Subtitle editor with an audio waveform and timing checks

Nothing — the editor raises a notice with a "Fix it" button by itself. Most Cyrillic subtitles are stored in windows-1251 rather than UTF-8, and that is decided from the bytes of the file, not from its extension. If the detection guessed wrong, pick the encoding by hand in the same notice: the cue list is re-read immediately, so you see the result before saving anything. "привет" is a separate case — text that was already re-encoded wrongly once — and the Fix button unwinds it.

Characters per second — the speed at which a viewer has to read. The threshold comes from the standard you pick: 17 for Netflix, 13 for children's content, 21 for the web; for character-based scripts it is lower and is applied automatically from the text of the file. Amber means over the limit, red means over it by more than a quarter. This is the one subtitle fault you cannot see in a text editor and the viewer sees instantly.

The waveform is read straight out of MP4 and MOV containers, in slices from disk, so a three-hour recording costs almost no memory. There is no such path for WebM, MKV, AVI and some audio formats, and we deliberately do not pull a thirty-megabyte video engine onto the page just for a picture. Everything else still works: the cue blocks, the ruler, the playhead and edge dragging do not depend on the waveform.

That means the file was timed at a different frame rate — usually 23.976 against 25. A constant shift cannot fix it, because the error grows toward the end. Open "Match two points", find the first cue and the last one, enter where each sits now and where it belongs, and everything between is recalculated in proportion. If the error is the same from beginning to end, an ordinary shift is enough.

Italic, bold and underline carry across every format that understands them. ASS styles, positioning and effects survive a save back to ASS or SSA; converting to SRT or VTT loses them, which is a limit of those formats, and the editor names exactly what will not fit before you download.

The converter changes the format and the encoding and repairs obvious damage without showing you the content line by line. The editor is about the content: this cue, this edge on the waveform, this typo. They share the same format engine, so you can save from here into the same sixteen formats. If all you need is "srt to vtt", the converter is quicker; if you need to fix three cues and check the reading speed, this is the place.