CN101968962A - FAAC and FAAD2-based single track constant bit rate audio realtime coding and decoding error correcting method - Google Patents
FAAC and FAAD2-based single track constant bit rate audio realtime coding and decoding error correcting method Download PDFInfo
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- CN101968962A CN101968962A CN2010102877414A CN201010287741A CN101968962A CN 101968962 A CN101968962 A CN 101968962A CN 2010102877414 A CN2010102877414 A CN 2010102877414A CN 201010287741 A CN201010287741 A CN 201010287741A CN 101968962 A CN101968962 A CN 101968962A
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Abstract
The invention provides a free advanced audio coder(FAAC) and AAC audio decoder (FAAD2)-based single track constant bit rate audio realtime coding and decoding error correcting method, which mainly comprises that: a coder performs Hamming coding of fixed and variable frame headers, the Hamming coding of ID-SCE, SCETAG, a global scale factor and ID-END in a group, and Hamming coding of side information, packs a data area according to the size of a padding data area, performs Hamming coding of each data packet, separates check bit data from Hamming codes and stores the check bit data in the padding data area in turn; and a decoder acquires check bit data from the packing data area and performs the Hamming code error checking and correcting of corresponding data bits. On the premise of ensuring the structural integrity of an advanced audio coding (AAC) frame, the method has the capability of correcting errors of AAC data frames.
Description
Technical field
The present invention relates to a kind of audio frequency real time codec error correction method of the monophony fixed bit rate based on FAAC and FAAD2, its error correction method has error correcting capability to the AAC Frame, belongs to the communications field.
Background technology
Advanced audio (Advanced Audio Coding, be called for short AAC) be the sensing audio compression coding and decoding technology of new generation that on the MP3 basis, grows up, this technological synthesis the advantage of multiple main flow audio encoding and decoding technique, has signal compression than high, reconstruction tonequality is good, characteristics such as encoding-decoding process high modularization and sound channel flexible configuration.
In the real time codec system, the AAC Frame is in transmission course, error code cannot appear with avoiding, adopt cyclic redundancy check (CRC) code to carry out error detection, if generation error code, the AAC scrambler must retransmit the continuity that the error code Frame could guarantee the decoding output audio, but adopts the method can cause transmitting controlling mechanism complexity, system resource increase, poor robustness.In fact, under the prerequisite that guarantees the hardware platform reliability, data bit error rate in transmission link is very low, therefore can take in the AAC code stream, to add error checking and correction information, guarantee to carry out error correction behind the data error code, obtain correct Frame, make the decoding output audio not interrupt, and the transmission controlling mechanism unaffected, do not increase system resource, robustness height.
Summary of the invention
In order to guarantee the AAC correctness of data frame, the invention provides a kind of audio frequency real time codec error correction method of the monophony fixed bit rate based on FAAC and FAAD2.This error correction method mainly comprises: scrambler carries out the hamming coding respectively to fixing and variable frame head, ID_SCE, SCETAG, the global proportionality factor and ID_END are classified as one group carry out the hamming coding, side information hamming coding, divide into groups according to the size in padding data district in the data field, every group of data are carried out the hamming coding; From each Hamming code, isolate the check bit data, deposit the padding data district successively in; Demoder obtains the check bit data from the padding data district, and corresponding data bit is carried out Hamming code debugging and error correction.The present invention has error correcting capability to the AAC Frame under the prerequisite that guarantees AAC frame structure integrality.Concrete steps are as follows:
The step 1 scrambler carries out the hamming coding respectively to fixing and variable frame head;
The step 2 scrambler is classified as one group with ID_SCE, SCETAG, the global proportionality factor and ID_END and carries out the hamming coding;
The step 3 scrambler carries out the hamming coding to side information;
The step 4 scrambler divides into groups the data field according to the size in padding data district, every group of data are carried out the hamming coding;
The step 5 scrambler is isolated the check bit data from each Hamming code, deposit the padding data district successively in;
The step 6 demoder obtains the check bit data from the padding data district, and corresponding data bit is carried out Hamming code debugging and error correction.
Wherein, in the described step 1: the AAC scrambler is finished a frame pulse coded modulation (Pulse Code Modulation, abbreviation PCM) after the digital coding, more fixing and variable frame head are carried out the hamming coding respectively, the AAC data frame format is the audio data transport stream form in the present invention.
Wherein, in the described step 4: fixed bit rate of the present invention is 128kbps, the AAC scrambler is unfixing to the required bit number of dissimilar coding audio signals, the size in padding data district is unfixing yet, therefore need rationally divide into groups to the data field after encoding according to the size in padding data district, use the hamming coding afterwards, deposit the verification bit data in the padding data district, guarantee the integrality of AAC frame structure, on the AAC decorder platform that does not have corresponding Hamming code debugging and error correction, also can carry out normal decoder.
