DVD adds many additional restrictions to the popular compliance parameter sets of MPEG. One good example is the restriction on the coded size of a picture: MPEG-2 Main Profile @ Main Level allows any coded frame size between 16 and 720 pixels horizontally and 16 and 576 pixels vertically. DVD, however, restricts the coded frame sizes to a very limited but practical subset.
In MPEG, audio can be coded at a sample rate of 32, 44.1 or 48 kHz. In DVD, the rates of both Dolby AC-3 and MPEG audio are strictly set to 48 kHz.
MPEG is a generic representation meant for a wide variety of applications. DVD has taken a practical subset to promote interoperability by simplifying implementations and insuring features (such as random accessibility).
|Coded representation||MPEG-1 (SIF combo)|
MPEG-2 (Main Profile @ Main Level)
|Frame rate||29.97 or 25 Hz|
|TV system||525/60 or 625/50|
|Aspect ratio||4:3 (all video formats)|
16:9 (all formats except 352 pixels/line)
|Display Mode||pan & scan, letterbox|
|Coded frame sizes||525/60: 720x480, 704x480, 352x480, 352x240|
625/50: 720x576, 704x576, 352x576, 352x288
(MPEG-1 is allowed only in 352x240 or 352x288 res).
|GOP size||max 36 fields or 18 frames (NTSC)|
max 30 fields or 15 frames (PAL)
|Buffer size||1.8535008 Mbits (MPEG-2)|
max 327689 bits (MPEG-1)
|Transfer method||VBR, CBR (MPEG-2)|
only CBR for MPEG-1
|Maximum bitrate||9.8 Mbit/sec|
|Low_delay||NOT permitted !!!!|
the frame rate is the intended display frame rate. The number of coded frames in a sequence may vary due to 3:2 pulldown (the DVD MPEG decoder performs this function). The permitted values in DVD are more restrictive than MPEG-2 MP@ML which also includes 23.976, 24, and 30 frames/sec rates.
aspect ratio is the display aspect ratio. Only 16:9 and 4:3 are permitted. Note: MP@ML's 2.21:1 is not included.
MP@ML has no GOP size restriction. In fact, the GOP() is considered to be an insignificant layer in MPEG-2. Instead the sequence() layer serves as the most important boundary in the generic MPEG sense.
The MPEG-1 and MPEG-2 vbv_buffer_size limits are the same as MP@ML and Constrained Parameters Bitstreams, respectively.
The maximum bitrate of 9.8 Mbit/sec is more restrictive than MP@ML's 15 Mbit/sec limit. However, the point of diminishing returns (no visual difference between original video and compressed video) is widely known to be around 9 Mbit/sec.
user_data() fields in MPEG video picture headers contain closed captioning (similar to Grand Alliance and DVB methods). See this ATSC (Advanced Television Systems Committee) site for more information: http://www.atsc.org/
[is this the same in DVB, DVD, and ATSC ? ]
For picture sizes, only a very limited set of coded dimensions are legal.
Variable bit rate is permitted only in MPEG-2 streams since the VBV model in MPEG-2 has provisions for it. MPEG-1 was an earlier standard (by two years) and not developed the VBV model to handle 3:2 pulldown cases.
contrary to popular belief: all DVD players are required to decode video streams up to 9.8 Mbit/sec for indefinite periods of time. The popular average rate of 3.5 Mbit/sec or 4.7 Mbit/sec are merely canonical figures created by the notion that only single sided, single layer discs will hold feature length films. Should Single Sided, Double Layer discs prevail, the average rate would be almost twice as great. ALL DVD PLAYERS MUST SUSTAIN A 9.8 MBIT/SEC VIDEO DECODE RATE!!!!!!! Hardwired (Application Specific Integrated Circuits---ASICs) implementations of MPEG-2 MP@ML decoders are generally capable of handling 15 mbit/sec sustained rates.
MPEG-2 video decoder chips have implemented pan & scan for a few years already since it has been a requirement for cable TV and direct broadcast satellite applications. The letterbox requirement (vertical filter) is a relatively new addition to the MPEG decoder universe. The second generation DVD MPEG-2 video decoders will most likely perform "on-chip" sub-picture reconstruction.
|Display 4:3||Display 16:9|
|Source 4:3||No conversion||horizontal filtering accomplished by TV monitor.|
|Source 16:9||letterbox (vertical filter) or Pan & Scan||No conversion|
Note: Letterbox Conversion is a mandatory feature in the DVD Player !!!