1. A broadcast receiver comprising: a first video signal selector which receives a plurality of input video signals and outputs any of the plurality of input video signals as a video signal of a main-picture; a second video signal selector which receives the plurality of input video signals and outputs any of the plurality of video signals as a video signal of a sub-picture; a first audio signal selector which receives a plurality of input audio signals and outputs any of the plurality of input audio signals as an audio signal of the main-picture; a second audio signal selector which receives the plurality of input audio signals and outputs any of the plurality of input audio signals as an audio signal of the sub-picture; a first video processor which generates a third video signal by using at least one of the video signal of the main-picture output from the first video signal selector and the video signal of the sub-picture output from the second video signal selector; a feature quantity generator which generates a feature quantity of the audio signal of the sub-picture output from the second audio signal selector in accordance with a result of comparison between data corresponding to the audio signal of the sub-picture and sound class model data created beforehand in accordance with collected known scenes; a determination processor which determines a scene as a specified scene when the feature quantity exceeds a predetermined threshold; and a controller which controls the first video signal selector, the second video signal selector, the first audio signal selector, the second audio signal selector, and the first video processor, in accordance with the specified scene detected by the determination processor.