Complex sentence: Standard definition video can be recorded in 4:3 and 16:9 formats, but the latter is not correctly identified in media file header, so video may appear squeezed horizontally when viewed.
Split into simpler sentences: Standard definition video can be recorded in 4:3 and 16:9 formats. Some video decoders do not interpret the aspect ratio information in the media file header correctly, so 16:9 video may appear squeezed horizontally when viewed.