Among multiple services delivered over future mobile networks, the most demanding (from the required bandwidth point of view) are related to media streaming, which is a key component in smart applications (entertainment, tourism, surveillance, etc.). Such applications have to exploit a considerable amount of data, which is difficult to achieve especially in dense urban environments. In this context, the article presents a new solution for HTTP-compliant adaptive media streaming applicable to future 5G mobile networks, aimed at increasing bandwidth availability through the use of multiple radio access technologies and direct connections between devices if they are in proximity of each other. The proposed solution considers a scenario in which a high-quality media stream is received by multipath transmission through the radio access network. Collaboration of neighboring devices is exploited by using direct device-to-device links. Thus, proxy nodes can be inserted between a given media receiver and an access network. Toward ensuring optimized resource allocation at both levels, base station-to-device and device-to-device, this article introduces the architectural modules required for collaboration streaming inside the radio access network and end user's device, and proposes enhancements in HTTP-compliant adaptive streaming protocols in order to become suitable for a multipath collaborative scenario.