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mpeg2:mpeg2_elementary_stream_structure

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MPEG-2 Elementary Video

  1. stream structure
  2. Sequence headers
  3. Sequence Extension
  4. Sequence Display Extension
  5. Quant Matrix Extension
  6. Copyright extension
  7. Sequence Scalable Extension
  8. Group of Pictures
  9. Picture headers
  10. Picture Display Extension
  11. Picture Coding Extension
  12. Slice

The structure differs from that of MPEG-1 elementary video in terms of the possible extensions and, in the case of the TMPG encoder, the number of slices.

MPEG-2 Elementary Video

stream structure

Structure of an MPEG-2 program stream.

 

video streaming:

Sequence Sequence ... Sequence

 
The video stream consists of several consecutive sequences.

 

Sequence:

Sequence
start code		 video
parameters		 bitstream
parameters		 QT's,
Misc		 Group of
Picture		 ... Group of
Picture		 Sequence
end code

 
The sequence can or should contain further sequence headers. Usually before each Group of Picture (GOP). The sequence headers are needed for creating entry points (chapter markers) and for fast scrolling. At the end there should be a sequence decode. However, this does not seem to be common with MPEG-2.

 

Group of Picture (GOP):

GOP
start code		 timecode
_		 GOP
params		 Picture ... Picture

 
The GOP contains the different picture types. There are I, P, B and D frames.

Intra picture (I-frames) are full images. Predicted picture (P frames) are partial pictures and refer to the previous I/P frames. Bidirectional pictures (B frames) are also partial pictures and refer to the preceding and following I/B frame. Direct Coded Picture (D-Frames) are not used in MPEG-2.

 

Picture:

Picture
start code		 Type buffer
params		 Encode
Params		 Slice ... Slice

 
The order of the images does not correspond to the order in which they are displayed. The images are composed of slices.

 

Slice:

Slice
start code		 Vertical
position		 QScale macro block ... macro block

 
Slices are a vertical and horizontal aggregation of macroblocks.

 

macro block:

Address
Increment		 Type Motion
Vector		 QScale CBP b0 ... b5

 
A macroblock comprises an image section with a total of 16x16 picture elements (pixels). It stores the YUV 4:2:0 (YCbCr) color information. The Y components of all pixels are contained in the first four blocks b0 to b3. In the fifth block b4, the blue chrominance values ​​(Cb) are stored in one point for each 4 pixels. The corresponding red chrominance values ​​(Cr) are in the sixth block b5.

MPEG-2 Elementary Video

Sequence headers

Each header starts with the PACK_START_CODE_PREFIX, which consists of the three bytes 0, 0 and 1. As a hexadecimal number, it is represented as $000001. This is followed by the ID. For the sequence header, this is the value $B3. The length of the header has different lengths according to the matrices used.

Each sequence header represents a possible entry point. This means that a chapter can only be created where there is a sequence header.

It should also happen that sequence headers are not marked with $000001B3 but with $000000B3.

Construction

  1. 4 bytes: SEQUENCE_HEADER_CODE = $000001B3
  2. 12 Bit: Width - Image width in pixels
  3. 12 Bit: Height - image height in pixels
  4. 4 bit: Aspect Ratio - aspect ratio
  5. 4 bit: frame rate - refresh rate
  6. 18 bit: bit rate
  7. 1 bit: markers
  8. 10 bits: VBV
  9. 1 bit: Constrained parameter flag
  10. 1 bit: load intra matrix (0) or standard (1)?
  11. 64 bytes: Intra matrix if non-standard matrix is ​​used.
  12. 1 Bit: Load Non Intra Matrix (0) or Standard (1)?
  13. 64 bytes: Non Intra Matrix, unless Standard Matrix is ​​used.

As a scheme:

  7 6 5 4 3 2 1 0
0 SEQUENCE_HEADER_CODE
1
2
3
4 image width
5 nor image width image height
6 nor image height
7 aspect ratio frame rate
8th bitrate
9 nor bitrate
10 nor bitrate marker VBV
11 VBV CPF Load? IN THE
12 still intra matrix
...
75 still intra matrix Load?
76 Non intra matrix
...
139

 
The MPEG type can only be taken directly from the sequence header if the aspect ratio has a value above 4. But then it is an MPEG-1 video.

