Hello Jakub.
Welcome to the Hub.
Yes, you are correct. AVB is using MSRP(Multiple Stream Reservation Protocol).This technology ensures audio and video can leverage a predefined amount of the bandwidth for AVB audio. This amount is 75% of the maximum data rate; the other 25% of bandwidth can be used for other data. (Note: These percentage allocations can be adjusted as required across all Extreme Networks AVB-enabled switches.)
If you used Summit x440-24, sorry you cannot configure the bandwidth.
If you had G2 product, such as, x460-G2, you could change the bandwidth by using "configure msrp ports traffic-class delta-bandwidth"
http://documentation.extremenetworks.com/exos_commands_22.2/exos_21_1/exos_commands_all/r_configure-...
Best regards,