Dynamic Metadata for Media Content Delivery

Systems and methods for providing estimates of duration of media content requested by a user are disclosed. The estimates of the duration may be updated as advertisements are identified and/or updated for insertion in media content signals to be provided to a client device of the user. The advertisements may be targeted to the user from an inventory of available advertisements based on a variety of factors. While a session is active to provide the client device with the user requested media content new duration estimates corresponding to updates to advertisements targeted for delivery to the user may be provided to the client device via messages and/or metadata. In some cases, this information may be provided by messages sent responsive to a trick play request form the client device. In other cases, an asynchronous message carrying updated duration information may be sent to the client device.