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Re: contentType: Are codecs allowed? Use a simpler string to identify the initData format?

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sat, 11 Jan 2014 11:46:36 +1100
Message-ID: <CAHp8n2n8dNfao1MShi6+HPTT=2Qx4beXxX-n6L-dE7aw=qiD2g@mail.gmail.com>
To: David Dorwin <ddorwin@google.com>
Cc: "<public-html-media@w3.org>" <public-html-media@w3.org>, Dave Singer <singer@apple.com>, Xiaohan Wang (王消寒) <xhwang@google.com>
On 11 Jan 2014 05:41, "David Dorwin" <ddorwin@google.com> wrote:
> I agree that the extra parameters are generally useful. In these cases,
though, we just want to know whether the data came from a WebM or MP4 or
etc. stream. Supporting both audio/mp4 and video/mp4 works - it's just
unnecessary complexity in every UA and application.
> One option for eliminating that complexity would be to specify that when
there are audio/ and video/ variants, the video/ variant should always be
used. It seems likely that UA implementations might always do so for the
needkey event anyway.

Why not make this a quality of  implementation issue. You just need a regex
that finds "/mp4" in the string and be done. Then users can use as much of
the mime type as they want. Might be easier for js devs than having to
manipulate the mime string to fit with what browsers expect.

Just my 2c worth.

> At a minimum, we should disallow anything other than type/subtype so that
simple string comparisons can be used. Does it make sense to reference RFC
2045 with something like the following?
>> contentType should be a 'type "/" subtype' string as defined for
the Content-Type Header Field specified in RFC 2045 without any additional
"parameter" values.
>> <non-normative>That is, contentType should not contain 'codecs' or
> With the reference to "Content-Type", the attribute/parameter name
"contentType" makes a lot of sense as the parameter/attribute name. Even
though isTypeSupported() also accepts valid Content-Type values, I think we
should revert the name of the parameter to |type| to differentiate
the intended use and be consistent with canPlayType and
MSE's isTypeSupported().
> David
> On Wed, Jan 8, 2014 at 5:09 PM, Xiaohan Wang (王消寒) <xhwang@google.com>
>> If we decide to go with the proposed
>> createSession(DOMString initDataType, Uint8Array initData);
>> Can we change the order of the two parameters so that we have
>> createSession(Uint8Array initData, DOMString initDataType) ?
>> It seems more natural to me to have (data, datatype) than the other way.
>> Xiaohan
>> On Wed, Jan 8, 2014 at 9:53 AM, David Singer <singer@apple.com> wrote:
>>> I am not sure that I agree here.
>>> The reason that we use MIME types is that they have a registry and
well-defined meanings.  I really don’t want to use ‘casual’ names here, and
I really don’t want to invent another registry.
>>> The extra parameters are absolutely useful for any of the many formats
that are ‘general containers’ such as AVI, QT, MP4, 3GPP, and so on;  when
you are determining, for example, if you can play a file, knowing (at
least) the codecs in it is kinda important.  The MIME extensions (‘buckets
RFC, 6381) was written for a good reason.
>>> I am fine with restricting it to a simple type in contexts where that’s
all that is plausibly needed, of course.
>>> I don’t think it’s very hard to recognize both (for example) audio/mp4
and video/mp4, is it?
>>> Am I missing something (and if so, I apologize)?
>>> On Jan 7, 2014, at 18:17 , David Dorwin <ddorwin@google.com> wrote:
>>> > [Note: |type| was renamed to |contentType| this morning to resolve
bug 24213.]
>>> >
>>> > I have always assumed that contentType - as reported in the needkey
event and passed to createSession() - would be a simple MIME type
containing only the container type. For example, "video/webm" or
"audio/mp4". However, I don't think the spec actually has this restriction.
>>> >
>>> > Such a restriction would make both browser and app implementations
simpler (and slightly reduce confusion about the meaning of the values). I
suppose it's possible that an app developer might want to pass the same
codec-containing string to isTypeSupported() and createSession(), but at
the cost of forcing all apps to parse the value rather than doing a simple
string compare. Does anyone object to adding an explicit restriction?
>>> >
>>> > The use of "MIME type" also means that the needkey event could report
either the audio/ or video/ variant regardless of the actual stream(s) in
the media data. This is noted twice in the spec (example). Maybe this all
would be simpler if we stopped using a MIME type and just passed the
container name. such as "webm" or "mp4". The exact string to use would be
specified in the relevant Container Guidelines. (We could potentially even
use "cenc" and avoid the ambiguity discussed in bug 17673.)
>>> >
>>> > Given the intended values and use, I wonder if we should change the
|contentType| attribute and parameter name to |containerType| or just
|container|. |initDataType| is another option, since that's really what the
value indicates. (This makes even more sense if we use just the container
name as discussed above.) We could revert then isTypeSupported()'s
parameter name to |type| to again be consistent with canPlayType() and
MSE's isTypeSupported(), all of which accept full MIME types with optional
>>> >
>>> > If we made both changes, we would have the following signatures:
>>> > static bool isTypeSupported(DOMstring keySystem, DOMString? type);
>>> > MediaKeyNeededEvent.initDataType
>>> > MediaKeySession createSession(DOMString initDataType, Uint8Array
>>> > Example uses:
>>> > MediaKeys.isTypeSupported('org.w3.clearkey', 'video/mp4');  //
>>> > MediaKeys.isTypeSupported('org.w3.clearkey', 'video/mp4;
codecs="avc1"');  // Unchanged
>>> > if (event.initDataType = 'mp4') {...}
>>> > MediaKeys.createSession(event.initDataType, event.initData);
>>> > MediaKeys.createSession('mp4', initDataArray);
>>> >
>>> > Thoughts? Other suggestions?
>>> >
>>> > David
>>> David Singer
>>> Multimedia and Software Standards, Apple Inc.
Received on Saturday, 11 January 2014 00:47:04 UTC

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