Historically it has not been possible to live stream h264, but I have not rechecked the latest two releases. I cannot presently rule out the possibility that a recent change to support for one of the boards such as arduino might perhaps have added the capability; it was not there in R2017a (not without running a custom adapter)
Devices such as gigabit cameras return entire frames in the mode supported by MATLAB, rather retuning h264 streams with some hypothetical function to decode the frames.
The historical support for h264 has only been from file, not streaming.
If you have Windows then you can use activexserver to talk to a COM object to do the decoding for you and to return the frames.