Bit rate estimation in data or video compression
To reduce the complexity of rate-distortion cost computation in AVC (MPEG4 Part2/H.264), a bit rate estimation method is used to avoid entropy coding during Intra and Inter mode decision. The bit rate estimation method predicts the number of entropy coded bits based on the quantized transform coefficients, thus avoiding the need to entropy code the quantized transform coefficients at each decision iteration.
1. A method of transmitting compressed data at a minimized bit rate over a network, the method comprising:
estimating a minimized bit rate required for compressing the data using an encoding scheme comprising
predicting bit rates of each of a plurality of symbols of the encoding scheme, without compressing the data to be compressed, based on characteristics of the data and codes of the encoding scheme, and
computing a computed bit rate required for compressing the data by summing the bit rates predicted for each of the symbols;
compressing the data using the computed bit rate to produce compressed data; and
transmitting the compressed data to a network.
2. The method of claim 1 , wherein the encoding scheme is variable length coding.
3. The method of claim 2 , wherein the encoding scheme is context adaptive variable length coding.
4. The method of claim 3 , wherein the plurality of symbols of the encoding scheme include coefficient tokens, trailing ones, level of nonzero coefficients, total number of zeros before the last coefficient, and runs of non-zero coefficients.
5. The method of claim 1 including processing the data with at least one of a transform and quantization before predicting the bit rates of each of the plurality of symbols.
6. The method of claim 1 , including predicting the bit rates of each of the plurality of symbols iteratively to determine optimized parameters for compressing the data.
7. The method of claim 1 , including predicting the bit rates of each of the plurality of symbols iteratively to determine optimized mode for compressing video frames as the data.
8. A method of transmitting compressed video data over a network, the method comprising:
determining an optimum mode for compressing video data comprising
finding difference image data of a selected block of a video frame using a predictive mode,
transforming and quantizing the difference image data to produce quantized data,
estimating a minimized bit rate required for compressing the quantized data using an encoding scheme, wherein estimating the minimized bit rate includes
predicting bit rates of each of a plurality of symbols of the encoding scheme, without compressing the quantized data to be compressed, based on characteristics of the quantized data and codes of the encoding scheme, and
computing a computed bit rate by summing the bit rates predicted for each of the symbols;
iteratively repeating the foregoing steps, using different predictive modes, until an optimum mode for compressing the video data is found;
compressing the video data using the optimized mode to produce compressed video data; and
transmitting the compressed video data to a network.
9. The method of claim 8 , wherein the predictive modes are based on intra and inter mode video data compression.
10. The method of claim 8 , wherein the encoding scheme is variable length coding.
11. The method of claim 10 , wherein the encoding scheme is context adaptive variable length coding.
12. The method of claim 11 , including estimating the bit rate based, in part, on at least one symbol code of context adaptive variable length coding.
13. The method of claim 8 , including compressing the video data according to one of MPEG4 Part2 and ITU-T H.264.
14. The method of claim 11 , wherein the plurality of symbols of the encoding scheme include coefficient tokens, trailing ones, level of nonzero coefficients, total number of zeros before the last coefficient, and runs of non-zero coefficients.