Performing quality control is essential in order to ensure that the Dolby Vision metadata is valid and correctly mapping. Therefore, the Dolby Vision Metadata should be checked for quality and integrity before leaving the color suite.
 

In this article we will discuss the following topics:
 

• Metadata validation
• Preliminary checks
• Comprehensive visual QC
• Recommended infrastructure

 


 

Metadata validation

Dolby Vision metadata can be delivered either as an XML sidecar metadata file or embedded in the video MXF (mezzanine file) of a Dolby Vision IMF package. Verifying such metadata can be done using the Metafier command that is part of the Dolby Vision Professional Tools. Metafier supports extracting, upgrading, checking and validating metadata and displaying information.

 

Example validation of a DV mezzanine file:

./metafier --validate <file.mxf>

 

Validation Examples:

Metafier generates a validation report which is a summary of the information that is stored in the XML. It also checks the XML for possible errors and entries or values that may result in errors during mapping.
 

Validation report example for XML v2.0.5

$ ./metafier --validate <file.xml>
12/16/2020/18:09:24.329581847 Metadata: Validation Summary:
=========================
Metadata version: "2.0.5"
Level254 CMVersion: 2 1
Aspect Ratios (Canvas - Image): 1.77778 - 2.39
Frame Rate: 24fps
Mastering Monitor: 1000-nit, P3, D65, ST.2084, Full (ID 20): Bit Depth: 16bit - Diagonal: 42.00in - Application Type: ALL - Color Info: "pq(0.0001,1000) rgb computer p3d65"
Mastering Monitor Validation Test: PASS
Target Displays Validation Test: PASS
Level6 (MaxFALL - MaxCLL): 0.00 - 0.00
Color Encoding: "u16 444 pq(0,10000) rgb computer p3d65"
Color Encoding Validation Test: PASS
Overlapping Shots Validation Test: PASS
Gap between Shots Validation Test: PASS
Negative Shot duration Validation Test: PASS
Per-Frame Data out-of-range Validation Test: PASS
Number of Shots: 21
Frame Range: 180000-184043
L2 Trim Count (TargetID, count): (1, 205) (27, 201)
L1 Metadata Validation Test: PASS
L2 Metadata Validation Test: PASS
=========================
12/16/2020/18:09:24.330120863 metafier: No issues found in the Metadata

 

Validation report example for XML v4.0.2

$ ./metafier --validate <file.xml>
12/16/2020/18:08:14.822607414 Metadata: Validation Summary:
=========================
Metadata version: "4.0.2"
Level254 CMVersion: 4 1
Aspect Ratios (Canvas - Image): 1.77778 - 2.39
Frame Rate: 24fps
Mastering Monitor: 1000-nit, P3, D65, ST.2084, Full (ID 20): Bit Depth: 16bit - Diagonal: 42.00in - Application Type: ALL - Color Info: "pq(0.0001,1000) rgb computer p3d65"
Mastering Monitor Validation Test: PASS
Target Displays Validation Test: PASS
Level6 (MaxFALL - MaxCLL): 0.00 - 0.00
Color Encoding: "pq(0,10000) rgb computer p3d65"
Color Encoding Validation Test: PASS
Overlapping Shots Validation Test: PASS
Gap between Shots Validation Test: PASS
Negative Shot duration Validation Test: PASS
Per-Frame Data out-of-range Validation Test: PASS
Number of Shots: 21
Frame Range: 0-4043
L2 Trim Count (TargetID, count): (1, 485) (27, 485) (48, 485)
L8 Trim Count (TargetID, count): (1, 271) (27, 148)
L1 Metadata Validation Test: PASS
L2 Metadata Validation Test: PASS
L3 Metadata Validation Test: PASS
L8 Metadata Validation Test: PASS
L9 Metadata Validation Test: PASS
=========================
12/16/2020/18:08:14.822726058 metafier: No issues found in the Metadata

 

Validation report example for XML v5.1.0

$ ./metafier --validate <file.xml>
04/19/2021/21:24:31.888790847 Metadata: Validation Summary:
=========================
Metadata version: "5.1.0"
Level254 CMVersion: 4 1
Aspect Ratios (Canvas - Image): 1.77778 - 1.77778
Frame Rate: 24fps
Mastering Monitor: 1000-nit, P3, D65, ST.2084, Full (ID 20): Bit Depth: 16bit - Diagonal: 42.00in - Application Type: ALL - Color Info: "pq(0.0001,1000) rgb computer p3d65"
Mastering Monitor Validation Test: PASS
Target Displays Validation Test: PASS
Level6 (MaxFALL - MaxCLL): 0.00 - 0.00
Level11 (ContentType - IntendedWhitePoint): 0 - 0
Color Encoding: "pq(0,10000) rgb computer p3d65"
Color Encoding Validation Test: PASS
Overlapping Shots Validation Test: PASS
Gap between Shots Validation Test: PASS
Negative Shot duration Validation Test: PASS
Per-Frame Data out-of-range Validation Test: PASS
Number of Shots: 4
Frame Range: 0-58
L2 Trim Count (TargetID, count): (1, 4) (27, 4) (48, 4)
L8 Trim Count (TargetID, count): (1, 4) (18, 4)
L1 Metadata Validation Test: PASS
L2 Metadata Validation Test: PASS
L3 Metadata Validation Test: PASS
L8 Metadata Validation Test: PASS
L9 Metadata Validation Test: PASS
L11 Metadata Validation Test: PASS
=========================
04/19/2021/21:26:24.459675319 metafier: INFO No issues found in the Metadata
 

