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

[Heiko Purnhagen]

Hi,
> 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.

mp4audec expects files in the MPEG-4 file format (as defined in ISO/IEC
14496-1:2001) ... and this is something completely different from ADTS.
If you want to decode ADTS files, use mp4mcDec instead: it handles
MPEG-2/4 AAC compressed data stored in ADIF, ADTS, raw, or MP4 files.
     Heiko
> 
> 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
> >>
> >>
> >>
> >>
> >
> >
> >
> 
>     ---------------------------------------------------------------
> _______________________________________________
> Mp4-tech mailing list
> Mp4-tech lists.mpegif.org
> http://lists.mpegif.org/mailman/listinfo/mp4-tech