H264 Nonsense I Hate This

Question 1

ITU - T

Answer 1

Intl Telecommunications Unit - telecommunications standardization sector

Defines the H-series recommendations which relate to audiovisual and multimedia systems

Divided into working groups like VCEG

Question 2

VCEG

Answer 2

Visual coding experts group

ITU working group responsible for the h264 and h265

Question 3

JCT-VC

Answer 3

Joint collaborative team on video coding

Collab between MPEG and VCEG

Question 4

Profiles

Answer 4

Define a set of encoding tools and algorithms available to the encoder

Related to H264/AVC standards

Question 5

H264 level

Answer 5

A specified set of constraints that indicate a degree of required decoder performance for a profile

A level of support within a profile specified the max picture resolution, frame rate, and bit rate that a decoder may use; a decoder that conforms to a given level must be able to decode all bitstreams encoded for that level and all lower levels

Question 6

H264 workflow

Answer 6

Color transform
Subsample cb, cr
Partition
Predict partition blocks (inter/intra)
Calculate residual from actual and predicted frame
Transform residual to frequency domain
Quantize transformed residual
Deblock filter
Entropy encoding
Compressed frame

Question 7

Subsampling

Answer 7

Sampling of cb and cr channels into smaller amounts of data

4:2:0 subsampling in h264 is most common; 4:2:2 and 4:4:4 are also available

Question 8

Partition

Answer 8

H264 divides frames into 16x16 macroblocks, which are divided into prediction blocks for inter/intra prediction

High frequency areas are divided into 4x4 prediction blocks

Question 9

Intra prediction

Answer 9

Used when frame being encoded is an I-frame/slice

Means pixel values will be calculated from surrounding pixel values already decoded within the frame

Question 10

How is the intra mode of prediction decided?

Answer 10

Modes are calculated and compared to the macro lock being encoded

Comparison is done by subtracting the predicted macroblock from the actual macroblock

The Sum of Absolute Differences for each method is compared and the method with the lowest SAD is used

Question 11

Residual

Answer 11

Calculated by subtracting the predicted from the actual block being encoded

(Prediction mode and residual are stored)

Question 12

Decoding

Answer 12

The block is reproduced by predicting the block from the decoded macroblocks already decoded and adding the residual

Question 13

Interprediction

Answer 13

Used for p and b frames

Requires motion estimation and motion compensation

Instead of recording motion vectors, only the differences are recorded

Question 14

MVD

Answer 14

Motion vector differential

The difference between an actual motion vector and the predicted motion vector, stored instead of the motion vectors to save data

Question 15

Transform to frequency domain

Answer 15

Integer approximation of the Discrete Cosine Transform used transform residual luminance info to frequency info

Question 16

Quantization

Answer 16

Dividing and rounding residual information

Question 17

Entropy encoding

Answer 17

H264 standard allows use of CAVLC and CABAC

Question 18

Entropy encoding

Answer 18

H264 standard allows use of CAVLC and CABAC