Jframe

A j-frame (also known as a j-type frame) is a type of frame similar to an i-frame used in microsofts mpeg4 variation codec WMV2 and the same coding method (with the different header) is used in WMV3 Complex Profile under the name "X8".

MPlayer on x86 can play files containing these frames using a binary codec. ffmpeg can also play files containing j-frames, but, those frames will be skipped. j-frames have not been reverse engineered, so there is no documentation available. If a stream contains j-type frames the j-type bit will be set in the streams extradata.

The main differences between j-frames and i-frames:

1. They are not derived from MPEG-4 standard
2. Picture is coded as blocks, not as macroblocks
3. Each frame may use its own Huffman codes