 

Explanations

The values ​​for the aspect ratio:

value Aspect ratio text
0 'forbidden'
1 1:1 square pixels
2 4:3 screen
3 16:9 screen
4 2.21:1 display
5-15 'reserved'

 

The values ​​for the frame rate (refresh rate):

value Frame rate number Frame rate text
0 0 'forbidden'
1 24000/1001.0 '23.976 fps -- NTSC encapsulated film rate'
2 24.0 'Standard international cinema film rate'
3 25.0 'PAL (625/50) video frame rate'
4 30000/1001.0 '29.97 -- NTSC video frame rate'
5 30.0 'NTSC drop-frame (525/60) video frame rate'
6 50.0 'double frame rate/progressive PAL'
7 60000/1001.0 'double frame rate NTSC'
8th 60.0 'double frame rate drop frame NTSC'
9-15 0 'reserved'

 

The bit rate is given in 400 bits per second. The value $3FFFF is supposed to mean a variable bitrate. In the test, TMPGEnc and CCEB each indicated the maximum bit rate there.

The marker bit is intended to detect errors. It must always have the value 1.

The VBV is the memory required to decode the images. It is specified in 16 kB blocks.

The constrained parameter flag is always set to 0 here. The TMPG Encoder 2.5* uses the 10 bits for the VBV and the bit of the constrained parameter flag for the VBV specification, so that only half of the VBV is displayed here.

The intra or non intra matrix load bit indicates whether the standard matrix is ​​used or whether the corresponding matrix is ​​saved at this point and must be loaded. The matrix is ​​stored in Zig Zag Scan.

 

extensions

At least one extension follows the sequence header. An MPEG-2 is identified via this. The ID of the extension is $B5. This is followed by the ID of the extension. These extensions should be considered for the sequence header:

  1. Sequence Extension
  2. Sequence Display Extension
  3. Quant Matrix Extension
  4. Copyright Extension
  5. Sequence Scalable Extension

MPEG-2 Elementary Video

Sequence Extension

Extensions have the ID $B5. This is followed by the ID of the extension, here $1.

Construction

  1. 4 bytes: EXTENSION_START_CODE = $000001B5
  2. 4 bits: Start Code Identifier - Sequence Extension = $1
  3. 4 bit: profile
  4. 4 bits: levels
  5. 1 bit: progressive sequence
  6. 2-bit: chroma format
  7. 2 bit: wide extension
  8. 2 bits: height extension
  9. 12-bit: bit rate extension
  10. 1 bit: markers
  11. 8-bit: VBV Buffer Extension
  12. 1 bit: low delay
  13. 2 bits: Frame rate extension numerator
  14. 5 bits: Frame rate extension denominator

As a scheme:

  7 6 5 4 3 2 1 0
0 EXTENSION_START_CODE
 
$000001B5
1
2
3
4 Boot Code Identifier = $1 profile
5 levels program chroma width ext.
6 still BE. height ext. Bit Rate Extension
7 nor bit rate extension marker
8th VBV Buffer Extension
9 Low Delay Framerate Ext N Framerate Ext D

 
Note: In a source, four bits are used for the profile. In Andrew Duncan, the first bit of this is called 'Profile/Level Escape', with the value 0 being reserved.

Explanations

The profiles are:

value profile Typical for
1 High profile production equipment requiring 4:2:2
2 Spatially Scalable Profile simulcasting
3 SNR Scalable Profile simulcasting
4 Main profiles 95% of TVs, VCRs, cable applications
5 Simple profiles Low-cost memory, eg no B pictures

 

The profiles Multiview and 4:2:2 are sometimes also specified, but without coding.

