Subtitling videos can be something really challenging for a translator. Text length will be very often a limitation editors will need to keep in mind so
Prepare your text extraction profile
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You can even combine this rule with the Global Setting in the Translation Editor to prevent users from keep typing text, so that it is impossible to enter any additional character in the segment.
Work in a suited environment
It would be almost impossible to validate a subtitle without having it previously played in their final context. Subtitles are ment meant to be and additional layer in a video and Wordbee makes it possible to review them directly in the video module for subtitle preview.