View source for Contributions:AVMeetingExtension

==Synopsis==
This extension displays video from a remote location, plus local video in a user application window.
It works in conjunction with the ''SimpleRelayServer'' application running within a local network, or on the internet.
Audio may be transferred in one direction as well. Bidirectional audio is possible but will lead to feedback unless earphones are used.

===Authors===
Jürgen Mellinger (mellinger@neurotechcenter.org)

==SimpleRelayServer==
To allow connection between machines across local networks at different locations, it is necessary to 
run a relay server located somewhere in the open internet, on a Linux server under the experimenter's control.

Follow these steps to build and run the necessary ''SimpleRelayServer'' executable on a Linux machine:
* Download <tt>SimpleRelayServer.cpp</tt> from
https://bci2000.org/svn/trunk/src/contrib/Extensions/AVMeetingExtension/SimpleRelayServer/SimpleRelayServer.cpp
* cd to the download's directory and execute
 g++ SimpleRelayServer.cpp -o SimpleRelayServer
* Start the server with
 ./SimpleRelayServer 2>/dev/null
or just
 ./SimpleRelayServer 
if you want to see log messages on the console.
By default, the server process will listen on all of the machine's interfaces, at port 1915.
A different port may be specified by providing a command line argument:
 ./SimpleRelayServer 1928 2>/dev/null

==Parameters==
===EnableAVMeeting===
If nonzero, enables the AVMeeting extension.

===StreamingServer=== 
The streaming server's address with port, as in ''upload.bci2000.org:1915''. This must match the ''SimpleRelayServer's'' listening address.
For testing purposes, an instance of the streaming server is running at the BCI2000 server's address given above.

===CameraIndex===
The local camera's 0-based index into the video backend's list of detected cameras. Typically 0 unless multiple cameras are attached.
A value of -1 disables video streaming.

===AudioDeviceIndex===
The local audio input device's 0-based index into the audio backend's list of detected audio devices.
Specify -1 to disable audio streaming from the local machine.

===VideoEncoder===
The name of the desired video encoder to use, e.g. h264_mf or libx264.
Specify ''auto'' to use h264_mf on Windows, and libx264 on non-Windows systems.

===RemoteVideoRect===
The display rectangle for remote video, in relative coordinates. Values are ''left'', ''top'', ''bottom'', ''right''. Defaults to <tt>0 0 1 1</tt>, i.e. the entire window.

===RemoteVideoZ===
The remote video display's Z coordinate. Objects with a smaller Z coordinate are displayed on top objects with larger Z coordinates.

===RemoteVideoVisibility===
A BCI2000 expression which may entail BCI2000 state names. Whenever this expression evaluates to a nonzero value, remote video is displayed.
Otherwise, remote video is hidden.

===LocalVideoRect===
The display rectangle for local video, in relative coordinates. Values are ''left'', ''top'', ''bottom'', ''right''. Defaults to <tt>0.75 0 1 0.25</tt>, i.e. the upper right corner of the display window.

===LocalVideoZ===
The local video display's Z coordinate. Objects with a smaller Z coordinate are displayed on top objects with larger Z coordinates.

Note that by default the local video rectangle overlaps with the remote video rectangle, and local video is on top of the remote.

===LocalVideoVisibility===
A BCI2000 expression which may entail BCI2000 state names. Whenever this expression evaluates to a nonzero value, local video is displayed.
Otherwise, local video is hidden.

==States==

===VideoStreamingLocalTotalFrames===
A 32-bit state holding the current local frame number since the beginning of the current recording (BCI2000 run).

===VideoStreamingRemoteTotalFrames===
A 32-bit state holding the current remote frame number since the beginning of the current recording (BCI2000 run).

===VideoStreamingLocalFrame===
A 32-bit state holding the current local frame number since the beginning of the current file.

===VideoStreamingRemoteFrame===
A 32-bit state holding the current remote frame number since the beginning of the current file.

==Files==
Both local and remote video is being recorded into files in mp4 format.
These files bear the current BCI2000 file's basename, followed with <tt>_VideoStreamingLocal</tt> and
<tt>_VideoStreamingRemote</tt>, respectively.

'''NOTE:''' Seeking to individual frames is not possible for mp4 files unless frame time stamps exactly match the frame rate specified at the beginning of the file. To work around this, video files are created with the camera's nominal frame rate, and artificial time stamps proportional to frame number are used when writing frames to a file.
In analysis, it will be possible to reconstruct actual time stamps using one of the frame count states.

However, replaying mp4 files written by the ''AVMeetingExtension'' with a standard video player may not result in proper playback speed.

==See also==
[[Contributions:Extensions]]

[[Category:Contributions]]