Embodiments of the present invention provide a system, a terminal, and a method for dynamically adjusting a video. The system includes: a session control unit, configured to: in a video playing process, receive operation control signaling sent by a user proxy, and generate a transcoding instruction according to the operation control signaling, where the transcoding instruction includes an updated transcoding parameter; and a transcoding unit, configured to receive the transcoding instruction sent by a session control unit, transcode, according to the updated transcoding parameter, an original video image received from a video source so as to generate a transcoded video image, and send the transcoded video image to the user proxy.