With the development of computer networks and multimedia technology, digital video applications are more and more wide, such as DVD, online conferencing services, digital TV, etc. In these video processing and communication, efficient video coding is a key technique.
H.264 / AVC is the latest generation of video coding standards proposed by ITU-T video coding expert group and ISO / IEC moving image expert group. H.264 has many excellent performance [1]: Compression ratio, compared with existing coding standards (H.263, MPEG-4 Simple Profile), can save approximately 50% of the code stream under the same video quality Better image quality, wider adaptability, better meet real-time (video conferencing) and non-real-time (storage, broadcasting, etc.). Real-time coding of H.264 has a large engineering significance and economic value on the DSP.
1 H.264 standard introduction and DSP platform
1.1 H.264 standard introduction
H.264 is the latest video coding standard established by ITU-T and ISO / IEC, which is proposed by ITU-T in 1997 and forms a final standard draft in March 2003. It contains many of the latest research results in the field of video compression, mainly using the following technology [1]:
(1) Divide the coded into the coding layer VCL (Video Coding Layer) and the transport layer NAL (Network Abstract Layer). The coding layer and the transport layer are separated, which is advantageous for the expansion of H.264.
(2) H.264 The intra prediction in the airspace is used, two predictive modes: Intra1616 and Intra44. The intra1616 has four prediction methods, and Intra4 × 4 has nine prediction methods.
(3) For inter-frame prediction, the prediction mode is added, and a total of seven prediction modes are added. The prediction block can be minimized from 16 × 16 to 4 × 4.
(4) Increase the number of reference frames, making predictions more accurate.
(5) Place the deck effect filtering in the coding ring and improve the subjective quality of the image.
(6) The B frame can be used as a reference frame while separating the decoding order of the image is separated from the display order.
(7) Adopt a whole-co-correction change and improve the transformation speed.
(8) Adopt new entropy encoding methods such as CAVLC, CABAC to improve the encoding effect.
(9) Improve the anti-comment capability of the code stream, such as dividing the encoded data, one frame image can be flexibly divided into several slice, etc.
1.2 DSP platform based on Blackfin533
Blackfin533 is a high-performance video processing chip in the ADI's Blackfin Series. Its frequency is up to 600MHz, which can handle 1200M times multiplication operation per second. It has a large number of dedicated instructions for the video, and multiple instructions can be handled in parallel.
Overall, Blackfin533 is divided into two parts: the kernel and system interface. Core refers to the processor, L1 memory, event controller, internal-core timer, etc .; system interface refers to the SPORT interface, PPI interface, SPI interface, external storage controller, DMA controller, and external resources with them.
The BLACK533 development platform schematic is shown in Figure 1. The analog video signal output by the camera is converted to a digital signal from the 7113 video chip, which enters the Blackfin 533's PPI interface into the Blackfin533, and the compressed code stream is transmitted to the PC. This system is started by flash, the original image, reference frame, and other variables during the encoding process are stored in the SDRAM.
Figure 2 is a video input module of the H.264 encoding system. The 7113 chip reads the analog signal output from the video terminal, and outputs the digital signal to the Blackfin533 via the parallel port. The BlackFin 533 is configured by the I2C bus to output YUV mode, ITU656 mode, and enhances ITU656 mode.
Figure 1 Blackfin533 platform overall frame map
Figure 2 Video input module
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Figure 3 H.264 encoding module diagram, technology area
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