MPEG-2

MPEG-2 extends MPEG-1 to cover a wider range of applications. The primary application targeted during the definition process was all-digital transmission of broadcast-quality video at bit-rates of 4–9 Mbps. However, MPEG-2 is useful for many other applications, such as HDTV, and now supports bit-rates of 1.5–60 Mbps.

MPEG-2 is an ISO standard (ISO/IEC 13818), and consists of eleven parts:

 

Systems	ISO/IEC 13818–1
Video	ISO/IEC 13818–2
Audio	ISO/IEC 13818–3
Conformance testing	ISO/IEC 13818–4
Software simulation	ISO/IEC 13818–5
DSM-CC extensions	ISO/IEC 13818–6
Advanced audio coding	ISO/IEC 13818–7
RTI extension	ISO/IEC 13818–9
DSM-CC conformance	ISO/IEC 13818–10
IPMP	ISO/IEC 13818–11

As with MPEG-1, the compressed bitstreams implicitly define the decompression algorithms. The compression algorithms are up to the individual manufacturers, within the scope of an international standard.

The Digital Storage Media Command and Control (DSM-CC) extension (ISO/IEC 13818–6) is a toolkit for developing control channels associated with MPEG-2 streams. In addition to providing VCR-type features such as fast-forward, rewind, pause, etc., it may be used for a wide variety of other purposes, such as packet data transport. DSM-CC works in conjunction with next-generation packet networks, working alongside Internet protocols as RSVP, RTSP, RTP, and SCP.

The Real Time Interface (RTI) extension (ISO/IEC 13818-9) defines a common interface point to which terminal equipment manufacturers and network operators can design. RTI specifies a delivery model for the bytes of an MPEG-2 System stream at the input of a real decoder, whereas MPEG-2 System defines an idealized byte delivery schedule.

IPMP (Intellectual Property Management and Protection) is a digital rights management (DRM) standard, adapted from the MPEG-4 IPMP extension specification. Rather than a complete system, a variety of functions are provided within a framework.

Audio Overview

In addition to the non-backwards-compatible audio extension (ISO/IEC 13818–7), MPEG-2 supports up to five full-bandwidth channels compatible with MPEG-1 audio coding. It also extends the coding of MPEG-1 audio to half sampling rates (16 kHz, 22.05 kHz, and 24 kHz) for improved quality for bit-rates at or below 64 kbps per channel.

Insider Info

MPEG-2.5 is an unofficial, yet common, extension to the audio capabilities of MPEG-2. It adds sampling rates of 8 kHz, 11.025 kHz, and 12 kHz.

Video Overview

With MPEG-2, profiles specify the syntax (i.e., algorithms) and levels specify various parameters (resolution, frame rate, bit-rate, etc.). Main Profile@Main Level is targeted for SDTV applications, while Main Profile@High Level is targeted for HDTV applications.

Levels

MPEG-2 supports four levels, which specify resolution, frame rate, coded bit-rate, and so on for a given profile.

Low Level (LL)

MPEG-1 Constrained Parameters Bit-stream (CPB), supporting up to 352×288 at up to 30 frames per second. Maximum bit-rate is 4 Mbps.

Main Level (ML)

MPEG-2 Constrained Parameters Bit-stream (CPB) supports up to 720×576 at up to 30 frames per second and is intended for SDTV applications. Maximum bit-rate is 15–20 Mbps.

High 1440 Level

This level supports up to 1440×1088 at up to 60 frames per second and is intended for HDTV applications. Maximum bit-rate is 60–80 Mbps.

High Level (HL)

High Level supports up to 1920×1088 at up to 60 frames per second and is intended for HDTV applications. Maximum bit-rate is 80–100 Mbps.

Profiles

MPEG-2 supports six profiles, which specify which coding syntax (algorithms) is used. Tables 7.3 through 7.10 illustrate the various combinations of levels and profiles allowed.

Table 7.3. MPEG-2 Acceptable Combinations of Levels and Profiles

Level	Profile
	Nonscalable				Scalable
	Simple	Main	Multiview	4:2:2	SNR	Spatial	High
High	–	yes	–	yes	–	–	yes
High 1440	–	yes	–	–	–	yes	yes
Main	yes	yes	yes	yes	yes	–	yes
Low	–	yes	–	–	yes	–	–