The levels are:

value profile Typical for
4 high level HDTV production rates: e.g. 1920 x 1080 x 30 Hz
6 High 1440 levels HDTV consumer rates: e.g. 1440 x 960 x 30 Hz
8th main level CCIR 601 rates: eg 720 x 480 x 30 Hz
10 low level SIF video rate: e.g. 352 x 240 x 30 Hz

 

Allowed combinations of level and profile:

  Simple Main SNR
scalable		 Spatially
scalable		 High multiview 4:2:2
high level   X     X    
High-1440 level   X   X X    
main level X X X   X X X
low level   X X        

 

The chrominance values:

value profile description
1 4:2:0 half resolution in both dimensions (most common format)
2 4:2:2 Half resolution in horizontal direction (High Profile only)
3 4:4:4 full resolution (not allowed in any currently defined profile)

 

Low Delay means that no B-frames are used. "Frame reordering delay is not present i the VBV description, skipped pictures (VBV underflow) may occur." The Framerate Extension Numerator and Denominator are multiplied by the base framerate.

 

MPEG-2 Elementar Video

Sequence Display Extension

Extensionen are ID $B5. The ID is $2.

Aufbau

  1. 4 Byte: EXTENSION_START_CODE = $000001B5
  2. 4 Bit: Start Code Identifier - Sequence Display Extension = $2
  3. 3 Bit: Video Format
  4. 1 Bit: Color, if set:
    1. 1 Byte: Color Primaries
    2. 1 Byte: Transfer Characteristics
    3. 1 Byte: Matrix Coefficients
  5. 14 Bit: Display Width
  6. 1 Bit: Marker
  7. 14 Bit: Display Height

Als Schema:

  7 6 5 4 3 2 1 0
0 EXTENSION_START_CODE
 
$000001B5
1
2
3
4 Start Code Identifier = $2 Video Format Color
5 Color Primaries
6 Transfer Characteristics
7 Matrix Coefficients
5 / 8 Display Width
6 / 9 Display Width Marker D H
7 / 10 Display Height
8 / 11 Display Height ...

 

Explainations

Video Formats are:

Value Format
0 Component
1 PAL
2 NTSC
3 SECAM
4 MAC
5-8 Reserved

 

Color Primaries and Transfer Characteristics are:

Wert Profil
0 Forbidden
1 ITU-R Rec. 709 (1990)
2 Unspecified
3 Reserviert
4 ITU-R Rec. 624-4 System M
5 ITU-R Rec. 624-4 System B, G
6 SMPTE 170M
7 SMPTE 240M (1987)
... Reserviert

 

Matrix Coefficients:

Value Profile
0 Forbidden
1 ITU-R Rec. 709 (1990)
2 Unspecified
3 Reserved
4 FCC
5 ITU-R Rec. 624-4 System B, G
6 SMPTE 170M
7 SMPTE 240M (1987)
... Reserved

Quant Matrix Extension

Extensions have the ID $B5. The ID of this extension is $3.

Construction

  • 4 bytes: EXTENSION_START_CODE = $000001B5
  • 4 bits: Start Code Identifier - Quant Matrix Extension = $3
  • 1 bit: Load Intra Quantiser Matrix, if 1 then
    • 64 bytes: intra quantizer matrix
  • 1 Bit: Load Non Intra Quantiser Matrix, if 1 then
    • 64 bytes: non-intra quantiser matrix
  • 1 bit: Load Chroma Intra Quantiser Matrix if 1 then
    • 64 bytes: Chroma Intra Quantizer Matrix
  • 1 bit: Chroma Non Intra Quantiser Matrix, if 1 then
    • 64 bytes: Chroma Non Intra Quantizer Matrix

As a scheme:

 76543210
0EXTENSION_START_CODE
 
$000001B5
1
2
3
4Boot Code Identifier = $3Load?Intra Quantizer Matrix
5-67Intra Quantizer Matrix
68Intra Quantizer MatrixLoad?NIQM
69-131Non Intra Quantizer Matrix
132 Non Intra Quantizer MatrixLoad?CIQM
133-195Chroma Intra Quantizer Matrix
196Chroma Intra Quantizer MatrixLoad?
197-260Chroma Non Intra Quantizer Matrix

Copyright extension

Extensions have the ID $B5. This extension has the ID $4.

