The unit and method relate generally to the quantization of digital data.
Systems and methods that quantize digital data, such as video data, are well known. For example, most video, still image and audio compression schemes use some form of quantization to reduce the bandwidth of the compressed data. Most of these known quantization systems are too slow for some applications and/or are too computationally expensive. Thus, it is desirable to provide a quantizer and method that overcomes the problems with the current techniques and it is to this end that the apparatus and method are directed.
The apparatus and method are particularly applicable to the quantization of video data streams and it is in this context that the apparatus and method will be described. It will be appreciated, however, that the apparatus and method has greater utility as it may be used to quantize other types of digital data and is not limited to video data which is the example of the application of the technology set forth below,
The apparatus 10 transcodes and stream video files over a mobile link whose bandwidth and quality changes often using adjustable video quantization to provide a variable bit rate streaming apparatus and method without the enormous storage requirements of the typical systems. As shown in
Once the video had been transcoded into a transcoded video, it is passed onto a quantizer 16 that performs quantization on the transcoded video to generate a quanitized video (having a particular bit rate and quantization appropriate for the link over which the video will be streamed) which can then be streamed over the mobile link to one or more mobile devices.
The quantizer may receive an input video 13 that has been compressed at a first quantization level Q1 (and thus have a first bit rate) and may output an output signal 15 that has been compressed at a second quantization level Q2 (and thus have a second bit rate). The quantizer may include a variable length decode (VLD) unit 22 that decodes the variable length decoding of the incoming compressed video bitstream to generate a stream of quantized DCT coefficients, an inverse quantizer unit 24 that removes the quantization and results in a stream of unquantized DCT coefficients. The current quantizer's technique is applicable for most block-based and transform based video compression standards. This quantizer architecture can be extended to many other transforms including wavelets. The quantizer may also include an inverse discrete cosine transform unit 26 that performs reverse DCT on the stream of coefficients and generates a stream of raw video data which means that the video data is in the pixel domain. The resultant stream of raw video data (which represents a frame of video pixel data) is then summed/compared by a summer unit 28 to a prior frame of pixel data (to perform motion compensation in the pixel domain) that is stored in a frame buffer 30 and the resultant video pixel data is fed into a second summer unit 32 which combines the resultant video pixel data with a motion compensated frame of pixel data (at the second quantization level) that is stored in a second frame buffer 44 (to again perform motion compensation in the pixel domain) to generate video pixel data that has been motion compensated for the previous frame at the old quantization level as well as the frame at the new quantization level. The resultant pixel data is then fed into a discrete cosine transform unit 34 that generate a new set of DCT coefficients based on the motion compensated video data frames. The new set of DCT coefficients are then quantized by a quantizer unit 36 at a second, different quantization level to generate quantized DCT coefficients that may be variable length coded using a variable length coder unit 38) and output as a compressed output signal at the second quantization level (and thus at the second bit rate.)
The quantizer 20 may implement, using a number of components, a first quantizer loop 52, a second quantizer loop 54 and a third quantizer loop 56 as shown by the dotted lines in
The second quantizer loop 54 may perform motion compensation between each frame of data on the encode side wherein the quantized coefficients output from quantizer 36 may be inverse quantized using an inverse quantizer unit 40 to generate coefficients, inverse discrete cosine transformed using an inverse discrete cosine transform unit 42 to generate frame pixel data at the new quantization level that is stored in the second frame buffer 44. The frame pixel data at the new quantization level is then compared to/summed with the pixel data from the inverse DCT unit 26.
The third quantizer loop 56 may enhance motion compensation of the decoder side by summing/comparing the video pixel data from the current frame to the video pixel data from the prior frame that is stored in the first frame buffer 30.
In the quantizer shown in
The above quantizer is also capable of adjusting region of interest on any given video frame, the essential idea behind this is that in a given video frame there will be two different quantization values will be used. The region that will have a lower quantization(higher quality) is determined by the motion vector information on the frame header . As a result elements that have higher movements in the picture will be lot clearer than the static elements. The region of interest is configurable, by default a 4×4 macro-block region is considered as the region of interest. The two different quantization levels are determined by configuration options provided to the quantizer (for example : region of interest quantization factor is 6 and the other region is kept at 8).
While the foregoing has been with reference to a particular embodiment of the invention, it will be appreciated by those skilled in the art that changes in this embodiment may be made without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims.
Number | Date | Country | |
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Parent | 12235129 | Sep 2008 | US |
Child | 13715846 | US |