Wherein, in the described step 5: after the check bit data deposit the padding data district successively in and refer to that one group of data is finished hamming coding, isolate the check bit data and deposit the padding data district in, cover the padding data of corresponding bits number, then handle one group of data.
Wherein, in the described step 6: after the AAC demoder receives the AAC Frame, at first carry out normal decoder, make mistakes as decoding, then carry out Hamming code debugging and error correction from the padding data district taking-up check bit data of error data frame, then the Frame after the error correction is decoded again, the travelling speed that therefore requires the AAC demoder is 2 times of real-time decoding at least.
Principle of the present invention: add Hamming code error checking and correction information in the padding data district of AAC Frame, under the prerequisite that guarantees AAC frame structure integrality, the AAC Frame is had error correcting capability.
The present invention's advantage compared with prior art is:
1, do not destroy the frame structure of AAC;
2, the transmission controlling mechanism unaffected, do not increase system resource, robustness height.
Description of drawings
Fig. 1 is the error correction method overall schematic that the present invention proposes;
Fig. 2 is a coding process flow diagram of the present invention;
Fig. 3 is a padding data frame structure 1 of the present invention;
Fig. 4 is a padding data frame structure 2 of the present invention;
Fig. 5 is a padding data frame structure 3 of the present invention;
Fig. 6 is decoding process figure of the present invention.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is described further.
The invention provides a kind of audio frequency real time codec error correction method of the monophony fixed bit rate based on FAAC and FAAD2.Referring to accompanying drawing 1, this error correction method mainly comprises: scrambler carries out hamming coding (110) respectively to fixing (101) and variable (102) frame head, ID_SCE (103), SCETAG (104), the global proportionality factor (105) and ID_END (109) are classified as one group carry out the hamming coding, side information (106) hamming coding, divide into groups according to the size of padding data district (108) in data field (107), every group of data are carried out the hamming coding; From each Hamming code, isolate the check bit data, deposit padding data district (108) successively in; Demoder obtains the check bit data from the padding data district, and corresponding data bit is carried out Hamming code debugging and error correction (111).The present invention has error correcting capability to the AAC Frame under the prerequisite that guarantees AAC frame structure integrality.
The treatment scheme of coded program is referring to accompanying drawing 2, and the AAC scrambler is at first finished normal coding (201); Judge that then whether padding data is more than or equal to 15 (202); If less than 15, then can't carry out hamming coding (203) to these frame data; Otherwise, continue to judge that whether padding data is more than or equal to 25 (204); If less than 25, then adopt padding data frame structure 1 to carry out hamming coding (205) to these frame data; Otherwise, continue to judge that whether padding data is more than or equal to 39 (206); If less than 39, then adopt padding data frame structure 2 to carry out hamming coding (207) to these frame data; Otherwise, adopt padding data frame structure 3 to carry out hamming coding (208) to these frame data.
Padding data adopts padding data frame structure 1 to carry out the hamming coding more than or equal to 15 and less than 25 o'clock, referring to accompanying drawing 3,3bit check mark (301)=100 is set at first; Then, to 28bit fixedly frame head use the 6bit check bit to carry out the hamming coding, afterwards the 6bit check bit is deposited in check information 1 (302); Then, use the 6bit check bit to carry out the hamming coding, at last the 6bit check bit is deposited in check information 2 (303) the variable frame head of 28bit.
Padding data adopts padding data frame structure 2 to carry out the hamming coding more than or equal to 25 and less than 39 o'clock, referring to accompanying drawing 4,3bit check mark (401)=110 is set at first; Then, to 28bit fixedly frame head use the 6bit check bit to carry out the hamming coding, afterwards the 6bit check bit is deposited in check information 1 (402); Secondly, use the 6bit check bit to carry out the hamming coding to the variable frame head of 28bit; Afterwards the 6bit check bit is deposited in check information 2 (403); Then, ID_SCE, SCETAG, the global proportionality factor and ID_END are classified as one group, use the 5bit check bit to carry out the hamming coding; Afterwards the 5bit check bit is deposited in check information 3 (404); At last, use the 5bit check bit to carry out the hamming coding, after finishing the 5bit check bit deposited in check information 4 (405) side information.
Padding data adopted padding data frame structure 3 to carry out the hamming coding more than or equal to 39 o'clock, referring to accompanying drawing 4,3bit check mark (501)=111 was set at first; 6bit verification group number is set, and the computing method of verification group number are hereinafter introduced; The 2bit grouping information is set, and the computing method of grouping information are hereinafter introduced; Then, to 28bit fixedly frame head use the 6bit check bit to carry out the hamming coding, afterwards the 6bit check bit is deposited in check information 1 (504); Secondly, use the 6bit check bit to carry out the hamming coding to the variable frame head of 28bit; Afterwards the 6bit check bit is deposited in check information 2 (505); Then, ID_SCE, SCETAG, the global proportionality factor and ID_END are classified as one group, use the 5bit check bit to carry out the hamming coding; Afterwards the 5bit check bit is deposited in check information 3 (506); Next step uses the 5bit check bit to carry out the hamming coding to side information, afterwards the 5bit check bit is deposited in check information 4 (507); At last, the hamming coding is carried out in data field grouping, after finishing check bit is deposited in residual buffer district (508).
