Merge SRT and VTT subtitle files

When you need to merge

A long recording is often cut into pieces: a webinar saved as three files, an interview with a break in the middle, a video edited in two exports. Each piece has its own subtitle file that starts at 00:00:00, so putting the files one after another gives a list in which every part begins at the top of the video. Merging fixes the times so the whole thing plays against the full video.

Part 1 ends at 00:00:09,000        Part 2 starts at 00:00:00,500

merged:
00:00:01,000 --> 00:00:03,000      Part one starts here.
00:00:04,000 --> 00:00:09,000      It runs for about ten seconds.
00:00:09,500 --> 00:00:11,500      Part two begins at its own zero.

Part 2 here was moved by the length of part 1, so its first cue, which began 0.5 seconds into its own file, now begins 0.5 seconds after part 1 ended.

Automatic and manual offsets

Leave the offset box empty and the part follows the previous one: the new offset is the end of the last cue so far plus the gap you set. That is exactly right only if each video part begins immediately after the previous part ends. If the video parts have a title card, a fade or a pause between them, the subtitle file does not know about it, so enter the real offset yourself (the length of everything before, in seconds or as 1:30) and the cues will land where the speech is. The summary under the result shows where each part starts and ends so you can check the joins.

Order, overlaps and numbering

Cues are renumbered from 1 in the result. Parts are joined in the order of the boxes. If you tick the sort option, every cue is placed in start order afterwards, which is the right choice when the parts overlap or you added them out of order, and the wrong one if you have two speakers' cues intentionally interleaved by the order of the files. After merging, the subtitle checker reports any overlap that remains.

Formats

SRT and WebVTT are both read, and you can mix them. The output is whichever format you pick. If the first part is a VTT file with cue settings (for example positioning), they are kept when the output is VTT and dropped for SRT, because SRT has nowhere to put them. See SRT to VTT if you only need to change format.

When the files do not line up

Merging assumes each part's own timing is correct. If a whole file is early or late, correct it first with the time shifter, then merge. If a file drifts (right at the start, wrong by the end) that is a different problem, and the shifter's two-point sync is the tool for it.