Metadata validation checks

Checks that will trigger an ERROR:

• CM algorithm version values other than:
  • CMv2.9 valid versions are: (0 0), (2 0), (2 1), (2 2), (2 4)
  • CMv4.0 valid versions are currently: (4 0), (4 1), (4 2)
• Mastering display metadata are within valid ranges
• Target display metadata are within valid ranges
• Multiple target displays with the same peak brightness value
• Predefined Mastering and Target displays are checked against the display database for matching:
  • Color Primaries
  • White Point
  • Encoding
• Color Encoding metadata are valid
• Shots do not overlap
• Shots do not have gaps
• No shots contain negative duration
• Per-frame offsets are within shot boundaries
• L1 metadata values are within 0.0 to 1.0
• Only one set of L1 values per shot
• L2 and L8 target IDs have corresponding target displays recorded in L0
• L2 and L8 metadata values are within -1.0 to 1.0
• L3 metadata values are within -1.0 to 1.0
• L9 metadata values are within -1.0 to 1.0
• L11 metadata values are within the defined set of index values
• No duplicate trims in the same shot for the same target display ID

 

Checks that trigger a WARNING:

• Custom mastering displays containing non-standard color primaries
• Predefined mastering and target displays that contain different values for peak and min brightness values
• L1 values equal 0,0,0 for a duration longer than 1 second
• L1 values are the same for more than 15 consecutive shots
• L2 or L8 values are the same for more than 15 consecutive shots
• Shots that contain an HDR trim without a 100-nit trim
• Shots that contain no trims
• Shots that contain trims with a lift value greater than +0.025 when the aspect ratio is letterboxed when using the --with-lift option in conjunction with --validate

Additional checks in mezzinator and cm_offline:

• Checks the canvas aspect ratio metadata against the image canvas during processing
• Checks if the total duration in XML matches the image sequence total duration
• Checks that the XML start frame starts with zero with MXF and ProRes image sequences

 


 

Preliminary checks

To eliminate potential errors before performing a more comprehensive visual QC, one could run the following preliminary checks:

Check duration, frame numbering, frame rate

The duration of the content as specified in the metadata (XML) must match the number of frames that were rendered out of the color corrector. If there is a mismatch, it must be corrected.
The frame rate listed inside the Dolby Vision metadata must match to the corresponding video content.
 

Image specifications and information

The specifications of the rendered image sequence must conform to that requested by the client or entity that commissions the project. Ensure that all technical and tag data match your delivery requirements. This must be confirmed before sending the content for QC or any further processing.
A great tool to check technical and tag data of video and audio files is MediaInfo that's available via the Apple App Store or directly from the MediaInfo website
 

Color Encoding

The color encoding fields in the metadata must match the specifications and format of the rendered image sequence. These include the color primaries, white point and signal range (video/legal/full/data).
See the Color Primaries inside a Dolby Vision XML for further info.
 

Mastering Display

The mastering display as specified in the metadata is a parameter that is critical to all the downstream processing for which the metadata is used. It is therefore important to ensure that the right mastering display is specified in the metadata.
 

Canvas and Image Aspect Ratio

Ensure that the canvas aspect ratio is set to the full resolution of a frame. For UHD (3840x2160) and HD (1920x1080) deliveries this should always be 1,177778. The image aspect ratio must be set to reflect the active image within the full resolution of the frame. If one or both of these settings are not set correctly, tone mapping will not be applied correctly to the image.

 

Trim metadata

Trim metadata, if present must also pass Metafier validation. Validating letterboxed content for positive lift values above 0.025 we recommend using the following command:

./metafier --validate --with-lift <file.mxf>

 
 

Comprehensive visual QC

A comprehensive quality control confirms that there are no image rendering errors present and that the image and associated metadata are in sync to avoid any tone mapping/timing errors.
Check the Dolby Vision Master (16-bit TIFF/ProRes 4444XQ) and its corresponding XML file or the Dolby Vision mezzanine deliverable reviewing a mapped version (such as Rec.709/100 nits) using the content mapping functionality and check the visual result.
You can either select to review a mapped version using the content mapping functionality of a partner solution (iCMU or eCMU) or you can use the tool CM_offline (part of the Dolby Vision Professional Tools) to render a stand-alone tone mapped version and visually check the result.


Learn how to review a Dolby Vision Master or a Dolby Vision IMF in our tutorial .




Any visual errors can be traced back to either the image master or the metadata and must be corrected before delivery to the client.

 

Recommended infrastructure

In order to perform a comprehensive quality control, QC should have access to:

• Linux/Mac/Windows workstation with the latest version of the Dolby Vision Professional Tools installed
• Dolby Vision capable playback system that supports
  • import of Dolby Vision metadata from a Dolby Vision XML
  • import of a Dolby Vision IMF
  • tone mapping by either iCMU or eCMU
    • more info on systems supporting Dolby Vision: Dolby Vision compatible Color Grading & Packaging Systems
• professional HDR reference display
• professional SDR reference display
  • more info about monitors: HDR Display Considerations
• (optional) Calibrated Dolby Vision TV set using HDMI Tunneling - Best Practises: Preview a Grade on a Dolby Vision TV using HDMI Tunneling
• HDR and SDR scopes