The computing method of grouping information and verification group number are as follows: the bit number=padding data number-3bit check information-6bit verification group number-2bit grouping information-6bit check information 1-6bit check information 2-5bit check information 3-5bit check information 4 that a) can be used for data field hamming coding; B) 2bit grouping information, the grouping of expression data field is totally 4 classes, and 00 representative is 57bit for every group, needs 6 bit check bit, 01 representative is 120bit for every group, need 7 bit check bit, 10 representatives are 247bit for every group, need 8 bit check bit, 11 representatives are 502bit for every group, need 9 bit check bit, and last group data bit is counted deficiency, then zero padding after grouping; C) according to the bit number that can be used for data field hamming coding divided into groups in the data field, group forming criterion is at first to divide into groups at most; Secondly maximum to the data verification.For example, bit number=16 that can be used for data field hamming coding, 00,01 and 10 type packet then, packet count all is 2, but 10 type packet can be carried out verification to 2*247bit, so 2bit grouping information=10, the data field has 2 groups of data need carry out the hamming coding, and current data frame has 6 groups of data need carry out the hamming coding, so 6bit verification group number=000110.
After the AAC scrambler is finished coding, data are sent to transmission link, obtain the AAC Frame in the AAC demoder in the transmission link and decode, treatment scheme is referring to accompanying drawing 6.After the AAC demoder obtains the AAC Frame, at first decode (601); Then judge whether to be correctly decoded (602); If be correctly decoded then finish, otherwise utilize the check information in the padding data district to carry out debugging and error correction (603); Decode once more (604).
The english abbreviation that occurs in the Figure of description, its implication is as follows:
CRC: CRC;
ID_SCE: monophonic identification identifier;
SCETAG: monophonic label;
ID_END: end identifier.
Claims (5)
1. audio frequency real time codec error correction method based on the monophony fixed bit rate of FAAC and FAAD2, it is characterized in that: this method specifically may further comprise the steps:
(1) scrambler carries out the hamming coding respectively to fixing and variable frame head;
(2) scrambler is classified as one group with ID_SCE, SCETAG, the global proportionality factor and ID_END and carries out hamming coding;
(3) scrambler carries out the hamming coding to side information;
(4) scrambler divides into groups the data field according to the size in padding data district, and every group of data are carried out the hamming coding;
(5) scrambler is isolated the check bit data from each Hamming code, deposits the padding data district successively in;
(6) demoder obtains the check bit data from the padding data district, and corresponding data bit is carried out Hamming code debugging and error correction.
2. the audio frequency real time codec error correction method of a kind of monophony fixed bit rate based on FAAC and FAAD2 according to claim 1, it is characterized in that: in the described step (1): the AAC scrambler is finished after the frame PCM digital coding, again fixing and variable frame head are carried out the hamming coding respectively, the AAC data frame format is the audio data transport stream form in the present invention.
3. the audio frequency real time codec error correction method of a kind of monophony fixed bit rate based on FAAC and FAAD2 according to claim 1, it is characterized in that: in the described step (4): fixed bit rate of the present invention is 128kbps, the AAC scrambler is unfixing to the required bit number of dissimilar coding audio signals, the size in padding data district is unfixing yet, therefore need rationally divide into groups to the data field after encoding according to the size in padding data district, use the hamming coding afterwards, deposit the verification bit data in the padding data district, guarantee the integrality of AAC frame structure, on the AAC decorder platform that does not have corresponding Hamming code debugging and error correction, also can carry out normal decoder.
4. the audio frequency real time codec error correction method of a kind of monophony fixed bit rate based on FAAC and FAAD2 according to claim 1, it is characterized in that: in the described step (5): after the check bit data deposit the padding data district successively in and refer to that one group of data is finished hamming coding, isolate the check bit data and deposit the padding data district in, cover the padding data of corresponding bits number, then handle one group of data.
5. the audio frequency real time codec error correction method of a kind of monophony fixed bit rate based on FAAC and FAAD2 according to claim 1, it is characterized in that: in the described step (6): after the AAC demoder receives the AAC Frame, at first carry out normal decoder, make mistakes as decoding, then carry out Hamming code debugging and error correction from the padding data district taking-up check bit data of error data frame, then the Frame after the error correction is decoded again, the travelling speed that therefore requires the AAC demoder is 2 times of real-time decoding at least.
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Cited By (1)
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