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Re: [ttml2] embedded content, background image styling, other edits

From: Glenn Adams <glenn@skynav.com>
Date: Wed, 26 Nov 2014 07:23:11 -0700
Message-ID: <CACQ=j+dqGs8hgrHuqR6sgfcZnvaqMg4Zr1qZbL3t+5+=a4OdKA@mail.gmail.com>
To: John Birch <John.Birch@screensystems.tv>
Cc: TTWG <public-tt@w3.org>, Andreas Tai <tai@irt.de>, Nigel Megitt <nigel.megitt@bbc.co.uk>
On Wed, Nov 26, 2014 at 4:20 AM, John Birch <John.Birch@screensystems.tv>
wrote:

>  Hi Glenn,
>
>
>
> Apologies for ‘splitting the thread’ but I wanted to comment on two
> specifics in your earlier email…
>
>
>
> Re: In the above example, charset is a parameter of the MIME type
> expression of the *type* attribute. No relationship with the 'encoding'
> attribute.
>
>
>
> How easy it is to misread a ; as a “ !  ;-) My subsequent comments were
> based on that misinterpretation, but thanks for the confirmation that I
> perhaps understand the use of encoding correctly J.
>
>
>
> Re: I guess you are thinking chunk might be used to contain multiple
> original files (separately named) that are concatenated to form a single
> data resource. This is counter to my intention that a chunk contain a
> fragment of a data resource, or, if one wished, an entire data resource (if
> a data element has a single chunk child like in the above example).
>
>
>
> Yes, that is exactly what I was thinking… I’m assuming that you would
> suggest that my multiple files would each be represented by separate data
> elements?
>

Exactly.


> The problem I have with that is that the separate ‘files’ in my example
> actually form a single resource from the perspective of EBU-TT…
>

I don't wish to break the very common understanding that resources and
files are 1:1. If you want to divide a file into multiple files that are
related to one another, then you need to use something else to link them
together. Nigel has proposed such a mechanism in CP25
<https://www.w3.org/wiki/TTML/changeProposal025>. See also Issue 288
<http://www.w3.org/AudioVideo/TT/tracker/issues/288>.

The chunk child of data is not intended to address this use case.


> i.e. the STL standard defines the concept of a primary file and optional
> extension files that are conceptually part of the whole. I have attached
> the relevant specification FYI. This is admittedly a marginal use case, as
> I  have never seen a ‘subtitle list’ that spans multiple ‘disks’ !
>
>
>
> However, I didn’t see anything in the definition of chunks that precludes
> it being used in the way I proposed? Did I miss something?
>

It is conceptually not intended to handle this case. Further, chunk allows
only #PCDATA content, so no metadata children where you might use the new
ttm:item element to link to some external identifier.

My conceptual model for chunks was the HTTP 1.1 chunked transfer encoding
[1].