Construction

  • 4 bytes: EXTENSION_START_CODE = $000001B5
  • 4 bits: Start Code Identifier - Copyright Extension = $4
  • 1 bit: copyright flag
  • 8 bits: copyright identifiers
  • 1 bit: original or copy
  • 7 bits: Reserved
  • 1 bit: markers
  • 20 bit: copyright number 1
  • 1 bit: markers
  • 22 bit: copyright number 2
  • 1 bit: markers
  • 22 bit: copyright number 3

As a scheme:

 76543210
0EXTENSION_START_CODE
 
$000001B5
1
2
3
4Boot Code Identifier = $4copyright
flag		copyright identifiers
5nor copyright identifierscopy?reserved
6reservedmarkerCN 1
7nor copyright number 1
8thnor copyright number 1
9still CN 1markerCopyright number 2
10nor copyright number 2
11nor copyright number 2
12still CN 2markerCopyright number 3
13nor copyright number 3
14nor copyright number 3

Sequence Scalable Extension

Extensionen haben die ID $B5. Diese Extension hat die ID $5.

Aufbau

  • 4 Byte: EXTENSION_START_CODE = $000001B5
  • 4 Bit: Start Code Identifier - Sequence Scalable Extension = $5
  • 2 Bit: Scalable Mode (Data partioning, Spartial, SNR, Temporal)
  • 4 Bit: Layer ID

Ist der Scalable Mode "spatial scalability"

  • 14 Bit: Lower Layer Prediction Horizontal Size
  • 1 Bit: Marker
  • 14 Bit: Lower Layer Prediction Vertical Size
  • 5 Bit: Horizontal Subsampling Factor M
  • 5 Bit: Horizontal Subsampling Factor N
  • 5 Bit: Vertical Subsampling Factor M
  • 5 Bit: Vertical Subsampling Factor N

Ist der Scalable Mode "temporal scalability"

  • 1 Bit: Picture Mux Enable, wenn 1 dann
    • 1 Bit: Mux To Progressive Sequence
  • 3 Bit: Picture Mux Order
  • 3 Bit: Picture Mux Factor

Als Schema

 76543210
0EXTENSION_START_CODE
 
$000001B5
1
2
3
4Start Code Identifier = $5Scalable ModeLayer ID
5noch Layer ID 

Scalable Mode = "spatial scalability":

 76543210
5 Lower Layer Prediction Horizontal Size
6noch Lower Layer Prediction Horizontal Size
7MarkerLower Layer Prediction Vertical Size
8noch Lower Layer Prediction Vertical SizeHSF M
9noch Horizontal Subsampling Factor MHorizontal Subsampling Factor N
10n. HSF NVertical Subsampling Factor MVSF N
11noch Vertical
Subsampling Factor N		 

Scalable Mode = "temporal scalability":

 76543210
5 Picture
Mux
Enable		Mux zu
Progr.
Sequence		Picture Mux OrderPMF
6noch Picture
Mux Faktor		 

Group of Pictures

The ID $B8 follows the PACK_START_CODE_PREFIX for the GROUP_START_CODE. The length of the header is 4 bytes.

Construction

  • 4 bytes: GROUP_START_CODE = $000001B8
  • 1 bit: drop frame
  • 5 bit: Time code hours from 0 to 23.
  • 6 bit: Time code minutes from 0 to 59.
  • 1 bit: markers
  • 6 bit: Time Code seconds from 0 to 59.
  • 6 bit: Time Code Picture from 0 to 59.
  • 1 bit: Closed GOP
  • 1 bit: broken link

As a scheme

 76543210
0GROUP_START_CODE
1
2
3
4Drop
frame		Time code hoursTime code minutes
5still time code minutesmarkerTime code seconds
6still time code secondsTime Code Picture
7nor
TCP		Closed
GOP		broken
link		 

Explanations

The drop frame is used for NTSC to lower the frame rate from 30 to 29.97 fps.

The marker must again be set.

