CN100563336C - A kind of constant code rate control method based on mobile TV - Google Patents

The invention provides a kind of control method of the constant code rate based on mobile TV, described method is divided into several image sets to present image, adopts frame level bit-rate control and macro-block level Rate Control to come image is encoded to each image sets.Constant code rate control method provided by the invention, the control precision height, the code stream fluctuation of output is little, and the coding subjective picture quality is good, and computation complexity is very low, is fit to the application of various software and hardware codings.

A kind of constant code rate control method based on mobile TV

Technical field

The present invention relates to the video coding technique of mobile TV, particularly relate to a kind of constant code rate control method based on mobile TV.

Background technology

In the real time communication of video, code stream need transmit on the network of different bandwidth.For when guaranteeing higher relatively video image quality, improve utilization rate of network resource as much as possible, just the control to the transmission code rate of video flowing has proposed demand.Present Rate Control technology is exactly to control the occupancy of bit in the buffering area by ceaselessly adjusting coding parameter, makes it reach stable as far as possible, the situation of overflow and underflow do not occur; Guaranteeing to guarantee the stable of picture quality under the stable prerequisite of buffering bit occupancy simultaneously as far as possible.In various video compression standards, Rate Control is being played the part of very important role always, for example: the TM5 of MPEG2, TMN8 H.263 etc.Yet existing rate control algorithm all is at the SD image, is not suitable for the application of mobile TV, because the application characteristic of mobile TV is that code check is low, is approximately 10～20Kbps; Frame per second is low, is approximately 10fps～15fps; The structure of image sets GOP is IPPP...... simultaneously, therefore is necessary to design a kind of bit rate control method that mobile TV is used that satisfies.

Summary of the invention

The object of the present invention is to provide a kind of control method of the constant code rate based on mobile TV, described bit rate control method is that unit carries out constant code rate control with image sets (GOP).Described method is the control precision height not only, and the code stream fluctuation of output is little, and the coding subjective picture quality is good, and computation complexity is low simultaneously, is fit to the application of various software and hardware codings.

The object of the present invention is achieved like this: a kind of control method of the constant code rate based on mobile TV, described method realizes Rate Control based on the quantization parameter value of the video image code stream of regulating mobile TV, described code stream comprises I frame and P frame, and concrete steps are as follows:

Step 2, the control of achieve frame level bit-rate, it further comprises:

The bit number Bit that step 2.1, the current P frame of calculating can access _{Cur_pic}=λ _Cur* (Bit _Gop-Bit _{Cur_gop_used}), Bit in the following formula _{Cur_gop_used}Be the already used bit number of current GOP, λ _CurBe the weight coefficient of current P two field picture, calculate according to the complexity of present image P frame;

The quantization parameter QP of i P frame in step 2.2, the every frame of calculating _{P_i}, i=1,2,3......;

QP P _ i = α × QP ref + η × L 0 - 2 n L 0 - 2 , n = 1,2 , . . . , L 0 - 1

Step 2.3, according to the quantization parameter of each frame, again each frame is encoded, until frame end; If frame does not finish, then jump to step 1;

Step 3, realization macro-block level Rate Control, it further comprises:

The average absolute distortion MAD of step 3.1, computing macro block is designated as MAD _{MB_cur},

MAD MB _ cur ( x , y ) = 1 N 2 Σ i = 0 N - 1 Σ j = 0 N - 1 | F n ( i , j ) - F n - 1 ( i + x , j + y ) | , - w ≤ x , y ≤ w

In the following formula, F _nAnd F _N-1Be respectively macro block corresponding in current macro and the former frame, size is N * N, and N is a number of pixels that macro block comprises;

The target bits Bit of step 3.2, calculating current macro _{MB_cur}:

Bit MB _ cur = θ × MAD MB _ cur AVG ( MAD ) × Bit cur _ pic M

In the following formula, θ is an experiment value, is determined general desirable 0.93 by macro block (mb) type and frame type; M is the macroblock number that present frame comprises; Bit _{Cur_pic}Bit for the present frame distribution; AVG (MAD) is the arithmetic average of the MAD of current encoded macro block;

The quantization parameter of step 3.4, calculating current macro is designated as QP _{MB_cur},

