Mpeg 4

What is the difference between intra and inter pictures in video coding?

Intra pictures are coded independently without reference to past pictures, while inter pictures are obtained by subtracting a motion-compensated prediction from the original picture.

How are residuals processed in video coding?

Residuals are transformed into the frequency domain, scanned, quantized, and encoded using variable-length codes.

What is the structure of a macroblock in the H.264 standard?

Each macroblock consists of four 8 × 8 luminance blocks and two chrominance blocks.

What additional partitions are allowed in H.264 macroblocks compared to previous standards?

H.264 allows macroblock partitions to be subdivided into 8×4, 4×8, and 4×4 sizes.

What does motion-compensated prediction help with in video compression?

It helps track finer details in video frames, leading to better prediction and lower bit rates.

Why does using smaller blocks in motion-compensated prediction increase bit rates?

Smaller blocks require more motion vectors to be encoded and transmitted, consuming more bit resources.

How does H.264 enhance prediction accuracy?

It uses smaller block sizes in active regions and larger block sizes in stationary areas.

What is the pixel accuracy used for motion compensation in H.264?

Motion compensation is accomplished with quarter-pixel accuracy.

How does H.264 handle reference pictures during motion compensation?

The selection of reference pictures is done at the macroblock partition level, with all sub-macroblock partitions using the same reference.

What is a Pskip type macroblock in H.264?

A Pskip macroblock uses 16×16 motion compensation where the prediction error is not transmitted, useful for low change regions.

What kind of transform does H.264 utilize instead of an 8 × 8 DCT?

H.264 uses a 4 × 4 integer DCT-like transform matrix.

What is a disadvantage of the integer transform in H.264?

The product of the forward and inverse transforms does not result in the identity matrix.

How is the discrepancy in the transform compensated for in H.264?

By the use of scale factors during quantization.

What is one advantage of using a smaller integer transform in video coding?

It simplifies implementation and avoids error accumulation during the transform process.

What effect does a smaller block size have on video data representation?

It allows better representation of small stationary regions and minimizes ringing effects during sharp transitions.

What is the importance of motion vectors in video coding?

Motion vectors indicate the direction and speed of motion in a scene, affecting the accuracy of predictions.

What enhancements are made to the prediction process in H.264?

Filters on the four block edges are used to enhance the prediction process.

What are the dimensions of the H.264 transform matrix used?

The transform matrix used is a 4 × 4 integer DCT-like matrix.

What happens if motion vectors consume too many bits in encoding?

The overall bit rate increases, potentially reducing the efficiency of the compression.

How does H.264 deal with diverse motion in a video scene?

It uses a variety of block sizes and shapes for motion compensation, allowing for better tracking.

What role do quantization and coding play in the encoding process of H.264?

Quantization reduces the precision of the transform coefficients to ease encoding, while variable-length coding compresses the data for efficient storage.