9. Apparatus for multimedia content generation, comprising: an interface for communicating over a communication network; and a processor, which is configured to receive a textual input, to estimate, before receiving an audio narration of the textual input, occurrence times of respective components of the audio narration, to automatically retrieve, from one or more media databases over the communication network, a plurality of media items that are relevant to the textual input, to receive user input, which selects one or more of the automatically-retrieved media items and correlates one or more of the selected media items in time with the textual input, to receive an audio narration of the textual input, and to automatically construct a video clip, which comprises the audio narration and the selected media items scheduled in accordance with the user input, by scheduling the selected media items in accordance with the estimated occurrence times.
9. Apparatus for multimedia content generation, comprising: an interface for communicating over a communication network; and a processor, which is configured to receive a textual input, to estimate, before receiving an audio narration of the textual input, occurrence times of respective components of the audio narration, to automatically retrieve, from one or more media databases over the communication network, a plurality of media items that are relevant to the textual input, to receive user input, which selects one or more of the automatically-retrieved media items and correlates one or more of the selected media items in time with the textual input, to receive an audio narration of the textual input, and to automatically construct a video clip, which comprises the audio narration and the selected media items scheduled in accordance with the user input, by scheduling the selected media items in accordance with the estimated occurrence times. 14. The apparatus according to claim 9 , wherein the processor is configured to define multiple scheduling permutations of the selected media items, to assign respective scores to the scheduling permutations, and to schedule the selected media items in the video clip in accordance with a scheduling permutation having a best score.