Articles by YF

  1. x264 Adaptive Quant

    Wed 06 December 2017
    By YF

    Outline


    Adaptive Quant is claimed as the biggest performance improvement of x264 optimization history. According to AQ's author Jason Garrett-Glaser's explaination variance-based adaptive quantization

    The (very rough) intuitive justification works something like this. Imagine every macroblock has just one frequency coefficient.  This coefficient can be big or small.
    
    If a …
    Tagged as : Video Codec x264
  2. x264 Slice Type Decision

    Wed 06 December 2017
    By YF

    Outline


    Doc of MB Tree

    Process


    The x264 decide slice type in a GOP structure unit, which include one reference frame (I,P) and no / several non-reference frame (B). The processed frame will be shift out frame lookahead frame list and put into frame's current list.

    if( !h->frames.current …
    Tagged as : Video Codec x264
  3. x264 Rate Control

    Tue 05 December 2017
    By YF

    Outline


    Rate control allows selection of encoding parameters to maximize quality under the constraint imposed by specified bitrate and decoder video buffer. The rate control in H.264/AVC can be performed at three different granularities – group of pictures level, picture level and macroblocks level. At each level, the rate …

    Tagged as : Video Codec x264
  4. H264 De-blocking Filter

    Mon 20 November 2017
    By YF

    Introduction


    A deblocking filter is a video filter applied to decoded compressed video to improve visual quality and prediction performance by smoothing the sharp edges which can form between macroblocks when block coding techniques are used. Here is an artical and web page introduce the H264 in-loop filter.

    Description of …

    Tagged as : Video Codec h264
  5. H264 Entropy Coding

    Mon 20 November 2017
    By YF

    Introduction


    The entropy coding is another very important part of video coding. The purpose of entorpy coding is to compress the syntax data, residual pixel data. The h264 standard specifies two types of entropy coding: Context-based Adaptive Binary Arithmetic Coding (CABAC) and Variable-Length Coding (VLC)

    Variable Length Coding (VLC)


    • Exp-Golomb …
    Tagged as : Video Codec h264
  6. H264 Motion Estimation & Inter Prediction

    Mon 20 November 2017
    By YF

    Introduction


    Inter prediction creates a prediction model from one or more previously encoded video frames. The model is formed by shifting samples in the reference frame(s) (motion compensated prediction). The AVC CODEC uses block-based motion compensation, the same principle adopted by every major coding standard since H.261. Important …

    Tagged as : Video Codec h264
  7. H264 Intra Prediction

    Mon 20 November 2017
    By YF

    Introduction


    The purpose of intra prediction is to eliminate the space relationship of current picture. Before H264, there are almost no 'modern' intra prediction. Usually use DC prediction (MPEG2/MPEG4) and AC prediction (MPEG4) to act as intra prediction. Another purpose of intra prediction is that he prediction process does …

    Tagged as : Video Codec h264
  8. H264 Transform, Quant & Dequant Algorithm

    Mon 20 November 2017
    By YF

    Introduction


    Each residual macroblock is transformed, quantized and coded. Previous standards such as MPEG-1, MPEG-2, MPEG-4 and H.263 made use of the 8x8 Discrete Cosine Transform (DCT) as the basic transform. The “baseline” profile of H.264 uses three transforms depending on the type of residual data that is …

    Tagged as : Video Codec h264
  9. x264 Encoder Open

    Mon 20 November 2017
    By YF

    Outline


    In this chapter, we make a brief review of `x264_encoder_open' function. In this function, x264 mainly did several jobs like

    x264_threading_init                             // initial thread
    x264_validate_parameters                        // validate the configure parameters
    x264_sps_init                                   // initial sps parameters
    x264_pps_init                                   // initial pps parameters
    x264_cqm_init                                   // quant & dequant parameters initial
    Init frames parameters, such as max reference numbers …
    Tagged as : Video Codec x264

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