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Re: [MSE] non fragmented MP4

From: Aaron Colwell <acolwell@google.com>
Date: Thu, 14 Feb 2013 14:35:10 -0800
Message-ID: <CAA0c1bCcs=JPqKvdS90g1PfY8RGo1jassM41_G4qxpq9VypYqA@mail.gmail.com>
To: Giuseppe Pascale <giuseppep@opera.com>
Cc: "<public-html-media@w3.org>" <public-html-media@w3.org>
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. 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.

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
>
>
Received on Thursday, 14 February 2013 22:35:41 UTC

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