Re: Media Fragments in Opera

On Thu, Oct 21, 2010 at 1:57 AM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Wed, 20 Oct 2010 11:48:15 +0200, Conrad Parker <conrad@metadecks.org>
> wrote:
>
>> On 18 October 2010 17:55, Philip Jägenstedt <philipj@opera.com> wrote:
>>>
>>> For those of you who were not at FOMS, here's a little FYI:
>>>
>>> The first native browser implementation of Media Fragments was demoed at
>>> FOMS, that is: something I hacked into Opera. This is not ready to ship,
>>> so
>>> don't expect to see it in desktop Opera just yet. Here's some
>>> implementation
>>> feedback:
>>>
>>> About t:
>>>
>>> * We should consider making the HH component optional. Most clips online
>>> are
>>> less than an hour, and being able to say #t=9:23 would be useful.
>>>
>>> * It's not clear to me what to do with the smpte formats. In our
>>> underlying
>>> media framework (GStreamer) time is expressed in nanoseconds, so it
>>> doesn't
>>> actually give any great precision that using 9 decimals. For now, I've
>>> not
>>> added support for the smpte formats at all. Are there any existing
>>> implementations or indications that anyone does want to implement it?
>>>
>>> * The use case for 'clock' syntax is pretty clear, but AFAIK the time in
>>> UTC
>>> isn't available in Ogg or WebM, so I'm not sure what to do with it.
>>>
>>> (In short, I've only implemented the npt syntax.)
>>>
>>
>> I was thinking that the smpte formats would be useful for applications
>> that need to address specific frames, such as web-based video editors.
>> Humans may not find these formats so necessary. It may be the case
>> that something like Metavid is already advanced enough to do
>> frame-level editing.
>
> My issue with this syntax is that the actual media frameworks that one
> inevitably uses to implement it don't support addressing frames like this,
> they simply deal in nanoseconds or similar. (This is true of at least
> GStreamer and DirectShow.) If using the SMPTE syntax doesn't, in practice,
> give you greater precision than using more decimals, is it worthwhile?
>
> For video editing in the browser, I think that would best be built using the
> JavaScript API, possibly with some additions to allow frame- and
> sample-accurate offsets if that turns out to be a problem. It seems
> premature to try to solve the problem using MF.

I don't remember where it came from, but there were user requests and
requirements that asked for SMPTE syntax - we weren't going to do it
at first. It may have come from live streaming, TV style applications,
video editing, or something else. SMPTE is unfortunately still the
standard for much TV-related and professional video stuff, so we
shouldn't ignore it. Also, it's actually not that difficult to convert
between SMPTE and ms, so just regard SMPTE as a "marker" for certain
ms offsets (similar to UTC in fact). I have some functions here that
might help: http://svn.annodex.net/libcmml/trunk/src/cmml_time.c .

Cheers,
Silvia.

Received on Wednesday, 20 October 2010 21:08:47 UTC