Re: meta-data in the VTT file header, a strawman proposal

On Apr 23, 2012, at 16:00 , Glenn Maynard wrote:

> On Sat, Apr 21, 2012 at 1:10 AM, Silvia Pfeiffer <silviapfeiffer1@gmail.com> wrote:
> Something like:
> 
> 1.
> Name-vaue pairs of header metadata are given with a name-string
> separated from the value by a colon.
> No control characters or separators are allowed in the name value.
> No white space is allowed between the name and the colon (?).
> 
> 2.
> If the value is a single "|" character, the value is multi-line,
> starting on the next line and ends with a line that only contains a
> single dot.
> The newline just before the dot-line is also not part of the value.
> 
> 
> A quick-and-dirty ABF could be:
> 
> metadata-header = field-name ":" field-value
> field-name = token
> field-value = ("|" *TEXT CRLF "." CRLF) | (*TEXT without CRLF)
> 
> (I'm not sure; it looks more or less right, but reading ABFs has always given me a headache.)
> 
> Some other details:
> 
> Presumably, whitespace between the colon and a single-line value would be stripped, eg.
> 
> Key:     Value
> 
> would result in "Key" = "Value".  If you have significant leading whitespace in the value you want to preserve, or if you need to encode the string "|" itself, then switch to the block format:
> 
> Key: |
>     Value
> .
> 
> Key: |
> |
> .


Yes.  Then all we need to add is
"In multi-line values, a line that either (a) starts with the escape character or (b) is blank (safer, visually blank) or (c) consists of the termination sequence (a single period) must be escaped by having a "\" pre-pended. On receipt, gather the lines up to the final terminator (".") and remove all leading "\" characters. 

If we want total flexibility, remove the line-break before the "." line, so you can end without the line-end character if you want to (you can always put it back explicitly with an escaped blank line). 

David Singer
Multimedia and Software Standards, Apple Inc.