QP _{MB_cur}＝λ×QP _{MB_prev}+ΔQP

Step 3.5, adjust quantization parameter, finish the coding of current macro according to the Δ QP of macro-block level;

Step 3.6, judge whether all macroblock codings of present image are finished,, then jump to step 2 if macroblock coding is finished; If macroblock coding is not finished, then jump to step 3.1;

Step 4, upgrade the coded quantization parameter of present image, finish the present frame coding according to step 2; Judge whether the frame coding of two field pictures all among the present image group GOP is finished, if finish, then continues step 5, otherwise, Bit upgraded _Less, jump to step 2.1;

If the coding of all images group of step 5 present image is all finished, then finish, otherwise jump to step 1.

The present invention has been owing to adopted above-mentioned technical scheme, compared with prior art, control precision height not only, the code stream fluctuation of output is little, and the coding subjective picture quality is good, and computation complexity is low, is fit to the application of various software and hardwares.

Embodiment

Below will the control method of the constant code rate based on mobile TV of the present invention be described in further detail.

Present embodiment requires comprising 1 I frame, and the image of 14 P frames is encoded and transmission code rate control, and the image size is 176x144, and target frame rate is 30Kbps.The control method of a kind of constant code rate based on mobile TV provided by the invention, described method realizes that based on regulating quantization parameter QP value the specific implementation step is as follows:

The bit number that current P frame can access is calculated in step 2, the control of achieve frame level bit-rate;

The bit number Bit that step 2.1, the current P frame of calculating can access _{Cur_pic}=λ _Cur* (Bit _Gop-Bit _{Cur_gop_used}), Bit in the following formula _{Cur_gop_used}Be the already used bit number of current GOP, λ _CurBe the weight coefficient of present image, calculate according to the complexity of present image P frame; If the code check that current GOP obtains is Bit _Gop=27.882kbps, the bit number Bit that the I frame uses _I=11584bit, the bit number Bit that the P frame uses _P=920bit, Bit like this _{Cur_gop_used}=12504bit, Bit _Gop-Bit _{Cur_gop_used}=15378bit calculates λ to the P frame _CurGet 0.10, then the Bit of P frame _{Cur_pic}=1536bit.

The quantization parameter QP of i P frame in step 2.2, the every frame of calculating _{P_i}, i=1,2,3......;

QP P _ i = α × QP ref + η × L 0 - 2 n L 0 - 2 , n = 1,2 , . . . , L 0 - 1

Step 2.3, according to the quantization parameter of each frame, again each frame is encoded, until frame end; If frame does not finish, then jump to step 1;

Step 3, realization macro-block level Rate Control;

The average absolute distortion of step 3.1, computing macro block (MAD, Mean Absolute Distortion) is designated as MAD _{MB_cur},

MAD MB _ cur ( x , y ) = 1 N 2 Σ i = 0 N - 1 Σ j = 0 N - 1 | F n ( i , j ) - F n - 1 ( i + x , j + y ) | , - w ≤ x , y ≤ w

In the following formula, F _nAnd F _N-1Be respectively macro block corresponding in current macro and the former frame, size is N * N.

Step 3.2, the average absolute distortion of calculating current coded macroblocks are designated as AVG (MAD), are the current macro arithmetic means of the MAD of coded macroblocks.

The target bits of step 3.3, calculating current macro is designated as Bit _{MB_cur},

Bit MB _ cur = θ × MAD MB _ cur AVG ( MAD ) × Bit cur _ pic M

In the following formula, θ is an experiment value, determines that by macro block (mb) type and frame type present embodiment gets 0.93;

For the P frame, the bit Bit that present frame distributes _{Cur_pic}=1536bit, N=176x144/16=1584 is to a macro block of P frame, MAD _{MB_cur}=3.1, the front is the arithmetic average AVG of the MAD of coded macroblocks (MAD)=2.7, then Bit _{MB_cur}=2.8;

The quantization parameter of step 3.4, calculating current macro is designated as QP _{MB_cur},

