3 The MPEG Data Stream
3.1 MPEG-Standards and Applications
In 1992, MPEG-1 was created as the first standard for encoding moving pictures accompanied by sound. The aim was to achieve a picture quality close to that of VHS at CD data rates ( 1.5 Mbit/s). MPEG-1 was provid- ed only for applications on storage media (CD, hard disk) and not for transmission (broadcasting) and its data structures correspond to this ob- jective. The audio and video coding of MPEG-1 is quite close to that of MPEG-2 and all the fundamental algorithms and methods are already in place. There are both I, P and B frames, i.e. forward and backward predic- tion, and naturally there are the DCT-based irrelevance reduction methods already found in JPEG. The picture resolution, however, is limited to about half the VGA resolution (352 x 288). Neither is there any necessity for field encoding (interlaced scanning method). In MPEG-1, there is only the so-called Program Stream (PS) which is composed of multiplexed packet- ized elementary stream (PES) packets of audio and video. The variable- length (64 kbytes max) audio and video PES packets are simply assembled interleaved in accordance with the present data rate to form a data stream.
This data stream is not processed any further since it is only intended to be stored on storage media and not used for transmission. A certain number of audio and video PES packets are combined to form a so-called pack which consists of a header and the payload just like the PES packets themselves.
A pack is often based on the size of a physical data sector of the storage medium.
In MPEG-2, the coding methods were developed further in the direction of higher resolution and better quality. In addition, transmission was also considered, in addition to the storage of such data. The MPEG-2 transport stream is the transportation layer, providing much smaller packet struc- tures and more extensive multiplexing mechanisms. In MPEG-1, there is only one program (only one movie), whereas MPEG-2 can accommodate a multiplexed data stream with up to 20 programs and more.
In addition to Standard Definition TV (SDTV), MPEG-2 also supports High Definition TV (HDTV). MPEG-2 is used throughout the world as digital baseband signal in broadcasting.
A Video CD (VCD) contains an MPEG-1 coded data signal as a pro- gram stream, i.e. there is one program consisting of multiplexed PES packets. The total data rate is about 1.5 Mbit/s. Many pirate copies of mov- ies were available as Video CD and via download from the Internet or bought on the Asian market.
A Super Video CD (SVCD) carries an MPEG-2 data signal coded with 2.4 Mbit/s, also as a program stream with multiplexed PES packets. A Su-
3.1 MPEG-Standards and Applications 37
per Video CD approximately corresponds to VHS type quality, sometimes even better.
On a DVD (Digital Versatile Disk - NOT ‘Digital Video Disk’), the data material is MPEG-2 coded with data rates of up to 10.5 Mbit/s and exhibits a much better picture quality than that recorded on VHS tape. A DVD also carries a multiplexed PES data stream. Subtitles and much else besides are also possible.
The DVD is intended for a variety of applications including video, audio and data. In contrast to the CD (approx. 700 Mbytes), the data volume on a DVD is up to 17 Gbytes and it is possible to have 1, 2 or 4 layers with 4.7 Gbytes each per layer (see table below).
Table 3.1. DVD types
Type Sides Layers /
side Data
[Gbytes] x CD-ROM
DVD 5 1 1 4.7 7
DVD 9 1 2 8.5 13
DVD 10 2 1 9.4 14
DVD 18 2 2 17.1 25
Technical data of the Video DVD:
Storage capacity: 4.7 to 17.1 Gbytes
MPEG-2 Video with variable data rate, 9.8 Mbit/s video max.
Audio:
Linear PCM (LPCM) with 48 kHz or 96 kHz sampling frequen- cy at 16, 20 or 24 bits resolution
MPEG Audio (MUSICAM) mono, stereo, 6-channel sound (5.1), 8-channel sound (7.1)
Dolby Digital (AC3) mono, stereo, 6-channel sound (5.1) Table 3.2. Digital video standards
Standard Video
coding Resolution Video data rate [Mbit/s]
Total data rate [Mbit/s]
MPEG-1 MPEG-1 352 x 288 192 x 144 384 x 288
0.150 - (1.150) - 3.0
max.
approx.
3.5 (1.4112)
MPEG-2 MPEG-2 720 x 576 (SDTV, 25 frames per second) different resolutions up to HDTV
up to 15 basically open, from the interfaces up to 270 MPEG-4 MPEG-4
Part 2 and Part 10 (H.264)
Video CD MPEG-1 352 x 288 1.150 1.4112
Super
VCD MPEG-2 480 x 576 2.4 2.624
Video
DVD MPEG-2 720 x 576 up to 9.8,
variable 10.5
MiniDV MJPEG
variant 720 x 576 25 approx.
30
DVPro MJPEG
variant
720 x 576 25/50 approx.
30/55 Blu-ray
Disc MPEG-2,
MPEG-4 AVC, VC-1
1920 x 1080 (3840 x 2160)
36
Apart from MPEG, there are also proprietary methods based on JPEG all of which have that in common that the video material is only DCT cod- ed and not interframe coded. Both DV and MiniDV are such methods.
