Select a true Full HD 1080p source stream
For adaptive DASH playback, the 1080p video and audio can be separate downloads. The server retrieves the selected format IDs and muxes compatible tracks with FFmpeg, usually by stream copy; this places the encoded streams in one file without re-encoding the picture. Container and codec support still matter: H.264/AAC MP4 is broadly compatible, while VP9 and AV1 playback depends on the device. 1080p60 contains more frames and data than 1080p30, so file size and transfer time may differ substantially even at the same resolution.
1080p describes a frame with 1,080 vertical pixels; it does not by itself specify codec, frame rate, or bitrate. YouTube may expose Full HD as an H.264/AVC MP4 stream, a VP9 WebM stream, or multiple representations, and 60fps is available only when the source publishes it. YTMetadata lists the resolutions it can identify for the video, rather than upscaling 720p or fabricating a higher frame rate. The selected video track remains encoded as supplied unless a requested format requires conversion.