【 Weak current College 】 audio codec technology and its implementation

First, the audio and video encoding and compression of the International Organization for Standardization standard introduction
Internationally, there are two responsible for video and audio encoding standards organization, VCEG (VideocodeExpertGroup), the International Telecommunication Union of video coding experts group, one is a MPEG (MotionPictureExpertGroup), is the International Organization for Standardization (ISO) image of movement. Both video and audio encoding standards organization is the Visual audio codec made very important contributions: one is the advance audio coding technology, a is the audio codec.
Audio codec involves a number of video and audio processing technology, every technology improvements are to contribute to the Visual audio encoding, but as a complete, efficient encoding scheme, you need to concentrate all of humanity in video and audio codec's latest wisdom. Personal or company research results, all hope was standardization organization, its economic return is the standard usage.
The two standards organizations to develop relevant coding standards have access to a wide range of applications, standards have VCEG H.261 (International Telecommunication Union selected for videoconferencing video compression standards), H.262 (this standard is identical with the MPEG-2 is VCEG joint with MPEG encoding group developed standard compressed JVT, VCEG H.262, publication is published MPEG-2 MPEG), H.263 (the International Telecommunication Union standard was selected as the video phone's video compression standard, and enhanced version of H.263 +, H.263 + +), H.264 (this standard is in May 2002 VCEG as next-generation interactive video communication standards). MPEG is much more famous, standards have MPEG-1, MPEG-2, MPEG-4, MPEG-7 and MPEG-21, MPEG-1 compression standard adopted for VCD, MPEG-2 compression standard for DVD, interactive multimedia MPEG-4 is to develop communication compression standard, is the Internet MPEG-7 video retrieval developing compression standard.
Compression standard developed by VCEG H.26X is for a single rectangle video objects, and their pursuit of higher compression efficiency. The reason why the current MPEG-4 is very hot, because MPEG-4 is based on more than one audio object's coding standard, which is ideal for multimedia applications on the Internet. On the Internet multimedia information, much of it can be divided into multiple video objects, such as computer-generated animation programmes, TV news programs, and in the live video image coding, in an image rectangle box hard real-time identification of multiple video objects, or to a video source as a rectangle object to encode the video.
Published in 1997, VCEG H.263 compression standard, developed a short-term development plans and long-term development plan H.26N H.26L, H.26N developed into H.263 + and + the +, H.263 H.26L after five years of development, in May 2002 as H.264 compression standard for publishing.
H.263 MPEG in VCEG publishing, publishing the MPEG-4SP (i.e. MPEG-4 first Board), in the version introduces two important concepts: one is a video source to multiple video and audio encoding, an object is a stream transmission exception handling (especially wireless transmission application). From here you can see, VCEG committed to efficient video coding, MPEG and more focused on systems and frameworks.
In the fourth quarter of 2001, VCEGH.26L development to TML9.0, MPEG and VCEG again a joint group of experts on joint video encoding, the JVT H.26L algorithm improvement and perfection, in May 2003, VCEG publishes h.264 compression standard. MPEG in the JVT on H.26L compression algorithm changes based on the technical specifications into MPEG-4 standards, as published, namely MPEG-4PART10 MPEG-4, third edition, MPEG-4AVC. H.264 and MPEG-4AVC represent the humankind in video and audio codec's latest results.
For a single rectangle video object, MPEG-4AVC than MPEG-4 Second Edition MPEG-4ACE compression efficiency 30% or more.

Second, H.264 and MPEG-4PART10 technical notes
With previous H.263 Video compression standard c++ and MPEG-4ACE compared to H.264 and MPEG-4PART10 adopts new algorithms, mainly in the following areas:
1, motion search
A multi-reference frame, the introduction of
The introduction of up to five reference frames.
B, multiple BLOCK shape
16 * 16 * 16, 8, 16, 8 * 8 * 8, 8 * 4, 8, 4 * 4 * 4 seven BLOCK shape.
C, sport a higher search accuracy
1/2 pixel precision search employs 6 order filter, search accuracy has greatly improved. Also introduced 1/4 pixel precision search and 1/8 pixel precision searching.
2. residual coding
A, adopt an integral 4 * 4DCT transform
B, quantization technology improvement
C adopt DE-BLOCK technology
D, SP frame technology
These technical changes, on the one hand, improving compression efficiency, on the other hand, a substantial increase in operational strength, greatly improved the implementation difficult.