[Mp4-tech][audio] Mpeg4 AAC: why to skip frame

[Shreya Pathak]

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Hi,
  Thanks for the reply.I was testing my Mpeg4 AAC Decoder and 
for PNS test vectors the decoded output length is not same as the reference output.
I am skipping the first two frames of decoder output to match it with the reference waveform.For all other test vectors the output matches, but for PNS test vectors the output length doesnt match.
Please can you suggest me where i am wrong ?
Regards
Shreya
>On Wed, 29 Sep 2023 DDomazet wrote :
> >HI,
> >
> > >Hi,
> > >In Mpeg4 AAC decoder publicly available code from Nero i.e FAAC,
> > >in file decoder.c
> > >if (hDecoder->frame <= 1)
> > >hInfo->samples = 0;
> > >They are skipping the first frame.
> > >I didn't get why they are skipping the first frame.
> >
> >BECAUSE YOU NEED TWO ENCODED FRAMES
> >IN ORDER TO PRODUCE ONE VALID OUTPUT FRAME.
> >
> >FOR DIAGRAMS BELOW:
> >M=1024
> >t - time samples after inverse MDCT transformation
> >f - frequencies after MDCT transformation
> >
> >DECODING:
> >
> >
> >
> >ENCODING:
> >M=1024
> >
> >
> >
> > >Regards
> > >Shreya
> >
> >HOPE THIS HELPS,
> >DANIEL
> >
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