YouTube’s standard aspect ratio is 16:9. If your video is set to a different aspect ratio (e.g., if you forgot to rotate your phone sideways when recording), it will appear with black bars on the sides and/or top and bottom of the frame.
YouTube recommends uploading videos in the same frame rate that they were recorded. Popular frame rates include 24, 25, 30, 48, 50, and 60 frames per second. Faster frame rates create smoother, clearer looking videos.
Video container is another term for the file format. YouTube recommends using MP4 as your video container but supports multiple formats.
Your video codec encodes your video’s data stream, which means it governs how much quality loss occurs in file compression. The best video codec for YouTube is H.264.
Like your video codec, your audio codec governs the audio quality that may be lost due to compression. YouTube recommends AAC-LC.