What is implicit for all QC Items
The following general rules should be kept in mind when looking at the Input and Output Parameters of the QC Items, unless specified differently for specific Parameters.
The system shall report deviation from the defined thresholds/tolerances
Note that the thresholds/tolerances may include user-defined expected, required or allowed values. These are defined as singular parameters, but it is implicit that lists of expected values may be used too. Example: an aspect ratio QC Item may have a user-defined expected value list of 4:3 and 14:9. The system shall report when the aspect ratio is 16:9.
The system shall report the relevant location(s) for each result.
The preferred way to report the time location of an event is with the timing extension of the EBU QC data model (TimingExtensionMediaPlaybackEditUnits, Annex D of the data model). The QC report best practice guidance asks for it to be present in every QC Report.
With the extension:
- A report states one edit rate, the number of divisions per second, for example
25/1,24000/1001or1000/1. - The
StartandEndof a location are whole numbers (0 or more) of those divisions, counted on the playback timeline of the media that is tested. 0 is the start of playback. This is not the same as timecode, and it does not depend on the start timecode of the container or bitstream. Endis not beforeStart. The same value for both is an instant, with no duration. When one of them is left out, the segment is open on that side.
Example: at an edit rate of 25/1, a Start of 250 and an End of 375 describe the segment from 10 s to 15 s after the start of playback, which is 5 s long.
Choose an edit rate that is accurate enough for what is reported. Audio events may need a finer rate than the video frame rate, for example 1000/1 (milliseconds). Timecode or frame counts may still be shown as extra references for people reading a report.
The Inputs and Outputs of an Item say whether they refer to a position in time or in the picture; this rule says how a time position is expressed.
The system should report changes in measured values.
If the system will not report changes, this should be made clear to the user. Example: a system reports the aspect ratio is 4:3 from 10:00:02:00 to 10:02:02:00 and 16:9 from 10:02:02:00 to 10:03:00:00.
Service references
Multichannel audio services (programmes) that are embedded in a single track should reference the audio channels as mapped in the bitstream. For multichannel audio services (programmes) that are a collection of tracks (i.e., an EBU R123 map of AES channels or a Dolby E program in an AES stream), the audio channels should be referenced by the externally defined map for these tracks (i.e., EBU R 123 or the Dolby E program). For audio and/or video services in programme/transport streams, PIDs should be used for unique stream identification.
References
References in the v1.0 (and higher) versions of the QC Items refer to the latest version of a specification, unless they are explicitly dated. E.g. SMPTE ST 377-1:2009
References are picked from the managed reference list where possible, so that spelling, links and editions are the same in every Item.
Types of specs to reference
We are using a practical approach to referencing specs; which means we do not only reference formal standards, but also industry specs where relevant (e.g. Dolby-E specifics). This also is relevant in the video codecs domain (e.g. XDCAM, IMX, RDD-9, ...). The criterion is that the spec should be published.
Supported wrapper formats
Some QC Items are focussed on MXF, but can be relevant for other wrapper formats too. Due to resource constraints we do not include detail on the other wrappers (at least for now). Example: Quicktime.
Note that MXF-only Items are signalled using an ‘MXF’ logo in the QC Item card’s image and the 'MXF-only' tag.
Readout, measurement and calculated values
Each QC Item states its Analysis method:
- readout: the result is a value written in the file, or a simple inference from such values (for example duration = number of frames / frame rate);
- measurement: the result comes from analysing the decoded audio or video (for example loudness);
- readout and measurement: both are needed, which is typical for crosschecks.
Leave it empty only when it is not known, or when the Item deliberately does not prescribe how to implement the test.
If a test must report a value read from the file and a value derived from it side by side, define them as two separate outputs, for example DurationWrapper and DurationCalculated, and say in the description how the second one is derived.
The Analysis method is part of the EBU QC data model 2026-04 and is only published in API v3; see also Editing QC Items.
Implicit inputs and outputs
Some Inputs and Outputs are needed by every test, so they are not described in each Item. A system is required to manage them.
- Content: the file or stream that is analysed, in the input, and the reference to it in the output report.
- Scope: any limit to specific time intervals or areas of the picture.
- Tracks and wrapper location: the tracks the test applies to and, for tests on the wrapper, where in the wrapper the result was found.
Do not add Inputs or Outputs for these. Where an Item's own value refers to a position, a track or a wrapper location, use the positioning flags on that Input or Output. See also Editor guidelines.
Checks on specific channels
We do not preclude systems to offer users the option to limit checks to certain channels. E.g. perform a silence check only on audio track 1 instead of on all channels. To limit the amount of generic text, we do not repeat this option for each QC Item, but regard it to be implicit, where relevant.
When tests cannot be done...
If information is not available, e.g. audio bit depth is not defined in the wrapper format used by a particular file, than an Item (and any related x-check) does not apply. For some QC Items we do not define wrapper tests, as we know the information typically is not available at the wrapper level.
Programme vs. non-programme content testing
System shall be able to apply test criteria between specified timecodes, e.g. from the start to the end of a programme, allowing line-up and non-relevant content (such as clean backgrounds for international markets) to be excluded.