Identify three boundaries
An owned video has a stored raster, an active picture within it and a destination display area. Black space can belong to the stored image or be added during presentation. Cropping the file only addresses the first case and can remove real picture area if those boundaries are confused.
Inspect the media itself through a reliable production tool and compare the destination's presentation. Keep the source unchanged. A screenshot of a player inside a webpage can include several surrounding layers that are not encoded video.
Review more than one shot. Titles, credits or subtitles can extend into areas that appear empty during an ordinary scene. A crop selected from a single frame can remove those later.
Make the editorial decision explicit
If borders are stored in the source and a crop is justified, record the active region and desired output aspect. Decide whether the destination should add padding, scale the cropped image or accept another canvas. None of those choices is implied by removing black pixels.
For a hypothetical lecture, a lower caption sits partly in the stored bottom border. Cropping all visible black would damage the text. The production may need a different caption version or to preserve the border rather than pretending the crop is purely technical.
Review beginning, middle, end and any graphics-heavy sections of the derivative. Confirm the aspect and edge content in the intended destination. Retain the crop note and source so a later delivery can choose another presentation without beginning from already discarded image area.
Questions answered
Can every black bar be removed by cropping the file?
No. Some black space is added by the presentation layout.
Is a crop safe after checking one ordinary scene?
No. Review titles, credits, captions and other edge content across the programme.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.