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0046W - GOP Length - Structure
published
0046W v2.0
Item image
GOP STRUCTURE
GOP length, distance
SMPTE ST 381-2, ...
Expected GOP Structure
GOP Structure, Mismatch
https://qc.ebu.io/items/0046W/versions/2-0-0/
Check
Report
Summary
EBU QC Id
0046W
Name
GOP Length - Structure
Status
published
Category
absolute
Lead editor
Jerome MARTINEZ
Aliases
GOP structure Maximum GOP size Maximum B picture count
Tags
video MXF
Versions
Version Status Edition date Saved by Note
Details
Description
The GOP length (GOP size) specifies the maximum distance between two full images (I-frames) i.e. the count of frames between two I-frames plus one.
A value of 0 or the absence of this property indicates either there is no limit to the GOP length or that its maximum is unknown.
The GOP length is called "N" in the representation of GOP structure frame layout .

The "Maximum B pictures count" is the number of B frames between two anchor frames (I or P).
Maximum B picture count plus 1 is called "M" in the representation of GOP structure frame layout and is the distance between two anchor frames (I or P) .

The GOP structure layout is provided by the M,N couple of integer numbers.
Definition
Used in Checks, the system shall read out the GOP length and the maximum number of B frames in the GOP which are indicated in the wrapper metadata and check if they match the expected ones specified in input. Additionally the system shall report the values and calculate the IBP frame layout of the GOP and report it.

Used in Reports, the system shall read out the values indicated in the wrapper metadata and report them. Additionally it shall calculate the IBP frame layout of the GOP and report it.
References

  • SMPTE ST 381-1

    Remark: Mapping MPEG Streams into the MXF Generic Container

  • SMPTE ST 381-2

    Remark: Mapping MPEG Streams into the MXF Constrained Generic Container

  • SMPTE ST 381-3

    Remark: Mapping AVC Streams into the MXF Generic Container

Examples

  • Input: "GOP Structure Length Expected" = 12
    Input: "GOP Structure B Frames Expected" = 2
    Output: "Check Result" = false
    Output: "GOP Structure Layout" = 2,15

    Remark: Used as a Check

  • Input: -
    Output: "GOP Structure Length" = 12
    Output: "GOP Structure B Frame" = 2
    Output: "GOP Structure Layout" = 3,12

    Remark: Used as a Report

Input parameters
Name Default value Description Data model name Unit Locator
Output parameters
Name Alias Description Data model name Unit Locator
Test material
Title Version Download
Remarks
Remarks
In MXF, GOP describing parameters are always global for all included GOPs and define the maximum value which occurs.

This Test is a combination of different readouts enhanced by the typical GOP presentation with M and N.

M stands for the distance between the anchor frames ( I or P-frames) incremented by one, N stands for the length of the GOP (from I to I-frame).

Example: for IBBPBBPBBPBBI we have M=3, N=12.

SMPTE UL for "maximum gop size" = 060e2b34.01010105.04010602.01080000
SMPTE UL for "avc maximum gop size" = 060e2b34.0101010e.04010606.01080000
SMPTE UL for "Maximum B Picture Count" = 060e2b34.01010105.04010602.01090000
SMPTE UL for "AVCMaximumBPictureCount" = 060e2b34.0101010e.04010606.01090000

Because of the possible combination of parameters, every input and output parameter is optional.
User discussions
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