Simultaneous search for different resync-marker patterns to recover from corrupted MPEG-4 bitstreams

A method for recovering from an error in an f_code in a video object plane (VOP) header at a start of a frame in a video sequence comprising:

• detecting a unique start code at a start of a VOP;
• decoding a VOP header that follows the VOP, the VOP header containing the f_code for the VOP;
• when the f_code contains an error:
• (a) searching in a bitstream following the VOP header for a next resync marker by searching for a variable-length resync marker followed by a video packet VP header, wherein a bit length of the variable-length resync marker depends on a value of the f_code that contains the error;
• (b) when the next resync marker is detected, extracting a macroblock number from the VP header, the macroblock number being an identifier within the frame for a first macroblock in the video packet;
• (c) processing macroblock data in a data field of the video packet to generate pixel data or pixel-error terms for display, beginning with the first macroblock identified by the macroblock number;
• continuing to search the bitstream for other next resync markers and processing macroblocks for other video packets by repeating steps (a), (b), and (c) until a next unique start code is detected for a next VOP;
• when the f_code does not contain the error:
• (f) searching in the bitstream following the VOP header for a next resync marker by searching for a fixed-length resync marker that is followed by a video packet VP header, wherein a bit length of the fixed-length resync marker is indicated by the value of the f_code from the VOP header;
• (g) when the next resync marker is detected, extracting a macroblock number from the VP header, the macroblock number being an identifier within the frame for a first macroblock in the video packet;
• (h) processing macroblock data in a data field of the video packet to generate pixel data or pixel-error terms for display, beginning with the first macroblock identified by the macroblock number;
• and
• continuing to search the bitstream for other next resync markers and processing macroblocks for other video packets by repeating steps (f), (g), and (h) until a next unique start code is detected for a next VOP,
• whereby macroblock data is processed for video packets in the VOP having the error in the f_code.

A motion-picture-experts group (MPEG) bitstream decoder comprising:

• parser means for receiving a bitstream containing bit errors, the bitstream encoding compressed video arranged as video object planes (VOP) each having a plurality of video packets (VP);
• macroblock decoder means, coupled to the parser means, for extracting video macroblocks from data fields in the bitstream;
• start-code decoder means, coupled to the parser means, for detecting a start code in the bitstream, the start code for marking a start of a video object plane;
• VOP header means, coupled to the parser means, for reading a length code from a VOP header that follows the start code;
• multi-pattern resync marker decoder means, coupled to the parser means and receiving the length code from the VOP header means, for detecting a resync marker in the bitstream having a bit-length indicated by the length code and for signaling the macroblock decoder means to extract the video macroblocks when the resync marker is detected, the resync marker for marking a beginning of a video packet;
• and
• code-error recovery means, activated when the VOP header means is unable to read the length code when the VOP header contains a bit error, for signaling the multi-pattern resync marker decoder means to search the bitstream for a plurality of resync marker patterns having different bit lengths, the multi-pattern resync marker decoder means signaling the macroblock decoder means to extract the video macroblocks when the bitstream contains any of the plurality of resync marker patterns;
• wherein the resync marker in a corrupted bitstream is detected when a bit error occurs in the length code in the VOP header,
• whereby the bitstream is recovered from the length code that is corrupted.