A GOP is closed if the pictures in a GOP relate only to pictures in its own GOP. Even if the stream is not encdet closed, the first and penultimate (CCE Basic) or last (TMPG Encoder) GOP are closed.

The broken link flag is set when frames refer to frames that no longer exist after a cut.

Picture Header

Dem PACK_START_CODE_PREFIX folgt der PICTURE_START_CODE mit der ID $00.

Aufbau

  • 4 Byte: PICTURE_START_CODE = $00000100
  • 10 Bit: Temporal Reference
  • 3 Bit: Coding Type
  • 16 Bit: VBV Delay.

Nur bei P- und B-Frames:

  • 1 Bit: full fel forward vector
  • 3 Bit: forward f code

Nur bei B-Frames:

  • 1 Bit: full backward vector
  • 3 Bit: backward f code

Extra Informationen:

  • 1 Bit: Extra Info Bit Set
  • 1 Byte: Extra Information, wenn Extra Bit gesetzt ist.
  • 1 Bit: Extra Info Bit cleared

Als Schema

 76543210
0PICTURE_START_CODE
1
2
3
4Temporal Reference
5Temporal ReferenceCoding TypeVBV Delay
6noch VBV Delay
7noch VBV Delayfull fel forward vectorforward f code
8noch forward f codefull backward vectorbackward f codeExtra Bit setExtra Information
9Noch Extra Information...Extra Bit cleared

Erläuterungen

Die Temporal Reference ist die Reihenfolge, in welcher die Bilder angezeigt werden sollen. Das erste Bild der Gruppe hat den Wert 0.

Die Coding Types sind:

  • Verboten
  • I - Intra Coded
  • P - Predictive Coded
  • B - Bidirectionally Predictive Coded
  • D - DC Intra Coded
  • Reserviert
  • Reserviert
  • Reserviert

Das VBV Delay wird bei konstanten Bitraten in 90 kHz Cyclen angegeben. Bei variablen Bitrate wird der Delay auf FFFF gesetzt.

Zu den forward und backward vectors sowie den Extra Informationen fehlen mir weitergehende Informationen. Die Extra Information besteht aus neun Bit. Das erste ist der Indikator dafür, ob Extra Informationen folgen. Die folgenden 8 bit stellen die Extra Information dar.

Extensionen

Bei MPEG-2 schliessen sich dem Picture Header verschiedene Extensionen an. Die ID der Extension ist $B5. Daran schliesst sich die ID der Extension an. Für den Picture Header dürften diese Extensionen in Frage kommen:

Picture Display Extension

The extension start code with the ID $B5 is followed by four bits with the extension ID $B7.

Construction

  • 4 bytes: EXTENSION_START_CODE = $000001B5
  • 4 bits: Start Code Identifier - Picture Display Extension = $7
  • For 0 = i < number_of_frame_centre_offsets (maximum 3 offsets)
    • 2 bytes (Int16): frame_centre_horizontal_offset
    • 1 bit: markers
    • 2 bytes (Int16): frame_centre_vertical_offset
    • 1 bit: markers

As a scheme

 76543210
0EXTENSION_START_CODE
 
$000001B5
1
2
3
4Boot Code Identifier = $7frame_centre_horizontal_offset
5nor frame_centre_horizontal_offset
6nor frame_centre_horizontal_offsetmarkerframe_centre_vertical_offset
7nor frame_centre_vertical_offset
8thnor frame_centre_vertical_offsetmarker...

Explanations

This extension is not necessary for the normal decoding process. However, it allows the picture to be positioned on the display. An application for this is Pan & Scan . This extension must be preceded by a sequence display extension.

frame_centre_horizontal_offset
Is the horizontal offset in units of 1/16 sample. A positive value means the center of the picture is to the right of the center of the display.

frame_centre_vertical_offset
Is the vertical offset in units of 1/16 sample. A positive value means the center of the picture is below the center of the display.

The size of the display is defined in the Sequence Display Extension. The coordinates for the decoded picture in the picture display extension. The center of the decoded picture is the center of the display. A picture can refer to one, two or three decoded fields, ie it can contain up to three offsets.

