[Mp4-tech] Necessity of IODS

Fri Jan 25 09:57:06 EST 2008

Praveen,
The Initial Object Descriptor is fully specified in the ISO/IEC 14496-1
a.k.a. System part of MPEG-4 and "defined" as:
"A special object descriptor that allows the receiving terminal to gain
initial access to portions of content encoded according to ISO/IEC
14496. It conveys profile and level information to describe the
complexity of the content."
In other words in my understanding, it does somewhat specify what you
should be expecting on a receive side in terms of requirements (e.g.
decoding capabilities/memory/complexity/sync) for a decoding
device/terminal to be able to receive and decode a specified combination
of arriving elementary streams of various types like video, audio,
graphics, text etc... In theory, you might be able to learn from IOD
that you're about to receive a combination of multiple elementary
streams of the same type, for example 2 videos + 4 audios along with a
real-time updated graphics content. More specifically, an IOD will
provide you among others the following information for each stream type:
max_bitrate, avg_bitrate, priority, buffer_size. In addition, you should
be able to learn about synchronization between streams from IOD. And
then you can also learn more about stream specific decoding needs for
any embedded elementary bitstream as video or audio, if their "decoding
descriptors" are also included. I believe all of that information holds
true, but it was sometime ago, when I was involved with...
You might want to study, as mentioned below, ISMA Spec. as a good
strating point and to review code of http://mpeg4ip.sourceforge.net/
Good luck! and best regards,
Andrew
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Praveen Singh
Sent: Friday, January 25, 2024 6:55 AM
To: Richard Sotke
Cc: mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] Necessity of IODS
Hi Richard,
thanks again, your reply helped me a lot.
Now i am having following issues:
1. For mp4 file, the InitialObjectDescriptor(mp4_IOD_Tag) contains some
profile and level indications (ISO/IEC 14496-1). a)What will be the use
of that information (levels and profiles) to parse the file. b)How i can
extract trak(BIFS) and trak(OD) inormation from that. c)And where i can
get the detail description regerding that.
2. When i converted few 3gp files to mp4 files through MP4Box, the
contains of "esds' box is got changed(e.g. maxBitrate and avgBitrate
fields of DecoderConfigDescriptor became 0). I could not understand the
reason behind that?
Praveen
-----Original Message-----
From: Richard Sotke [mailto:richard sotke.de]
Sent: Thursday, January 24, 2024 4:21 PM
To: mp4-tech lists.mpegif.org; Praveen Singh
Subject: Re: [Mp4-tech] Necessity of IODS
Am Donnerstag, 24. Januar 2008 06:05:44 schrieb Praveen Singh:
> Hi Richard,
> thanks a ton.
> I have the 3gp file format parsing library with me. Now to make it 
> able to parse mp4 files, i need to add "iods" parsing.
What exactly do you want to support?
Do you want playback most common files around? Most files around don't
use the Object Descriptor Framework, so if your strict, they are not MP4
files(ISO/IEC 14496-14). Or do you plan to use features based at the
Object Descriptor Framework?
> But how it will be able to parse mp4 file that do not have "iods" box?

> Are the mp4 files without "iods" boxes (sub part of a presentation)
Forget about MP4 files which are a sub part of a presentation for now,
they are not used alone.
> are exactly  same as 3gp files(apart from brand etc.)? Can they be 
> parsed
by
>3gp parser?
Dependent on your 3gp parser you should be able to archive your goal,
parsing of ISO base media format compatible files(ISO/IEC 14496-12),
with it.
>
> And can u tell me where i will get the mp4 video files having iods 
> box. I have downloaded more than 50 video files but none of them 
> contains the iods box.
You can create MP4 files with IOD with MP4Box from
http://gpac.sourceforge.net/ . Simple ISMA 1.0 compatibele files created
with should containe an IOD. You can also take a look at libgpac which
comes with support for the Object Descriptor Framework, but I guess it
is not what your are looking for.
The Documentatiion at GPAC may be from interest too.
>
> Praveen

Regards
Richard
>
> -----Original Message-----
> From: mp4-tech-bounces lists.mpegif.org 
> [mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Richard Sotke
> Sent: Wednesday, January 23, 2024 2:24 PM
> To: mp4-tech lists.mpegif.org
> Subject: Re: [Mp4-tech] Necessity of IODS
>
> Am Mittwoch, 23. Januar 2008 06:49:19 schrieb Praveen Singh:
> > Hi all,
> > I am working on mp4 parser library.
> > When standards says that mp4 follows the Object Descriptor Framework

> > and Initial object descriptor serves as the starting point of this
framework,
> > why the  "iods" box/atom is not Mandatory in mp4 files?
>
> You can have a MP4 file which is a Sub-part of a presentation. In the 
> "iods" specification (ISO/IEC 144496-14) are some file types case 
> lisetd, with comment if this is a MP4 file or not(free-format).  
> Summary: to have
a
> MP4 Format file there have to be an Object Descriptor.
> You can compare this with the "ctts" box, which is only needed with 
> B-Frames. The "ctts" box is also not mandatory.
>
> > How the Object Descriptor Framework is maintained in case of absence

> > of "iods" box in mp4 file?
>
> A presentation should always be initialized via an IOD, as far as I 
> know.
>
> > Thanks in anticipation
> > Praveen
>
> Regards
> Richard
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