codec for mjpeg. the goal is to make a frame by frame iterator There is no standard specs for MJPEG.
References: https://sites.ualberta.ca/dept/chemeng/AIX-43/share/man/info/C/a_doc_lib/ultimdia/ultiprgd/MJPEG.htm
"MJPEG is based on the mature compression standard i.e. JPEG that has well-defined libraries. It could not be standardized similar to standards such as MPEG-2 and there is no documentation available that can be referred to as complete specifications for the “Motion JPEG”. In the absence of such a standard, outputs from different manufacturers can raise compatibility issues. However, companies like Microsoft and Apple have documented how the M-JPEG files are stored in their native formats such as AVI and QT. The rfc2435 describes the RTP Payload Format for JPEG-compressed Video and can be consulted as reference material." https://docs.fileformat.com/video/mjpeg/
https://learn.microsoft.com/en-us/windows/win32/directshow/avi-riff-file-reference