[Mp4-tech] Decoding an MPEG-2 AAC stream : Help

[sunx]

I never tried the MPEG2-ADTS streams. Here is my suggestion:
Open the Microsoft VC++. Drag the bitstream into VC++. If you can find
some readable four byte combinations, e.g., "ftyp", "uuid", "mp4v",
"mp4a", "mdat", etc, then this is MPEG-4 System file. You can download the
"mpeg4ip" software, in which there is a MPEG-4 Demux. Otherwise, it is
nother media format, maybe MPEG-4 AAC, or MPEG-2 audio. You need to check
the spec. and bit syntax very carefully.
On Wed, 12 Nov 2003, ramesh raman wrote:
> Hi,
> Thanks for the quick response.  But i dont understand.
> My  problem is i have  an MPEG2-ADTS stream. It is an AAC stream. I want
> to decode this using the MPEG-4.
>
> Also, i get the same error, when i use other MPEG2-AAC streams (from the
> MPEG-2 conformance CD ). I tried to decode the L7....aac and M6_48k.aac
>  test vectors belonging to the Low complexity and main profiles
> respectively.
>
> I wonder if the MPEG-4 Decoder looks for some particular header ? is
> this what you meant by the system file ?
> Is it that i need to put this "raw" MPEG-2 stream into  another stream
> with a "Mpeg-4 system" header ?
> If so, where do i get the format of that system header from ?  Is there
> already any program to do that encapsulation that comes with the
> reference s/w ?
>
> Thanks in advance
> regards
> /ramesh
>
>
> sunx wrote:
>
> >The .mp4 should be MPEG-4 System file. You need a MPEG-4 Demux to extract
> >the AAC stream first.
> >
> >On Wed, 12 Nov 2003, ramesh raman wrote:
> >
> >
> >
> >>  Hi all,
> >>
> >>I am new to MPEG-4.  I downloaded the public distribution code and i
> >>have compiled the MPEG-4 Decoder code on Linux.
> >>I try to run it with the following options :
> >>
> >>./mp4audec test.mp4 -o test.raw
> >>                                           test.mp4 is an MPEG-2 AAC
> >>ADTS stream (which decodes correctly on a MPEG-2 AAC decoder) present in
> >>local dir.
> >>
> >>When i run  the program, i get the following error,
> >>mp4audec: WARNING: error decoding audio file test.mp4
> >>
> >>Could anybody please tell me what options i need to set to decode an
> >>MPEG-2 AAC Encoded stream.
> >>
> >>Now, here are few things i observed while trying to step through:
> >>
> >>1. While stepping through the function  "MP4ParseAtomUsingProtoList"
> >> in the libisomedia.a library, there is a comparison of the FIRST 4
> >>Bytes read from the stream with the File size.  (In file MP4atoms.c   :
> >> exact code is as below :
> >>    err = MP4CreateBaseAtom( atomProto ); if ( err ) goto bail;
> >>
> >>    /* atom size */
> >>    err = inputStream->read32( inputStream, &atomProto->size, NULL ); if
> >>( err ) goto bail;
> >>    if ( atomProto->size == 0 )
> >>        BAILWITHERROR( MP4NoQTAtomErr )
> >>    if ( (atomProto->size < 0) || ((atomProto->size - 4) >
> >>inputStream->available) )
> >>        BAILWITHERROR( MP4BadDataErr )
> >>
> >>the atomProto->size in my case become 0xfff94d80    and this check fails
> >>here  )
> >>
> >>2. The .mp4 file that i have doesnt contain the file size in the first 4
> >>bytes (It actually contains  0xff 0xf9 0x4D 0x80 , while the file size
> >>in hex is  0xB637CB bytes)
> >>
> >>Can anybody please tell me if i need to give any specific options to the
> >>MPEG4 decoder , so that it can decode this stream.
> >>I apologize if my question has already been answered earlier.
> >>
> >>thanks in advance
> >>regards
> >>/ramesh
> >>
> >>
> >>
> >>
> >
> >
> >
> >
>
>