For almost all compression algorithms (both lossless and lossy), only the decompression is specified. A compressor can do whatever it wants as long as it produc

For almost all compression algorithms (both lossless and lossy), only the decompression is specified. A compressor can do whatever it wants as long as it produces a bitstream that a compliant decompressor can decode. For example, you can make a video enocoder that produces a compliant video stream in which every frame is a keyframe and every macroblock is independently fully encoded, thus reducing AV1 (or H265, etc.) to MJPEG. But if the result is decodable by a compliant decoder, your compressor is compliant. It might even be somewhat useful (e.g. output needs to be zero latency or output is intended to be edited).