsrc indicates that it is in
the need-data state.
end note


loop While appsrc needs data && appsrc data available in shm buffer

rialtoServer       ->  rialtoServer:      Extract frame's metadata from shm
opt Frame encrypted

rialtoServer	--/ rialtoClient:      notifyFrameReady(frame_timestamp)
end

opt Appsrc data exhausted from shm
opt (status == EOS) for this appsrc
rialtoServer       ->   GStreamerGStreamer_server:    gst_buffer_add_protection_meta(buffer, meta)

end
  notify EOS
else Not EOS
rialtoServer       ->  GStreamer_server:  Set width/height caps
opt new codec_data in frame
rialtoServer    --/ rialtoClient:      notifyNeedMediaData(...)
end
end

end

@enduml

@startuml

autonumber

box "Platform" #LightGreen
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server
participant Ocdm
end box

GStreamer_server   ->  GStreamer_serverrialtoServer:    Set codec_data caps
end decrypt(buffer)

rialtoServer  	     ->  GStreamer GStreamer_server:  gst_appbuffer_srcget_pushprotection_meta(buffer(src, gst_buffer)
)
 
opt Protection Meta exists (Frame encrypted)
 
rialtoServer       ->  rialtoServer:      'Remove'Extract frame's from shmmetadata

opt First video frame pushed at start of playback / after seek
note across: Not currently implemented
rialtoServermedia_keys.key_system == "com.netflix.playready"
rialtoServer       ->  Ocdm:       --/ rialtoClient:      notifyFrameReady(frame_timestampopencdm_select_key_id(ocdm_session, kid)
end


opt AppsrcImplementation databefore exhaustedCBCS fromsupport shm
opt (status == EOS) for this appsrc
rialtoServeradded
rialtoServer       ->  Ocdm:              ->  GStreamer_server:      notify EOS
else Not EOSopencdm_gstreamer_session_decrypt_ex(ocdm_session, gst_buffer, subsample_info, iv, key, init_with_last_15, caps)
else Implementation after CBCS support added
rialtoServer       --/>  rialtoClientOcdm:            notifyNeedMediaData(...)
end   opencdm_gstreamer_session_decrypt_buffer(ocdm_session, gst_buffer, caps)
end

end

@enduml

@startuml

autonumber

box "Container" #LightGreen
participant Cobalt
participant Starboard
participant GStreamer_client: notifyPosition(pipeline_session, position)
note over GStreamer_client: Not used by Cobalt as some conformance\ntests require very high position accuracy


== Get position ==

Cobalt    
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server
end box

opt End of content reached
GStreamer_server   -/  rialtoServer:         GST_MESSAGE_EOS
rialtoServer       ->/  StarboardrialtoClient:         SbPlayerGetInfo2(player)
Starboard notifyPlaybackState(pipeline_session, END_OF_STREAM)
rialtoClient       ->/  GStreamer_client: Get position    notifyPlaybackState(pipeline_session, END_OF_STREAM)
note left
This should notify all attached sinks of EOS
end note
GStreamer_client   ->/  rialtoClientStarboard:     getPosition(pipeline_session)
rialtoClient     ->  rialtoServer:GST_MESSAGE_EOS
Starboard     getPosition(pipeline_session)
rialtoServer     ->/  GStreamer_serverCobalt: Get position from pipeline
GStreamer_server --> rialtoServer:     position
rialtoServer    PlayerStatus(player, kSbPlayerStateEndOfStream)
end

@enduml

@startuml

autonumber

box "Container" #LightGreen
participant Cobalt
participant Starboard
participant GStreamer_client
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server
end box

== Initialisation - register for callbacks ==

opt Video source attached
rialtoServer --> rialtoClient:     position
rialtoClient     --> GStreamer_client: position
GStreamer_client --> Starboard:        position
Starboard        ->  StarboardGStreamer_server:     g_signal_connect(video_decoder, getVideoUnderflowSignalName_soc(),  Set player_info.pos = position
Starboard        video_underflow_cb, user_data);
GStreamer_server   --> CobaltrialtoServer:           player_info

@enduml

@startuml

autonumber

box "Container" #LightGreen
participant Application
participant rialtoGstreamer
participant rialtoClient
end box

box "Platform" #LightBlue
participant rialtoServer
participant GStreamer_server 
end box

== Decryption ==
GStreamer_server   -->  rialtoServer:
end

opt Audio source removed
rialtoServer          decrypt(buffer)

rialtoServer	   ->  GStreamer_server:  MediaKeyErrorStatus::Fail
GStreamer_server   ->  GStreamer_server:     g_signal_handler_disconnect(audio_decoder, audio_handler_id);
GStreamer_server   --> rialtoServer:
end


== Underflow ==

opt Data starvation in server AV pipelineGST_BASE_TRANSFORM_FLOW_DROPPED 

note over GStreamer_server
Frame is dropped but playback is unaffected.
end note 

GStreamer_server   -/>  rialtoServer:         video_underflow_cb() or audio_underflow_cb()GST_MESSAGE_WARNING(src, GST_STREAM_ERROR_DECRYPT)

rialtoServer          -/  rialtoClient rialtoClient:         notifyBufferUnderflow(source_id notifyPlaybackError(MediaSourceType, PlaybackError::DECRYPTION)
rialtoClient       -/  GStreamer_client:     notifyBufferUnderflow(source_id)
GStreamer_client   -/  Starboard:            emit video_underflow_cb() or audio_underflow_cb()
 rialtoGstreamer:   notifyPlaybackError(MediaSourceType, PlaybackError::DECRYPTION)
 
note over Starboard, GStreamer_client
Starboard does not have any support for underflow
so the event can be ignored for this integrationrialtoGstreamer
Posting an error message on the sink make the\n
sink unable to continue playing back content.
end note

note across
There will be
rialtoGstreamer one re more pending-/ need Application: data  requests  at this point which if serviced will allow playback to resume
end note

end  GST_MESSAGE_ERROR(sink, GST_STREAM_ERROR_DECRYPT)

@enduml