As Google notes, «Gaining code execution in libstagefright previously granted access to all the permissions and resources available to the monolithic mediaserver process including graphics driver, camera driver, or sockets, which present a rich kernel attack surface. (androidauthority.com)
This kind of separation means that any future vulnerabilities would be confined to a much smaller part of the system rather than the whole mediaserver gamut. (androidauthority.com)
Google also said it's updated its Hangouts and Messenger apps so that they don't automatically process video messages in the background «so that media is not automatically passed to mediaserver process.» (androidcentral.com)