What are the common subtitle formats?
Text subtitles
SRT(.srt)
SubRip Text (SRT) is a widely supported and simple format, it consists of a plain text file that contains time codes for each subtitle, the text of the subtitle, and a sequence number indicating the order of the subtitles.
ASS/SSA(.ass/.ssa)
It is an advanced subtitle format that allows you to control many text parameters: font format, color, height, transparency, text location on frames. This format is quite popular and is widely supported by players along with SRT
SAMI (.smi)
SAMI(Synchronised Accessible Media Interchange) is a Microsoft official format,this is the only format that standard Windows Media Player can play.
WebVTT (.vtt)
WebVTT is used on web pages and many video platforms, like YouTube, use this format to display closed captions in streaming video,it is based on SRT.
DVD(Vobsub) and Blu-ray subtitles
VobSub (idx+sub)
VobSub basically just re-packages the images from the DVD into a file that has the extension of .SUB and additional information in another file with an extension of .IDX. Information in the IDX file tells media player software the color of the subtitles, their position on the screen, when they appear and disappear, and a number of other important pieces of information.
PGS(.sup)
PGS(Presentation Graphic Stream) is a type of subtitle commonly used on Blu-rays, HD DVDs and normal DVDs. Sup subtitles contain images of text instead. With sup subtitles you'll never have issues with text encoding or missing fonts for exotic languages.