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0247B - Captions/Subtitles displayed early or late
published
0247B v1.0
Item image
CAPTIONS/SUBTITLES SHIFT
Audio <> Captions/Subtitles
Captions/Subtitles
Timing is in Sync
Async Captions/Subtitles
https://qc.ebu.io/items/0247B/versions/1-0-0/
Check
Report
Summary
EBU QC Id
0247B
Name
Captions/Subtitles displayed early or late
Status
published
Category
subjective
Lead editor
Matt Simpson
Aliases
closed captions hard of hearing subtitles translation subtitles
Tags
audio access service text
Versions
Version Status Edition date Saved by Note
Details
Definition
Used as a Check, the system shall detect captions/subtitles which are shifted more than N seconds before or after the location where the corresponding dialogue is spoken in the audio. Can also detect a frame rate mismatch/drift without the need to know the framerate of the audio or captions/subtitles.

Used as a Report, the system shall report the time intervals of captions/subtitles which are shifted more than N seconds before or after the location where the corresponding dialogue is spoken in the audio.
References
Examples

  • Input:
    "ServiceChannelAllocation" = 4a 1,2
    "CaptionsReference" = "foo.xml"
    "OutOfSyncCaptionTotalDurationThreshold" = 1 second
    "OutOfSyncCaptionShiftToleranceBefore" = 1 second
    "OutOfSyncCaptionShiftToleranceAfter" = 1 second

    Output:
    "CheckResult" = false
    "OutOfSyncCaptionSegment" from 00:00:00:00 to 00:30:00:00
    --> "OutOfSyncCaptionShiftAmount" = -10.0 seconds

    Remark: Used as a Check. Scenario: A 10-second test slate / identification added to the beginning of the media has caused all captions/subtitles to be displayed 10 seconds too early.

  • Input:
    "ServiceChannelAllocation" = 4a 1,2
    "CaptionReference" = foo.xml
    "OutOfSyncCaptionTotalDurationThreshold" = 60 seconds
    "OutOfSyncCaptionShiftToleranceAfter" = 5 seconds

    Output:
    "CheckResult" = false
    "OutOfSyncCaptionSegment" from 00:00:08:16 to 00:09:14:22
    "OutOfSyncCaptionSegment" from 00:00:13:00 to 00:00:16:12

    Remark: Used as a Check. Scenario: A live-captioned file is checked and shows many captions are delayed from the spoken word by more than 5 seconds.

  • Input:
    "ServiceChannelAllocation" = 4a 1,2
    "CaptionReference" = foo.xml
    "OutOfSyncCaptionTotalDurationThreshold" = 60 seconds
    "OutOfSyncCaptionShiftToleranceBefore" = 1 second
    "OutOfSyncCaptionShiftToleranceAfter" = 5 seconds

    Output:
    "CheckResult" = false
    "OutOfSyncCaptionSegment" from 00:00:08:16 to 00:09:14:22
    "OutOfSyncCaptionSegment" from 00:00:13:00 to 00:00:16:12

    Remark: A programme is distributed with SCC hard of hearing subtitles which utilize a frame rate of NTSC-30 (29.97 fps). However, the media frame rate is actually PAL-25. In this scenario, the hard of hearing subtitles displayed on screen will consistently drift farther from the spoken word at a rate of 10 seconds per minute. In other words, 5 minutes into the programme, the subtitles are delayed by nearly a full minute (50 seconds)

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
This kind of issue is most often seen when "live-captioned" material is re-purposed for the web, etc. Live-captioned content is typically delayed between 7 and 12 seconds behind the spoken word.

Another example of this issue is where the entire subtitle is consistently shifted by a fixed amount. This could be the result of an edit which has caused the media to contain extra content not accounted for in the timing of the closed captions. For example, a 10-second test slate / identification added to the beginning of the media would cause all subtitles to be displayed 10 seconds too early.
User discussions
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