Abstract: A computer-implemented method includes receiving an encoded video input file comprising a plurality of video frames arranged in a timeline, receiving one or more video artifacts at respective time offsets along the timeline, generating a synthesized video stream based on the encoded video input file and the one or more video artifacts, and exporting the synthesized video stream into an encoded video output file. Generating the synthesized video stream includes identifying first and second segments of video frames along the timeline based at least in part on the time offsets of the one or more video artifacts, decoding the second segments of video frames, generating composite segments of video frames by combining the decoded second segments of video frames with corresponding video artifacts, encoding the composite segments of video frames, and concatenating the first segments of video frames and the encoded composite segments of video frames along the timeline.