[1] http://tools.ietf.org/html/rfc2616#section-3.6.1


>
>
> Best regards,
>
> John
>
>
>
>
>
>
> *John Birch | Strategic Partnerships Manager | Screen *Main Line : +44
> 1473 831700 | Ext : 2208 | Direct Dial : +44 1473 834532
> Mobile : +44 7919 558380 | Fax : +44 1473 830078
> John.Birch@screensystems.tv | www.screensystems.tv |
> https://twitter.com/screensystems
>
>
> *Visit us at BVE, Excel London 24-26 February 2015 Stand No. N19*
>
> *P** Before printing, think about the environment*
>
> *From:* Glenn Adams [mailto:glenn@skynav.com]
> *Sent:* 25 November 2014 17:12
> *To:* John Birch
> *Cc:* TTWG; Andreas Tai; Nigel Megitt
> *Subject:* Re: [ttml2] embedded content, background image styling, other
> edits
>
>
>
> Thanks for your review and input.
>
>
>
> On Tue, Nov 25, 2014 at 2:43 AM, John Birch <John.Birch@screensystems.tv>
> wrote:
>
> Hi Glenn,
>
>
>
> I’ve been looking at your proposal for embedded content (and I like it J
> but I noticed the following:
>
>
>
> ...
>
> <data type="text/plain; charset=us-ascii" length="44">
>
>   <chunk length="19">
>
>     VGhlIHF1aWNrIGJyb3duIGZveA==
>
>   </chunk>
>
>   <chunk length="25">
>
>     IGp1bXBzIG92ZXIgdGhlIGxhenkgZG9nLg==
>
>   </chunk>
>
> </data>
>
> ...
>
>
>
> I don’t see ‘charset’ as an attribute of data in the later definition…
>
>
>
> In the above example, charset is a parameter of the MIME type expression
> of the *type* attribute. No relationship with the 'encoding' attribute.
>
>
>
>  I thought initially this was a typo and that it should be encoding, but
> then realised that ‘encoding’ is not permitted on the parent data element
> when using chunks?
>
>
>
> Correct, 'encoding' is permitted only on the data element when the content
> of the data element uses simple data embedding, i.e., consists only of
> #PCDATA that encodes the data bytes. If a data element uses chunked data
> embedding, i.e., uses chunk element children, then all of the encoded data
> bytes are in child chunk elements, so the encoding attribute applies only
> to the chunk children and not the data parent.
>
>
>
> In the above example, the encoding attribute's default value 'base64'
> applies on the chunk children, and is not relevant on the data parent.
>
>
>
>
>
>  However, the binaryData element in EBU-TT includes an attribute that
> does not appear within your proposed scheme, which is the fileName
> attribute. This optional attribute may contain “A filename that may be used
> to identify the original filename of the tunnelled binary data”.
>
>
>
> I'm not sure there is a useful use case for formalizing such a
> name/identifier. It wouldn't have any relevant processing semantics in
> TTML2, so it is definitely in the metadata category, which means using a
> ttm:* attribute or a metadata element, e.g., one could use the following
> convention with ttm:desc.
>
>
>
> <data type='application/octet-stream'>
>
>   <metadata>
>
>     <ttm:desc>original_file_name=foo.bar</ttm:desc>
>
>   </metadata>
>
>   <chunk>
>
>   ... encoded base64 data ...
>
>   </chunk>
>
> </data>
>
>
>
> I wouldn't mind adding a new ttm:* element that generalizes the task of
> defining metadata parameters, e.g.,
>
>
>
> <ttm:parameter name='fileName'>foo.bar</ttm:parameter>
>
>
>
> which would allow rewriting the above example to
>
>
>
> <data type='application/octet-stream'>
>
>   <metadata>
>
>     <ttm:parameter name='original_file_name'>foo.bar</ttm:parameter>
>
>   </metadata>
>
>   <chunk>
>
>   ... encoded base64 data ...
>
>   </chunk>
>
> </data>
>
>
>
>  *There is some discussion as to the usage of this element, it could be
> viewed as metadata of ‘historic interest’ (e.g. the name of the DOS file
> that is encapsulated by the binary data) or it could be seen as a directive
> (i.e. what to name a file should a processor re-create a file from the
> binary data). My personal leanings are towards the former use…*
>
>
>
> Regardless of the use of this attribute, I would like to propose that the
> TTWG consider adding a similar attribute to the data *and chunk* elements
> in TTWG. (*As an aside the chunk element you propose would be a better
> resolution to one of the original EBU-TT requirements where multiple floppy
> disk based DOS files make up an STL document.*) Clearly the name
> ‘fileName’ would be inappropriate in a more generic specification but I
> tentatively suggest the following (below).
>
>
>
> We could consider it. But it definitely would not be appropriate on chunk,
> which sole purpose is to enable streaming of data fragment children of a
> data element. I guess you are thinking chunk might be used to contain
> multiple original files (separately named) that are concatenated to form a
> single data resource. This is counter to my intention that a chunk contain
