H.264 / MPEG-4 Part 10

Nimrod Peleg

March 2003

Encoder

..image sequence

0101...

bit stream+

DCT Q VLC

Q-1

DCT-1

+

MEMM.C.

-

+

Intra / Interswitch

++

M.E.

Encoder

..image sequence

0101...

bit stream+

DCT Q VLC

Q-1

DCT-1

+

MEMM.C.

-

+

Intra / Interswitch

++

M.E.

Encoder

..image sequence

0101...

bit stream+

DCT Q VLC

Q-1

DCT-1

+

MEMM.C.

-

+

Intra / Interswitch

++

M.E.

Encoder

..image sequence

0101...

bit stream+

DCT Q VLC

Q-1

DCT-1

+

MEMM.C.

-

+

Intra / Interswitch

++

M.E.

Encoder

..image sequence

0101...

bit stream+

DCT Q VLC

Q-1

DCT-1

+

MEMM.C.

-

+

Intra / Interswitch

++

M.E.

Previous Standards

H.264 Brief review

• Goal– Develop a high-performance video coding standard.

• Start from zero.• No backward compatibility.• Assumptions

– Block based.– Software implementation.– Network friendly.

H.264 Encoder

0101...

bit stream

+IDCT Q

EntropyCoder

Q-1

IDCT -1

+

FramesStoreM.C.

-

+

Intra/InterSwitch

++

M.E.

..Image sequence

Coding control

Transform

• DCT like.

• Integer arithmetic only.– without multiplications.

• Optional use of a 4x4 transform block size.

Quantization

• Compounding quantization step.

• Thirty-two different quantization step sizes.– The step sizes are increased at a compounding rate

of approximately 12.5%.

• Different quantizer for luminance, chrominance.

• Two different coefficient-scanning patterns.– The simple zigzag scan.– The double scan.

Frames Store

• The H.264 standard offers the option of having multiple reference frames in inter picture coding.

• Up to five different reference frames could be selected.– Resulting in better subjective video quality and more

efficient coding of the video frame under consideration.

• Using multiple reference frames might help making the H.264 bit-stream error resilient.

Motion Estimation & Compensation

• Motion Estimation is where H.264 makes most of its gains in coding efficiency.

• Quarter pixel accurate motion compensation.

• Translation only.

• The standard does not determine which algorithm should be used.

Motion Estimation & Compensation

• Seven optional modes.

Different modes of dividing a macroblock for motion estimation in H.264

Entropy Coding

• H.264 has adopted two approaches for entropy coding :– Universal Variable Length Codes (UVLCs)

• One table.

– Context-Based Adaptive Binary Arithmetic Coding (CABAC)

Intra prediction

• 9 optional prediction modes for each 4x4 luma block.

• 4 optional modes for a 16x16 luma block.

• 4 optional prediction modes for a 8x8 chroma component.

• One mode for 4x4 chroma block.

Summery

• Transform – IDCT– Optional use of a 4x4 transform block size.

• Quantizer– step sizes are increased at a compounding rate of approximately

12.5%.– Two coefficient-scanning patterns.

• Motion estimation and compensation– Translation only.– A number of different block sizes are used for motion prediction.– Quarter pixel positions are used for motion prediction.

Summery

• Frames store– Multiple reference frames may be used for

prediction.

• Entropy coding– Only one regular VLC is used for symbol

coding.