Using FlowCaster with Avid MediaComposer

FlowCaster SwirlFlowCaster creates an Open I/O board Avid creative software like MediaComposer.  As a virutal video board, it can send the same high quality audio, video and captions from a real or virtual machine to wherever you are doing your creative work for output on a 'third monitor'.  This signal can be recieved by free software, like VLC and the HaiVision Pro Player, or by dedicated Drastic recievers for more features, like FlowCaster for IOS and Android, videoQC for Windows, macOS and Linux or even a variety of hardware decoders from Aja, HaiVision and others.  This article demonstrates configuring FlowCaster in Avid MediaComposer.


Avid MediaComposer

 To configure FlowCaster in Avid MediaComposer, you first have to enable it on the timeline.  Find the Open IO output button just above the timeline

FlowCaster Avid OpenIOButton

To enable it, right click on it and select FlowCaster.  If FlowCaster is already selected, you can just left click on the button. 

FlowCaster Avid OpenIOButton Menu

Once enabled, the button will flash a red double arrow to indicate it is sending to FlowCaster.

FlowCaster Avid OpenIOButtonEnabled

When enabled, a new manu under Tools will be available called Video Output Tool

FlowCaster Avid VideoOutputTool Menu

Click on this will bring up the Flowcaster Configuration Dialog

FlowCaster Configuration Dialog

FlowCaster Config Dialog

Transmit Type

SRT Caller - this uses SRT to call our to a remote device.  The IP and port for this protocol in URL should be the remote device's IP address and selected port

SRT Listener - this uses SRT to listen on your local machine.  The IP must be one of the IPs on you machine, and you must select a port to recieve on

SRT Rendezvous - this mode uses the external, internet IP to connect through local NAT routers.  Here is should be the internet facing IP of the remove device.  On that devices config, it should be your internet facing remote IP.  To get those IPs, from each network, use https://whatismyipaddress.com/

RTP - the IP and Port for this mode can be the remote device, or a multicast address (239.x.x.x) that both the sender and reciever are set to

UDP - the IP and Port for this mode can be the remote device, or a multicast address (239.x.x.x) that both the sender and reciever are set to

RTMP - the URL for this mode will consist of the remote server, followed by the remote key   For instance, with YouTube.com, the address would be rtmp://a.rtmp.youtube.com/live2, and the key would be provided by YouTube and look something like this j2br-3t45-b6ck-s9h9-5dcy, so the URL would be rtmp://a.rtmp.youtube.com/live2/j2br-3t45-b6ck-s9h9-5dcy

NDI - for NDI, the URL would be a unique name, that NDI will combine with the computer name, to create a fully qualified name you can use to connect to the stream


Normally the IP and Port or a fully qualified URL, depending on the Transmit Type setting.  Below are some typical examples

SRT Caller:

SRT Listener:

SRT Rendezvous:



RTMP:  rtmp://a.rtmp.youtube.com/live2/j2br-3t45-b6ck-s9h9-5dcy

NDI:  FlowCaster1Out


Latency is the number of milliseconds to give the signal to recover packets.  This is for SRT.  The lower this number, the closer to real time the monitor will be.  The larger, the more room it will have to recover any lost packets.  It is recommended this be the RTT (round trip time) between the two devices plus 20 milliseconds


SRT supportes end to end encryption.  Settting this to 128 or 256 will cause all the data to be encrypted, use the Password below.


If encyption above is set to 128 or 256, then this password will be used to encypt the signal, and it must be used on the recieving device for it to be able to decrypt the signal


If your protocol/transmit type require authentication, this is the user name that will be used in that authentication

Stream #

If your protocol/transmit type supports multiple stream sets, this will specify which one you are sending


What compression to use to send the stream.  FlowCaster supports h.264, h.265/HEVC and JPEG 2000, but the reciever must also support them for the monitor to work.  If you are unable to see the signal in the reciever, start with h.264 8 bit 4:2:0 and then work up from there to see what the receiver supports.  videoQC supports all the codecs.


This is the internal structure of the compression.  Three modes are supported

  • IBBP - this has the highest quality, but the longest latency
  • IPPP - this has the best compromise between quality and latency
  • IIII - this as the shortest latency, but the worst quality

Bit Rate

The kilobit rate to encode the video within.  For instance, 2 mbs (megabits) would be 2000 kbs (kilobits)

Reciever Supports HDR Signalling

If your recieving software supports HDR Signalling, checking the checkbox will enable sending any local HDR signalling to the remote monitor

Audio Mode

FlowCaster supports 5 audio modes

  • Stereo - just the first stereo pair
  • Stereo Mix - mix all available channels to a stereo pair
  • 4 channels - send the first four channels
  • 8 channels - send the first eight channels
  • 16 channels - send the first sixteen channels


A path and filename to a file to place on the output as a watermark.  This would normally be a 32 bit PNG file with Alpha.  The "..." button will bring up a file browse dialog to allow you to select a file from your local file system.  The two numbers separated by a comma and the x and y start position of the watermark on the output signal in pixels.


Once the OK button is clicked, FlowCaster will reset its output to match the new setup.  This may take a few seconds before you see the changes on the reciever.


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