QP _{MB_cur}＝λ×QP _{MB_puev}+ΔQP

For P frame: QP _{MB_prev}=46, ω=3.1/2.7=1.1, Δ QP=0, i _{MB_left}There is not i _{MB_upleft}, i _{MB_up}And i _{MB_upright}Exist, then i _{MB_left}=0, i _{MB_upleft}=1, i _{MB_up}=1, i _{MB_upright}=1, Bit _{MB_left}=0, Bit _{MB_upleft}=3.2, Bit _{MB_up}=2.5, Bit _{MB_upright}=2.8, MID (Bit _MB)=2.5, then

Step 3.5, adjust quantization parameter, finish the coding of current macro according to the Δ QP of macro-block level;

Step 3.6, judge whether all macroblock codings of present image are finished,, then jump to step 2 if macroblock coding is finished; If macroblock coding is not finished, then jump to step 3.1;

Step 4, upgrade the coded quantization parameter of present image, finish the present frame coding according to step 2; Judge whether the frame coding of two field pictures all among the present image group GOP is finished, if finish, then continues step 5, otherwise, Bit upgraded _Less, jump to step 2.1;

If the coding of all images group of step 5 present image is all finished, then finish, otherwise jump to step 1.

The embodiment coding result shows that the constant code rate control method based on mobile TV of the present invention not only has the control precision height, the little advantage of code stream fluctuation of output, and also the coding subjective picture quality is good, and computation complexity is low simultaneously.

1, a kind of control method of the constant code rate based on mobile TV, described method realizes Rate Control based on the quantization parameter value of regulating the video image code stream, described code stream comprises I frame and P frame, it is characterized in that, described bit rate control method is realized by following steps:

Step 2, the control of achieve frame level bit-rate, it further comprises:

The bit number Bit that step 2.1, the current P frame of calculating can access _{Cur_pic}=λ _Cur* (Bit _Gop-Bit _{Cur_gop_used}), Bit in the following formula _{Cur_gop_used}Be the already used bit number of current GOP, λ _CurBe the weight coefficient of current P two field picture, calculate according to the complexity of present image P frame;

The quantization parameter QP of i P frame in step 2.2, the every frame of calculating _{P_i}, i=1,2,3......;

QP P _ i = α × QP ref + η × L 0 - 2 n L 0 - 2 , n = 1,2 , . . . , L 0 - 1

Step 2.3, according to the quantization parameter of each frame, again each frame is encoded, until frame end; If frame does not finish, then jump to step 1;

Step 3, realization macro-block level Rate Control, it further comprises:

The average absolute distortion MAD of step 3.1, computing macro block is designated as MAD _{MB_cur},

MAD MB _ cur ( x , y ) = 1 N 2 Σ i = 0 N - 1 Σ j = 0 N - 1 | F n ( i , j ) - F n - 1 ( i + x , j + y ) | , - w ≤ x , y ≤ w

In the following formula, F _nAnd F _N-1Be respectively macro block corresponding in current macro and the former frame, size is N * N, and N is a number of pixels that macro block comprises;

The target bits Bit of step 3.2, calculating current macro _{MB_cur}:

Bit MB _ cur = θ × MAD MB _ cur AVG ( MAD ) × Bit cur _ pic M

In the following formula, θ is an experiment value, is determined general desirable 0.93 by macro block (mb) type and frame type; M is the macroblock number that present frame comprises; Bit _{Cur_pic}Bit for the present frame distribution; AVG (MAD) is the arithmetic average of the MAD of current encoded macro block;

The quantization parameter of step 3.4, calculating current macro is designated as QP _{MB_cur},

QP _{MB_cur}＝λ×QP _{MB_prev}+ΔQP

Step 3.5, adjust quantization parameter, finish the coding of current macro according to the Δ QP of macro-block level;

Step 3.6, judge whether all macroblock codings of present image are finished,, then jump to step 2 if macroblock coding is finished; If macroblock coding is not finished, then jump to step 3.1;

Step 4, upgrade the coded quantization parameter of present image, finish the present frame coding according to step 2; Judge whether the frame coding of two field pictures all among the present image group GOP is finished, if finish, then continues step 5, otherwise, Bit upgraded _Less, jump to step 2.1;

If the coding of all images group of step 5 present image is all finished, then finish, otherwise jump to step 1.