> a fragment of a data resource, or, if one wished, an entire data resource
> (if a data element has a single chunk child like in the above example).
>
>
>
>
>
> Best regards,
>
> John
>
>
>
>
>
> <chunk
>
>   encoding
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-attribute-encoding>
> = (base16|base32|base32hex|base64|base64url) : base64
>
>   length = xsd:nonNegativeInteger
> <http://www.w3.org/TR/xmlschema-2/#nonNegativeInteger>
>
>   xml:id
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#content-attribute-id>
> = ID
>
>   ident = xs:string
>
>   {*any attribute not in default or any TT namespace*}>
>
>   *Content:* #PCDATA
>
> </chunk>
>
>
>
> An ident attribute may be specified, and may contain an identifier for the
> contained data from an external context (e.g. the original filename).
>
>
>
> And
>
> <data
>
>   encoding
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-attribute-encoding>
> = (base16|base32|base32hex|base64|base64url) : *see prose below*
>
>   format
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-attribute-format>
> = <data-format>
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-value-data-format>
>
>   length = xsd:nonNegativeInteger
> <http://www.w3.org/TR/xmlschema-2/#nonNegativeInteger>
>
>   src
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-attribute-src>
> = <data>
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-value-data>
>
>   type
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-attribute-type>
> = xsd:string <http://www.w3.org/TR/xmlschema-2/#string> : *see prose
> below*
>
>   xml:id
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#content-attribute-id>
> = ID
>
>   ident = xs:string
>
>   xml:lang
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#content-attribute-lang>
> = xsd:string <http://www.w3.org/TR/xmlschema-2/#string>
>
>   xml:space
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#content-attribute-space>
> = (*default*|*preserve*)
>
>   {*any attribute not in default or any TT namespace*}>
>
>   *Content:* #PCDATA | (Metadata.class
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#element-vocab-group-metadata>*,
> chunk
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-vocabulary-chunk>+)
> | (Metadata.class
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#element-vocab-group-metadata>*,
> source
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-vocabulary-source>
> +)
>
> </data>
>
>
>
> If simple data embedding is used, i.e., the content of the data element
> is one or more text nodes, then an ident attribute may be specified, and
> may contain an identifier for the contained data from an external context
> (e.g. the original filename). If chunked or sourced data embedding is used,
> i.e., the content of the data element contains any child chunk
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-vocabulary-chunk>
> or source
> <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#embedded-content-vocabulary-source>
> element, then an ident attribute must not be specified.
>
>
>
>
>
>
> *John Birch | Strategic Partnerships Manager | Screen *Main Line : +44
> 1473 831700 | Ext : 2208 | Direct Dial : +44 1473 834532
> Mobile : +44 7919 558380 | Fax : +44 1473 830078
> John.Birch@screensystems.tv | www.screensystems.tv |
> https://twitter.com/screensystems
>
>
> *Visit us at BVE, Excel London 24-26 February 2015 Stand No. N19*
>
> *P** Before printing, think about the environment*
>
>
>
> *From:* Glenn Adams [mailto:glenn@skynav.com]
> *Sent:* 23 November 2014 22:50
> *To:* TTWG
> *Subject:* [ttml2] embedded content, background image styling, other edits
>
>
>
> I've updated the TTML2 ED [1] a few times in the last few days to:
>
>    - add embedded content element types (new section 9)
>
>
>     - audio
>       - chunk
>       - data
>       - font
>       - image
>       - resources
>       - source
>
>
>    - add background image styling
>
>
>     - tts:backgroundImage
>       - tts:backgroundRepeat
>       - tts:backgroundPosition
>
>
>    - sub-divide former parameters section into profiles section and
>    parameters section
>
>  For detailed diffs, see change sets [2][3][4][5][6].
>
>
>
> [1] https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html
>
> [2] https://dvcs.w3.org/hg/ttml/rev/d16d284100b9
>
> [3] https://dvcs.w3.org/hg/ttml/rev/67327764d375
>
> [4] https://dvcs.w3.org/hg/ttml/rev/25035c814da5
>
> [5] https://dvcs.w3.org/hg/ttml/rev/cc2b7aad7e7a
>
> [6] https://dvcs.w3.org/hg/ttml/rev/e3fdbceb09cb
>
>
>
>
>
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> Registered Office: The Old Rectory, Claydon Church Lane, Claydon, Ipswich,
> Suffolk, IP6 0EQ
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Received on Wednesday, 26 November 2014 14:24:00 UTC

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