Table 7.4. Some MPEG-2 Profile Constraints

Constraint	Profile
	Nonscalable				Scalable
	Simple	Main	Multiview	4:2:2	SNR	Spatial	High
Chroma format	4:2:0	4:2:0	4:2:0	4:2:0 or 4:2:2	4:2:0	4:2:0	4:2:0 or 4:2:2
Picture types	I, P	I, P, B	I, P, B	I, P, B	I, P, B	I, P, B	I, P, B
Scalable modes	–	–	Temporal	–	SNR	SNR or Spatial	SNR or Spatial
Intra dc precision (bits)	8, 9, 10	8, 9, 10	8, 9, 10	8,9,10,11	8,9,10	8,9,10	8,9,10,11
Sequence scalable extension	no	no	yes	no	yes	yes	yes
Picture spatial scalable extension	no	no	no	no	no	yes	yes
Picture temporal scalable extension	no	no	yes	no	no	no	no
Repeat first field		constrained	unconstrained	constrained		unconstrained

Table 7.5. MPEG-2 Number of Permissible Layers for Scalable Profiles

Level	Maximum Number of Layers	Profile
		SNR	Spatial	High	Multiview
High	All layers (base+enhancement)	–	–	3	2
	Spatial enhancement layers			1	0
	SNR enhancement layers			1	0
	Temporal auxiliary layers			0	1
High 1440	All layers (base+enhancement)	–	3	3	2
	Spatial enhancement layers		1	1	0
	SNR enhancement layers		1	1	0
	Temporal auxiliary layers		0	0	1
Main	All layers (base+enhancement)	2	–	3	2
	Spatial enhancement layers	0		1	0
	SNR enhancement layers	1		1	0
	Temporal auxiliary layers	0		0	1
Low	All layers (base+enhancement)	2	–	–	2
	Spatial enhancement layers	0			0
	SNR enhancement layers	1			0
	Temporal auxiliary layers	0			1

Table 7.6. Some MPEG-2 Video Decoder Requirements for Various Profiles

Profile	Profile			Profile at Level for Base Decoder
	Base Layer	Enhancement Layer 1	Enhancement Layer 2
SNR	4:2:0	SNR, 4:2:0	–	MP@same level
Spatial	4:2:0	SNR, 4:2:0	–	MP@same level
	4:2:0	Spatial, 4:2:0	–	MP@(level–1)
	4:2:0	SNR, 4:2:0	Spatial, 4:2:0
	4:2:0	Spatial, 4:2:0	SNR, 4:2:0
High	4:2:0 or 4:2:2	–	–	MP@same level
	4:2:0	SNR, 4:2:0	–
	4:2:0 or 4:2:2	SNR, 4:2:2	–	HP@ (level–1)
	4:2:0	Spatial, 4:2:0	–
	4:2:0 or 4:2:2	Spatial, 4:2:2	–
	4:2:0	SNR, 4:2:0	Spatial, 4:2:0 or 4:2:2
	4:2:0 or 4:2:2	SNR, 4:2:2	Spatial, 4:2:2
	4:2:0	Spatial, 4:2:0	SNR, 4:2:0 or 4:2:2
	4:2:0	Spatial, 4:2:2	SNR, 4:2:2
	4:2:2	Spatial, 4:2:2	SNR, 4:2:2
Multiview	4:2:0	Temporal, 4:2:0	–	MP@same level

Table 7.7. MPEG-2 Upper Limits of Resolution and Temporal Parameters. In the case of single layer or SNR scalability coding, the “Enhancement Layer” parameters apply

Level	Spatial Resolution Layer	Parameter	Profile
			Simple	Main	Multiview	4:2:2	SNR / Spatial	High
High	Enhancement	Samples per line	–	1920	1920	1920	–	1920
		Lines per frame		1088	1088	1088		1088
		Frames per second		60	60	60		60
	Lower	Samples per line	–	–	1920	–	–	960
		Lines per frame			1088			576
		Frames per second			60			30
High 1440	Enhancement	Samples per line	–	1440	1440	–	1440	1440
		Lines per frame		1088	1088		1088	1088
		Frames per second		60	60		60	60
	Lower	Samples per line	–	–	1440	–	720	720
		Lines per frame			1088		576	576
		Frames per second			60		30	30
Main	Enhancement	Samples per line	720	720	720	720	720	720
		Lines per frame	576	576	576	608	576	576
		Frames per second	30	30	30	30	30	30
	Lower	Samples per line	–	–	720	–	–	352
		Lines per frame			576			288
		Frames per second			30			30
Low	Enhancement	Samples per line	–	352	352	–	352	–
		Lines per frame		288	288		288
		Frames per second		30	30		30
	Lower	Samples per line	–	–	352	–	–	–
		Lines per frame			288
		Frames per second			30

Note: 1. The above levels and profiles that originally specified 1152 maximum lines per frame were changed to 1088 lines per frame.

