Re: [MSE] non fragmented MP4

Comments inline...


On Fri, Feb 15, 2013 at 3:38 AM, Giuseppe Pascale <giuseppep@opera.com>wrote:

> **
> On Thu, 14 Feb 2013 22:35:10 -0000, Aaron Colwell <acolwell@google.com>
> wrote:
>
> Hi Giuseppe,
>
> There are no current plans to support non-fragmented MP4 files. One thing
> to remember is that MSE  accepts byte streams and not files per se. For MP4
> we use the fragmented format because it allows segments of the timeline to
> be appended easily and in any order. Supporting non-fragmented files would
> require the UA to hold the whole file in memory which could be very
> problematic on memory constrained devices. If the UA decides to garbage
> collect part of the presentation timeline to free up space for new appends
> it is not clear how the web application could reappend the garbage
> collected regions without appending the whole file again.
>
>
> Wouldn't the use of Stream object (appenStream() ) partially attenuate
> this concern or at least allow for optimizations?
>

[acolwell] Not really. Stream is a bytestream abstraction so from MSE's
point of view it just sees a stream of bytes and has no idea where they are
coming from or whether the underlying source of the bytes can be accessed
in a non-sequential manner.


>
>
> The fragmented form allows the application to easily select the desired
> segment and reappend it. Applications can control the level of duplicate
> appending by adjusting the fragment size appropriately. Non-fragmented
> files are so permissive about how they can store samples, there is no
> simple way to collect segments of the timeline w/o essentially exposing a
> random access file API.
>
>
> Advantages of using fragmented mp4 are clear. the problem is that for the
> use case I'm looking at (ads insertion) not always the content (the ad) is
> available as a fragmented mp4. BTW being an add typically not too long,
> this could partially attenuate the concern about memory consumption
>

[acolwell] My expectation is that the web application using MSE will make
sure that all the content it intends to use in a presentation is in
fragmented format.

[acolwell] The ad being "not too long" is a slippery slope. By saying MSE
supports non-fragmented MP4 it opens up the door to many interpretations of
what is an acceptable length. If the content owner is forced to reformat to
fragmented form it forces them to consider how big the fragments should be
and then it is much easier to deal with the problem because you can always
make the fragments smaller independent of the duration of the media you are
trying to append.



>
> Is there a way we could cater for this use case? Or is the only solution
> to basically consider the whole file as a big media segment?
>

[acolwell] In my opinion the ad's should just be remuxed to fragmented form
as part of the ingest process. Tools like
GPAC<http://gpac.wp.mines-telecom.fr/>make this super easy.

Aaron


>
> /g
>
>
>
> Aaron
>
>
> On Thu, Feb 14, 2013 at 4:19 AM, Giuseppe Pascale <giuseppep@opera.com>wrote:
>
>> Hi,
>> is not clear to me if MSE has provision for supporting also non
>> fragmented MP4 files (section 8.2 only seems to describe fragmented MP4).
>>
>> Can someone give me some hints? Is alternating fragmented and non
>> fragmented mp4 files one of the use cases that you have considered? How
>> would that work?
>>
>> /g
>>
>>
>>
>> --
>> Giuseppe Pascale
>> Product Manager TV & Connected Devices
>> Opera Software
>>
>>
>
>
>
> --
> Giuseppe Pascale
> Product Manager TV & Connected Devices
> Opera Software
>