79 lines
3.4 KiB
Markdown
79 lines
3.4 KiB
Markdown
# Flipnote Subtitle format, version 1
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- File extension: `.fsrt`
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- Encoding: UTF-8, with an optional UTF-8 byte order mark at the start
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- Line endings: LF or CRLF (readers may also accept CR)
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## Cue blocks
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A file contains one or more cue blocks, separated by an empty line. A line
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containing only spaces or tabs also counts as a separator.
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Each block consists of:
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1. A positive decimal sequence number.
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2. A page range written as `start --> end`.
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3. One or more non-empty lines of subtitle text.
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Sequence numbers identify blocks for people editing the file. They do not
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determine timing. Writers number blocks consecutively from 1; readers may
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accept non-consecutive numbers and out-of-order blocks.
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Sequence numbers may not exceed 9,007,199,254,740,991.
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## Page ranges
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Pages are animation frames, numbered from 1. Both ends of a range are included.
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`3 --> 3` is valid and appears on page 3 only. Gaps between cues have no subtitle.
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`start` and `end` must be positive decimal integers, with `end >= start`.
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For compatibility with JavaScript readers, neither may exceed 9,007,199,254,740,991.
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Readers must reject overlapping ranges. Adjacent ranges such as `1 --> 4` and
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`5 --> 8` do not overlap.
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Spaces and tabs around the page numbers and arrow are allowed. There are no
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timestamps, frame-rate declarations or cue settings on this line. A reader
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must not silently interpret an ordinary SRT timestamp as a page number.
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Applications should check that all ranges fit their target Flipnote. Timing
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depends on pages, so it follows the Flipnote when its playback speed changes.
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## Text
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Text is Unicode and is displayed literally. Tags such as `<b>` have no special
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meaning. There is no escaping syntax, markup, positioning, font selection or
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colour information. Blank lines delimit cues and cannot occur within text.
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Leading and trailing spaces on non-empty text lines are preserved.
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Text must be valid UTF-8; unpaired UTF-16 surrogates are not valid text.
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Tabs are allowed. Other C0 control characters, except line endings, and DEL
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are invalid. Applications may restrict characters or line lengths to fit their
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fonts and display. They should report unsupported text rather than silently
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discard it.
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## Languages and media
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One file is one language track. Language is not stored inside the file. A
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filename can include a language code, for example `animation.ar.fsrt`, but
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the importing application must let the user choose the language.
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It may present the available files as separately selectable tracks rather
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than assigning language codes to them.
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An FSRT contains neither the animation nor its audio. It doesn't carry an
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author identity, signature, account token or link to a particular PPM. The
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user chooses the Flipnote it belongs to.
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## Writer output
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The reference writers sort cues by starting page, use consecutive sequence
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numbers, put one space on each side of `-->`, and emit LF line endings with
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one empty line between cues and one final newline. These choices keep diffs
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readable; other accepted spacing and line endings remain valid.
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## Reference parser limits
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The JavaScript and Python implementations limit input and output to 1 MiB
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(1,048,576 UTF-8 bytes), with a default maximum of 10,000 cues. These are
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resource limits of the reference code, not additional fields in the format.
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Applications can set lower page and cue limits. Invalid data must be reported
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as an error rather than silently clipped, truncated or interpreted as HTML.
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