We are having a firewall issue and have identified it as a MTU problem. vMix is sending SRT packets out with an MTU of 1374. When these packets hit a firewall of any kind the packets break up and we lose the video. Sending SRT between computers behind the firewalls works perfectly. Looping the same SRT stream through FFMPEG and dropping the pkt_size to 1128 fixes the issue nicely. With the pkt_size at 1128, we end up with an MTU of 1186 and we are good to go.

Here is the question:
How to we change pkt_size from the default of 1316 to 1128 within vMix? I can't find a setting for this.

Thanks for your time.
Rick