The number of offsets results from the flags progressive_sequence, repeat_first_field and top_field_first.

if ( progressive_sequence == 1)
   { if ( repeat_first_field == 1 )
        { if ( top_field_first == 1 )
             number_of_frame_centre_offsets = 3
          else
             number_of_frame_centre_offsets = 2
        }
        else
        {
        number_of_frame_centre_offsets = 1
        }
   }
   else
   { if (picture_structure == "field")
        { number_of_frame_centre_offsets = 1
        }
        else
        { if (repeat_first_field == 1 )
             number_of_frame_centre_offsets = 3
          else
             number_of_frame_centre_offsets = 2
        }
   }

Das Flag progressive_sequence ist in der Sequence Extension enthalten. repeat_first_field, top_field_first und picture_structure in der Picture Coding Extension.

Das Fehlen der Offsets bedeutet, dass die zuvor verwendeten Werte verwendet werden sollen. Das gilt auch, wenn nicht alle Offsets angegeben sind. Nach einem Sequence Header werden wieder Nullwerte verwendet, bis wieder Werte angegeben werden.

Das Bild unten stammt aus einem Draft zur ISO 13818-2.

Picture Coding Extension

The extension start code with the ID $B5 is followed by four bits with the extension ID $B8.

Construction

  • 4 bytes: EXTENSION_START_CODE = $000001B5
  • 4 bits: Start Code Identifier - Picture Coding Extension = $8
  • 4 bits: f_code[0][0] - forward horizontal
  • 4 bits: f_code[0][1] - forward vertical
  • 4 bits: f_code[1][0] - backward horizontal
  • 4 bits: f_code[1][1] - backward vertical
  • 2-bit: Intra DC precision
  • 2-bit: Picture Structure
  • 1 bit: top field first
  • 1 bit: Frame Pred Frame DCT
  • 1 bit: Concealment Motion Vectors
  • 1 bit: Q scale type
  • 1 bit: Intra VLC format
  • 1 bit: alternate scan
  • 1 bit: Repeat First Field
  • 1 bit: Chroma 420 type
  • 1 bit: progressive frame
  • 1 bit: Composite Display Flag, if set:
    • 1 bit: V axis
    • 3 bits: field sequence
    • 1 bit: Subcarrier
    • 7 bits: burst amplitude
    • 8 bits: sub-carrier phase

As a scheme

 76543210
0EXTENSION_START_CODE
 
$000001B5
1
2
3
4Boot Code Identifier = $8f_code[0][0]
5f_code[0][1]f_code[1][0]
6f_code[1][1]Intra DC Prec.Picture Structure
7TFFFPF
DCT		CMVQ scale typeIntra VLC formatAlternate ScanRepeat First FieldChroma 420 type
8thProgressive framescomposite display?V axisField Sequencesubcarriersburst amplitude
9still BAsub-carrier phase
10nor SCP 

Explanations

f_code[s][t]
The values ​​are used to decode the motion vectors. The value 0 is forbidden, 1 to 9 and 15 are allowed.

Intra DC Precision
Accuracy with which the discrete cosine transformation is used. The Intra DC Mult(iplikator) is derived from this.

valueaccuracymultiplier
008 bits8th
019 bits4
1010 bits2
1111 bits1

Picture Struktur

WertPicture Struktur
00Reserviert
01Top Field - oberes Halbbild
10Bottom Field - unteres Halbbild
11Frame Picture - Vollbild

Wenn ein Frame in Halbbildern encodet wurde, muss immer ein Paar mit gleichem Picture Coding Type vorliegen.

Top Field First
Dieses Flag ist von Picture Structure, Progressive Sequence und Repeat First Field abhängig.
Bei nicht gesetzten Flag Progressive Sequence dient es beim Decoding der Rekonstruktion des Frames und gibt an, ob das First Field (oberes Halbbild) zuerst ausgegeben wird.
Bei gesetzten Flag Progressive Sequence, gibt es in Verbindung mit dem Flag Repeat First Field an, wie oft ein Frame beim Decoding ausgegeben wird. Dies bedeutet, bei Repeat First Field = 0 und Top Field First = 0 wird ein progressives Frame, bei Repeat First Field = 1 und Top Field First = 0 werden zwei identische progressive Frames und bei Repeat First Field = 1 und Top Field First = 1 drei identische progressive Frames ausgegeben.

