Fixing a bug with byte order marks

Recently I’ve been tidying up the subtitles in my local media library. There are two popular file formats for subtitles: SRT (SubRip Subtitle) and WebVTT (Web Video Text Tracks). I’ve been standardising on WebVTT because it works with the HTML5 <video> element, and I play all my videos through the <video> element embedded in static websites. However, lots of subtitles are only available as SRT, so I wrote a Python function to convert SRT files to WebVTT. The formats looked simple and the conversion seemed straightforward. Famous last words! When I spot checked the converted subtitles, I noticed a bug in my handling of byte order marks (BOM), and it took several steps to fix. Failing to look for the UTF‑8 BOM A byte order mark is a special use of the zero width no-break space character U+FEFF at the beginning of a text file, which tella a program reading the file about how the text is encoded. It depends on the exact sequence of bytes used to encode the character. Here are a few…