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Re: [MSE] non fragmented MP4

From: Giuseppe Pascale <giuseppep@opera.com>
Date: Fri, 15 Feb 2013 11:38:13 -0000
To: "Aaron Colwell" <acolwell@google.com>
Cc: "<public-html-media@w3.org>" <public-html-media@w3.org>
Message-ID: <op.wsjmhzmn6ugkrk@giuseppep-x220>
On Thu, 14 Feb 2013 22:35:10 -0000, Aaron Colwell <acolwell@google.com>  

> 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?

> 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

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?


> 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
Received on Friday, 15 February 2013 10:38:48 UTC

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