[Mp4-tech] Question about mismatch between faad output and reference wave.

[Menno Bakker]

Hi,
Yes, you're doing something wrong. You either forgot to compensate for
the different decoder delay (2048 samples) or your code to get
"sample" is wrong.
Menno
On Fri, 22 Oct 2023 11:28:41 +0800, Zhang, Ying S
<ying.s.zhang intel.com> wrote:
>  
>  
> 
> I use "faad.exe -b 2 -o outfilename infilename" to generate some 24bit pcm
> wave file. 
> 
> The output wave files seem quite different with reference stream. 
> 
> The maximum absolute value is much higher than 2-14 relative to full scale. 
> 
> I don't know what's wrong with that. The audio signal sounds alike. 
> 
> I calculate the each sample doing: 
> 
> " 
> 
> Sample = ((*(mmioinfoRef.pchNext+2))<<16)&0xFF0000 +
> (((*(mmioinfoRef.pchNext+1))<<8)&0xFF00)+(*mmioinfoRef.pchNext&0xFF); 
> 
> if(Sample>>23 ==1)  Sample |= 0xFF000000; 
> 
> " 
> 
> Do I use the wrong configuration in faad.exe or do I calculate the sample
> value wrong? 
> 
> Or the difference is reasonable? 
> 
> For example, I use al_sbr_s_32_1.mp4 as input and the maximum absolute value
> is 2492181 while RMS is about 41.5 which is acceptable. 
> 
>   
> 
> Can any one give some hint? 
> 
>   
> 
> Thanks! 
> 
>   
> 
> Best Regards, 
> 
>   
> 
>  
> Zhang Ying  
> 
> iNet: 8-752-1572 
> 
> Tel:  +86-21-52574545-1572 
> 
>   
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