Timed track formats

Lists of formats:

• http://wiki.videolan.org/Subtitles_codecs
• http://en.wikipedia.org/wiki/Subtitle_(captioning)#For_software_video_players

Requirements:

• We need to use time for timings, not frames, because the same file might apply to multiple versions of the same video, with different frame rates.
• For a similar reason, any positioning needs to be relative to the frame, not absolute (in pixels)

(Extensions marked * below are shared by multiple formats.)

AQTitle (.aqt)

Uses frames for timings.

JACOSub (.jss)

• http://unicorn.us.com/jacosub/jscripts.html
• http://unicorn.us.com/jacosub/demo.txt

Pretty complicated. Uses "\n" for line breaks.

Kate

• http://wiki.xiph.org/OggKate#Format_specification ?

Binary format with text components, making it hard to hand-edit. The text components seem pretty verbose.

MicroDVD (.sub*)

• http://en.wikipedia.org/wiki/MicroDVD
• http://divxstation.com/article.asp?aId=27

Uses frames for timings. Uses "|" for line breaks.

(Appears to be basically the PowerDivX format, but using seconds instead of frames.)

MPEG-4 Timed Text (.ttxt)

• http://gpac.sourceforge.net/doc_ttxt.php

Pretty complicated. Seems to be formatting-centric. Has some pixel-based positioning. Difficult to hand-edit. Uses strings delimited by apostrophes to mark line breaks.

MPSub (.sub*)

• http://www.mplayerhq.hu/DOCS/tech/mpsub.sub

Relative timings, which can be hard to hand-edit correctly. Uses real line breaks. Could be extended, though most useful extensions would not be backwards-compatible (e.g. adding a new timing format).

Ogg Writ

• http://wiki.xiph.org/OggWrit

Binary format, nigh on impossible to hand-edit.

Phoenix Subtitle (.pjs)

• No spec or demo file found

Uses frames for timings according to wikipedia.

PowerDivX (.psb)

• Could not find specification
• Sample file: http://femmefontaine.org/en_sub/ff_1_4.psb (note: explicit content)

Currently has low resolution timings. Uses "|" for line breaks. Simple format. Could be extended usefully.

(Appears to be basically the MicroDVD format, but using seconds instead of frames.)

RealText (.rt)

• http://service.real.com/help/library/guides/realtext/realtext.htm

Supports a number of features that aren't necessary. Uses "<br/>" for line breaks. Could probably be used as the basis for a new similar format.

SAMI (.smi)

• http://en.wikipedia.org/wiki/SAMI

Probably has complicated legacy parsing requirements. Uses "<BR>" for line breaks. Would be difficult to extend in a backwards-compatible way.

Structured Subtitle Format (.ssf)

Couldn't find any information on this format.

SubRip (.srt)

• http://forum.doom9.org/archive/index.php/t-73953.html

Currently has pixel-based positioning. Simple format. Uses real line breaks. Could be extended usefully.

Gloss Subtitle (.gsub)

Couldn't find any information on this format.

SubStation Alpha (.ssa)

• http://www.matroska.org/technical/specs/subtitles/ssa.html

Pretty verbose. Has some pixel-based positioning. Uses "\N" for line breaks (though this is somewhat configurable). Has some rather subtle syntax of the kind that typically results in buggy implementations. (Indeed, see the "note" in [1].)

Advanced SubStation Alpha (.ass)

Even more complicated version of SubStation Alpha.

SubViewer (.sub*)

• http://wiki.videolan.org/SubViewer

Simple format. Uses "[br]" for line breaks. Could be extended usefully.

Universal Subtitle Format (.usf)

• Couldn't find any official documentation
• http://blog.aegisub.org/2008/07/universal-subtitle-format-post-mortem.html

Extremely verbose. Uses "<br/>" for line breaks.

Other formats

CMML and SMIL are not listed above since they don't appear to be subtitle formats so much as timed media mixing formats.