Inverse Transform : The transform coefficients are multiplied by an integer number to restore its original value. This information is used to recreate a sequence of video images. It decodes the syntax elements and extracts the information such as quantized transform coefficients, prediction information and others. Decoderīitstream Decoding : The compressed H.264 bitstream is received at a decoder. Finally, the encoded bitstream can then be stored or transmitted. These encoding methods produce an efficient, compact binary representation of the video. The values such as quantized transform coefficients, information about the structure of the compressed data and the compression tools used during encoding are converted into binary codes using variable length, arithmetic, or entropy coding. The proper selection of the quantization parameter decides the trade-off between the efficiency and the decoded image quality.īitstream encoding : The prediction and transform operations produce several values that need to be encoded. The transform coefficients are quantized, and the result is a block in which most of the coefficients are zero, with a few non-zero coefficients. The transform outputs a set of coefficients, and these coefficients are used as a weighting factor to a standard basis pattern at the decoder. This transform is a particular type of discrete cosine transform (DCT). Transform : The residual block of prediction is transformed using a 4×4 integer transform. The difference between the original input samples and the predicted samples (either intra or inter-block) is called the residual of prediction. For all remaining pictures, inter prediction coding is used, that employs motion compensation (temporal coding) with the help of motion estimation. The first frame of a video is always encoded using intra prediction. Inter prediction operation uses different blocks ranging from 16×16 to 4×4 size to predict pixels in the current frame using similar regions in previously coded and transmitted frames. The intra prediction uses a block size of 4×4 and 16×16 to predict the current macroblock from the surrounding previously coded pixels within the same frame. The prediction of the current frame-block is carried out either by intra prediction or inter prediction. Prediction : The typical encoding operation begins with the splitting of each frame of video into units of a macroblock of 16×16 or 4×4 pixels. A simple overview of AVC encoder and decoder processes is highlighted in the form of block diagram below. Whereas, decoder carries out the complementary process of decoding, inverse transform, and reconstruction to obtain a video output. The encoder follows the prediction, transform, and encoding process to produce a compressed H.264 bitstream. Advanced Video Coding WorkingĪny advanced video coding technique consists of an encoder to convert a video into a compressed format and a decoder to convert a compressed video back to its original video. However, the use of Advanced Video Coding technology for streaming online video is free to end-users. This technology is protected by patents owned by various parties and the majority of the patents are administered by MPEG LA. AVC builds on the concepts of previous standards and offers good video quality at substantially lower bit rates. However, the standard does not specify algorithms to encode video, that is left open to the manufacturers. The AVC standard defines a syntax for encoding video and a method for decoding back the video sequence. It was jointly standardised by the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG) to help manufacturers to inter- operate.ĪVC is also referred to as H.264 or MPEG-4 AVC and first published in 2003. Video coding (video compression) is an essential component for many applications such as high-definition (HD) TV broadcast, video conferencing, mobile services, internet video streaming, HD video storage, and many more. It is the process of converting a digital video into a format that offers efficient video transmission and storage. Advanced Video Coding What is H.264 or Advanced Video Coding?Īdvanced Video Coding (AVC) is the most widely used standard for video coding.
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