MiniDV has been become widely used in the home video camera field and has revolutionized this field with respect to the picture quality. The data rate is 3.6 Mbyte/s total or 25 Mbit/s video data rate. The picture size is 720 x 576 pixels, the same as in MPEG-2, with 25 frames per second.
MiniDV can be edited at any point since it virtually only consists of frames comparable to I frames. DVCPro is the big brother to MiniDV. DVCPro is a studio standard and supports video data rates of 25 and 50 Mbit/s. The 25 Mbit/s data rates corresponds to the MiniDV format. DVCPro and MiniDV are special variants of Motion JPEG. In contrast to MPEG, no quantizer tables are transmitted, neither are quantizer scale factors varied from mac- roblock to macroblock. Instead, a set of quantizing tables is provided local- ly, from which the coder selects the most suitable one from macroblock to macroblock. MiniDV and DVPro exhibit a very good picture quality at relatively high data rates and lend themselves easily to postprocessing.
Home editing software for the PC is available at a cost of around 100 Eu-
3.1 MPEG-Standards and Applications 39
ros and provides functions available only to professionals a few years ago.
Apart from the actual editing, which is now free of losses and is easy to handle, the software also allows video material to be coded in MPEG-1, MPEG-2, VCD, SVCD, video DVD, Blu-ray or just MPEG-4/AVC or HEVC file format.
MPEG-4 was made into a standard in 1999. At the beginning of the new millenium, a further new video compression standard H.264 was devel- oped and standardized. Compared with MPEG-2, this method is more ef- fective by a factor of 2 to 3 and thus allows data rates which are lower by a factor of 2 to 3, often even with improved picture quality. The relevant standard is ITU-T H.264. H.264 has also been incorporated in the group of MPEG-4 standards as MPEG-4 Part 10.
The most important standard documents covered by the heading MPEG- 4 are:
MPEG-4 Part 1 – Systems, ISO/IEC 14496-1
MPEG-4 Part 2 – Video Encoding, ISO/IEC 14496-2
MPEG-4 Part 3 – Audio Encoding, ISO/IEC 14996-3
MPEG-4 Part 10 – H.264 Advanced Video Coding. ISO/IEC 14496-10
MPEG-4 Part 10 – Advanced Video Coding (AVC) is used for HDTV applications in Europe as part of the DVB project. Whereas HDTV re- quires data rates of about 15 Mbit/s for the video signal with MPEG-2, these are about 9 Mbit/s or even lower when they are encoded as MPEG-4 AVC signals.
MPEG-7, in contrast and as a supplement to MPEG-2 and -4, deals ex- clusively with program-associated data, the so-called meta-data, as a com- plement to MPEG-2 and MPEG-4. The aim is to store background infor- mation for a program with the aid of XML- and HTML-based data structures together with the program. MPEG-7 has been a standard since 2001 but has yet to make its debut in practice, at least for the end user.
MPEG-21 was to be transformed into a full standard by 2003 and was intended to contain tools and methods to supplement all other MPEG standards (including end-user-to-end-user applications, e.g. via the Inter- net). It is not clear what has become of it.
After 2010 there are further MPEG-standards published which are no longer named by a number but by a character which are
MPEG-A ISO/IEC 23000
MPEG-B ISO/IEC 23001
MPEG-C ISO/IEC 23002
MPEG-D ISO/IEC 23003
MPEG-E ISO/IEC 23004
MPEG-V ISO/IEC 23005
MPEG-M ISO/IEC 23006
MPEG-U ISO/IEC 23007
MPEG-H ISO/IEC 23008 (HEVC, H.265)
MPEG-DASH ISO/IEC 23009
In 2013 a new video codec – ITU-T H.265 was standardized. This video codec is called HEVC – High Efficiency Video Coding and it was also published as MPEG-H part 2 video. HEVC is now in use for UHDTV ser- vices and in the DVB-T2 network in Germany for HDTV services allow- ing video data rates in the range of about 4 Mbit/s. And last but not least MPEG-DASH was developed for IP streaming applications in OTT ser- vices (“Over the Top TV”).
Table 3.3. MPEG standards
Standard Description Status
MPEG-1 Moving pictures and sound, approx. in VHS quality with CD data rate (< 1.5 Mbit/s)
Standard since 1992
MPEG-2 Digital television
(SDTV+HDTV) Standard since 1993
MPEG-3 Existed only temporarily
(no relation to MP3) not applicable MPEG-4 Multimedia, interactive Standard since 1999 MPEG-7 Program-associated
supplementary data (Meta-data)
Standard since 2001
MPEG-21 Supplementary tools and methods
MPEG-A Futher MPEG standards since approx. 2010 MPEG-B
MPEG-C MPEG-D MPEG-E MPEG-V MPEG-U
MPEG-H MPEG-H, part 2 HEVC
see also H.265 Standard since 2013 MPEG-
DASH
“Dynamic Adaptive Streaming over HTTP (DASH)”
Standard since 2012