The SRT subtitle format, explained

Structure

1
00:00:01,000 --> 00:00:03,500
Hello and welcome.

2
00:00:04,000 --> 00:00:06,200
<i>Two lines
are fine.</i>

1. A cue number (1, 2, 3…)
2. Start --> end, as HH:MM:SS,mmm (comma before milliseconds)
3. One or more lines of text
4. A blank line

Tags and encoding

• Widely supported: <i>, <b>, <u>; <font color> is supported by some players.
• No official encoding: UTF-8 is the modern default, but some TVs expect the local Windows code page (see encoding).

Common errors

• Dot instead of comma in times (00:00:01.000) – that's VTT style.
• Missing blank line between cues.
• End time before start time, or overlapping cues.
• Numbering gaps or duplicates (most players don't care, some do).
• Stray BOM or UTF-16 encoding on devices that don't expect it.

Opening and re-saving in Cuemend normalises all of these; overlaps and min/max durations can be fixed in clean-up.