SRT to ASS

Advanced SubStation Alpha grew out of SubStation Alpha, a 1990s Windows editor, and became the format of anime fansubs and of Aegisub, the editor most typesetters use. Its strength is that style lives in the file. Where SRT says only when and what, ASS also says how: font, size, colors, outline width, shadow, margins and alignment, defined once in a style table and applied to every line.

Players with a full ASS renderer, including mpv, VLC and MPC-HC through libass or similar engines, follow that style, so the subtitles look the same on every machine that has the font. The same file is what you hand to ffmpeg or HandBrake when captions must be burned into a video for social media, where uploads often have no subtitle track at all. The subtitle converter offers ASS for exactly these jobs.

One thing ASS cannot do is guess what the SRT never stored. Speakers, sign text and song lines all arrive as plain dialogue in the Default style, because SRT has no way to tell them apart. If you are preparing a release, convert first, open the .ass in Aegisub, assign styles to the song and sign lines, then mux it into the video. For playback on devices that dislike MKV, MKV to MP4 converts the video, though most MP4 players ignore a styled ASS track.