What SBV is and where it comes from
SBV is YouTube's subtitle format: downloading "subtitle files" from YouTube often gets you a .sbv. Its structure is simpler than SRT — start and end times sit on one line separated by commas, the text follows directly underneath, and there are no cue numbers.
Why players reject it
Outside YouTube itself, most editing software and players do not support SBV. It lacks the numbering block and writes its timing line differently from SRT, so renaming the extension does nothing — the structure has to be rebuilt for real.
How to convert
Open the converter, drop in the SBV, choose SRT - SubRip as the output, then convert and download. Cue numbers are assigned fresh, and the original line breaks inside a cue are merged into one line (SRT allows multi-line cues; SBV is exported single-line here).