These are the kind of things that make video decoding work for a particular codec, such as the current set of reference frames, the current position in the bitstream, whether any special decoding mode is enabled for the current frame and its current length, and also compression-specific metadata, if any. v4l2codecs consists of classes to abstract key kernel ioctls for dealing request and buffer management, wrapping them into GStreamer objects that can be used by GStreamer decoders when processing a given bitstream.