Frame Pred Frame DCT
Wenn dieses Flag gesetzt ist, wird nur Frame DCT und Frame Prediction genutzt. Bei Field Picture (Halbbildern) ist es 0, bei progressiven Frames 1.

Concealment Motion Vectors
Dieses Flag gibt an, ob die Intra Macroblocks mit Motion Vectors encoded wurden.

Q Scale Type
Diesses Flag wird für den Quantiser Scale Factor verwendet.

Intra VLC Format
Dieses Flag wird für die Bestimmung der DCT Koeffizienten verwendet.

Alternate Scan
Dieses Flag wird für die Bestimmung der DCT Koeffizienten verwendet.

Repeat First Field
Wenn die Flags progressisve_sequence (siehe Sequence Extension Header) und progressive_frame nicht gesetzt sind, ist das Flag repeat_first_field ebenfalls nicht gesetzt. Beim Decoden wird dann das Frame aus zwei Feldern zusammengesetzt. Ist das Flag progressive_sequence nicht aber das Flag progressive_frame gesetzt, wird das Frame aus zwei Feldern zusammengesetzt. Das erste Feld (Top Field oder Bottom Field) wird durch das Flag top_field_first identifiziert und wird von dem anderen gefolgt. Ist dann das Flag repeat_first_field gesetzt, wird das Frame aus drei Fields zusammengesetzt. Das erste Field wird durch das Flag top_field_first bestimmt und von dem anderen gefolgt. Anschließend wird das erste Field wiederholt. Ist das Flag progressive_sequence gesetzt und das Flag repeat_first_field nicht, wird das Frame aus einem Frame decodiert.

Chroma 420 Type
Ist genauso gesetzt wie Progressive Frame. Existiert aus historischen Gründen.

Progressive Frame
Ist das Flag nicht gesetzt, bedeutet dies, dass die beiden Fields eines Frame zwei interlaced Fields sind. Repeat First Field muss 0 sein (two field duration). Ist das Flag gesetzt, bedeutet dies, dass die beiden Fields zu einem verschmolzen sind. Picture Structure muss auf "Frame" und Frame Pred Frame DCT auf 1 gesetzt sein.

Composite Display Flag
Dieses Flag ist gesetzt, wenn die Picture, aus denen das MPEG encodet wurde, als (analoges) Composite Video encodet waren. Die Informationen beziehen sich auf die Exstension folgenden Picture. Handelt es sich um ein Frame Picture, beziehen sich die Informationen auf das First Field. Die Informationen werden für das Second Field angepasst, da diese nicht gespeichert werden können. Die folgenden Elemente werden für das Decoding nicht genutzt. Das Repeat First Field Flag und das Composite Display Flag dürfen nicht gleichzeitig gesetzt sein.

V Axis
1-bit integer used only when the bitstream represents a signal that had previously been encoded according to PAL systems. v_axis is set to 1 on a positive sign, v_axis is set to 0 otherwise.

Field Sequence
Gibt die Nummer des Feldes einer acht Field Sequence bei einem PAL System oder einer fünf Field Sequence bei einem NTSC System entsprechend nachfolgender Tabelle an:

Field SequenceFrameField
00011
00112
01023
01124
10035
10136
11047
11148

Sub Carrier
Ist das Flag nicht gesetzt ist das sub-carrier/line frequency relationship korrekt.

Burst Amplitude
gibt die Burstamplitude für PAL und NTSC an.

Sub Carrier Phase
Gibt die Phase des Referenz Sub Carrier der Fieldsynchronisation an.

Sub Carrier PhasePhase
0([360° / 256] * 0)
1([360° / 256] * 1)
......
255([360° / 256] * 255)

mpeg2/mpeg2_elementary_stream_structure.1652205282.txt.gz · Last modified: 2022/05/10 17:54 by emcodem