If you don't have a bit rate limit set at all, then
Blue Iris can encode obscenely high bit rates that not all decoders can handle. This is especially true if you have increased the H.264 quality setting from its default of 50%. Blue Iris uses a different quality scale than most apps, where 50% is really high quality already. Lots of people don't realize this so they set the encoding quality to 90 or 100%, undermining any hope the encoder had of being efficient.