Table 7.8. Example Levels and Resolutions for MPEG-2 Main Profile

Level	Maximum Bit-Rate (Mbps)	Typical Active Resolutions	Frame Rate (Hz)2
			23.976p	24p	25p	29.97p	30p	50p	59.94p	60p	25i	29.97i	30i
High	80	1920×10801	×	×	×	×	×				×	×	×
	(100 for High Profile) (300 for 4:2:2 Profile)
High 1440	60	1280×720	×	×	×	×	×	×	×	×
	(80 for High Profile)	960×10801	×	×	×	×	×				×	×	×
		1280×10801	×	×	×	×	×				×	×	×
		1440×10801	×	×	×	×	×				×	×	×
Main	15	352×480	×	×		×	×		×	×		×	×
	(20 for High Profile) (50 for 4:2:2 Profile)	352×576		×	×			×			×
		480×480	×	×		×	×		×	×		×	×
		544×480	×	×		×	×		×	×		×	×
		544×576		×	×			×			×
		640×480	×	×		×	×		×	×		×	×
		704×480,	×	×		×	×		×	×		×	×
		720×480
		704×576,		×	×			×			×
		720×576
Low	4	320×240	×	×		×	×		×	×		×	×
		352×240	×	×		×	×		×	×		×	×
		352×288		×	×			×			×

Notes: 1. The video coding system requires that the number of active scan lines be a multiple of 32 for interlaced pictures, and a multiple of 16 for progressive pictures. Thus, for the 1080-line inter-laced format, the video encoder and decoder must actually use 1088 lines. The extra eight lines are “dummy” lines having no content, and designers choose dummy data that simplifies the implementation. The extra eight lines are always the last eight lines of the encoded image. These dummy lines do not carry useful information, but add little to the data required for transmission.

2. p=progressive; i=interlaced.

Table 7.9. MPEG-2 Upper Limits for Y Sample Rate (M samples/second). In the case of single layer or SNR scalability coding, the “Enhancement Layer” parameters apply

Level	Spatial Resolution Layer	Profile
		Simple	Main	Multiview	SNR / Spatial	High	4:2:2
High	Enhancement	–	62.668800	62.668800	–	62.668800 (4:2:2)83.558400 (4:2:0)	62.668800
	Lower	–	–	62.668800	–	14.745600 (4:2:2)19.660800 (4:2:0)	–
High 1440	Enhancement	–	47.001600	47.001600	47.001600	47.001600 (4:2:2)62.668800 (4:2:0)	–
	Lower	–	–	47.001600	10.368000	11.059200 (4:2:2)14.745600 (4:2:0)	–
Main	Enhancement	10.368000	10.368000	10.368000	10.368000	11.059200 (4:2:2)14.745600 (4:2:0)	11.059200
	Lower	–	–	10.368000	–	3.041280 (4:2:0)	–
Low	Enhancement	–	3.041280	3.041280	3.041280	–	–
	Lower	–	–	3.041280	–	–	–

Table 7.10. MPEG-2 Upper Limits for Bit-Rates (Mbps)

Level	Profile
	Nonscalable				Scalable
	Simple	Main	Multiview	4:2:2	SNR/Spatial	High
High	–	80	130 (both layers)	300	–	100 (all layers)
			80 (base layer)			80 (middle+base layers)
						25 (base layer)
High 1440	–	60	100 (both layers)	–	60 (all layers)	80 (all layers)
			60 (base layer)		40 (middle+base layers)	60 (middle+base layers)
					15 (base layer)	20 (base layer)
Main	15	15	25 (both layers)	50	15 (both layers)	20 (all layers)
			5 (base layer)		10 (base layer)	15 (middle+base layers)
						4 (base layer)
Low	–	4	8 (both layers)	–	4 (both layers)	–
			4 (base layer)		3 (base layer)

Simple Profile (SP)

Main profile without the B frames, intended for software applications and perhaps digital cable TV.

Main Profile (MP)

Supported by most MPEG-2 decoder chips, it should satisfy 90% of the consumer SDTV and HDTV applications. Typical resolutions are shown in Table 7.8.

Multiview Profile (MVP)

By using existing MPEG-2 tools, it is possible to encode video from two cameras shooting the same scene with a small angle difference.

4:2:2 Profile (422P)

Previously known as “studio profile,” this profile uses 4:2:2 YCbCr instead of 4:2:0, and with main level, increases the maximum bit-rate up to 50 Mbps (300 Mbps with high level). It was added to support pro-video SDTV and HDTV requirements.

SNR and Spatial Profiles

Adds support for SNR scalability and/or spatial scalability.

High Profile (HP)

Targeted for pro-video HDTV applications.