Author: michael Date: Sat Feb 2 22:11:18 2008 New Revision: 571 Log: The match_time_delta patch. Modified: docs/nut.txt Modified: docs/nut.txt ============================================================================== --- docs/nut.txt (original) +++ docs/nut.txt Sat Feb 2 22:11:18 2008 @@ -1,5 +1,5 @@ ================================== -NUT Open Container Format 20061104 +NUT Open Container Format 20080202 ================================== @@ -53,15 +53,20 @@ SHOULD It is recommended to be done tha keyframe A keyframe is a frame from which you can start decoding, a more exact definition is below - The nth frame is a keyframe if and only if frames n, n+1, ... in - presentation order (that are all frames with a pts >= frame[n].pts) can - be decoded successfully without reference to frames prior n in storage - order (that are all frames with a dts < frame[n].dts). - If no such frames exist (for example due to using overlapped transforms - like the MDCT in an audio codec), then the definition shall be extended - by dropping n out of the set of frames which must be decodable, if this - is still insufficient then n+1 shall be dropped, and so on until there is - a keyframe. + + A frame in a stream is a keyframe if and only if all of the following are true + * Decoding can successfully begin using any standard compliant decoder without + requireing access to prior frames. + * Begining decoding instead at a subsequent frame would cause fewer frames + to be decoded successfully. + + successfull decoding here means that the specific frame is virtually + identical to what one would get if decoding would have begun from the very + first frame + Note, "virtually identical" here is used instead of "identical" to allow + codecs which converge toward the same output when started from different + points but dont neccessarily ever reach exactly identical output. + Every frame which is marked as a keyframe MUST be a keyframe according to the definition above, a muxer MUST mark every frame it knows is a keyframe as such, a muxer SHOULD NOT analyze future frames to determine the @@ -314,6 +319,9 @@ frame: if(frame_flags&FLAG_SIZE_MSB){ data_size_msb v } + if(frame_flags&FLAG_MATCH_TIME){ + match_time_delta s + } if(frame_flags&FLAG_RESERVED) frame_res v for(i=0; i<frame_res; i++) @@ -606,6 +614,8 @@ flags[frame_code], frame_flags (v) otherwise data_size_msb is 0. 6 FLAG_CHECKSUM If set, the frame header contains a checksum. 7 FLAG_RESERVED If set, reserved_count is coded in the frame header. + 11 FLAG_MATCH_TIME If set, match_time_delta is coded in the frame + header, otherwise its 0. 12 FLAG_CODED If set, coded_flags are stored in the frame header. 13 FLAG_INVALID If set, frame_code is invalid. @@ -664,6 +674,13 @@ coded_pts (v) delta = last_pts - mask / 2 pts = ( (pts_lsb - delta) & mask ) + delta +match_time_delta + If FLAG_MATCH_TIME is not set, then this is 0 + This is the time difference in stream timebase units from the pts at which + the output from the decoder has converged independant of the availability + of previous frames (that is the frames are virtually identical no matter + if decoding started from the very first frame or from this keyframe). + lsb_pts Least significant bits of the pts in time_base precision. Example: IBBP display order @@ -738,7 +755,8 @@ back_ptr_div16 (v) back_ptr must point to a position up to 15 bytes before a syncpoint startcode, relative to position of current syncpoint. The syncpoint pointed to MUST be the closest syncpoint such that at least one keyframe - with a pts lower or equal to the current syncpoint's global_key_pts for + with a pts+match_time_delta lower or equal to the current syncpoint's + global_key_pts for all streams lies between it and the current syncpoint. A stream where EOR is set is to be ignored for back_ptr. @@ -769,7 +787,8 @@ has_keyframe the last syncpoint. keyframe_pts - The pts of the first keyframe for this stream in the region between the + The pts+match_time_delta of the first keyframe for this stream in the + region between the 2 syncpoints, in the stream's timebase. (EOR frames are also keyframes.) eor_pts