Video Coding Fundamentals

Video Compression

• Compression is the act or process of compacting data into a smaller number of bits.
• Video compression (video coding) is the process of converting digital video into a format suitable for transmission or storage, whilst typically reducing the number of bits.
• Compression involves a complementary pair of systems, a compressor (encoder) and a decompressor (decoder).
• Data compression is achieved by removing redundancy, i.e. components that are not necessary
• for faithful reproduction of the data.
• Most video coding methods exploit both temporal and spatial redundancy to achieve compression.
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• Bildunterschrift: Encoder/Decoder Pair

Prediction Model

• The goal of the prediction model is to reduce redundancy by forming a prediction of the data and subtracting this prediction from the current data.
• The prediction may be formed from previously coded frames (a temporal prediction) or from previously coded image samples in the same frame (a spatial prediction).
• Temporal Prediction:
• prediction from the previous video frame: The simplest method of temporal prediction is to use the previous frame as the predictor for
• the current frame
• Motion estimation and compensation
• Block based
• sub pixel based​​​​​​​

Block-Based Motion Estimation

• The method of motion compensation is to compensate for movement of rectangular sections or ‘blocks’ of the current frame.
• Procedure for motion estimation:
• It is carried out for all MxN blocks
• Search an area in the reference frame, past or future frame, to find a similar MxN-sample region.
• The chosen candidate region becomes the predictor for the current MxN block (a motion compensated prediction) and is subtracted from the current block to form a residual MxN block (motion compensation).
• The residual block is encoded and transmitted and the offset between the current block and the position of the candidate region (motion vector) is also transmitted.
• Types of M

Prediction Model

• Spatial model: intra prediction
• The prediction for the current block of image samples is created from previously-coded
• samples in the same frame
• Assuming that the blocks of image samples are coded in raster-scan order,
• which is not always the case, the upper/left shaded blocks are available for intra prediction.
• Once the prediction has been generated, it is subtracted from the current block to form a residual in a similar way to inter prediction.
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• Bildunterschrift: Intra Prediction