Mark Taylor schrieb am Mon, 03 Jul 2000:
> >
> >
> > Thanks Mathew, I just changed VbrTag.c to set
> > the CRC bit for the Xing-VBR tagging frame
> > like the first frame.
> >
> > Now mpg123 works with protected VBR files.
> >
> >
> > Robert
> >
>
> This is probabaly the right thing to do, but:
>
> Now, the Xing VBR header is actually a corrupt
> mp3 frame. Before this fix, the Xing header was a valid mp3
> frame which would decode to silence.
>
> So mpg123 now works, but there might be another decoder,
> which is not VBR aware (like mpg123) but does actually check
> the CRC (unlike mpg123). This decoder may now choke
> on the mp3 file because the first frame is corrupt?
>
>
> Mark
OK, here is the statement out of
"MPEG Layer3 / Bitstream Syntax and Decoding"
<quote>
If the words (CRC checksum and transmitted values) are not
identical, a transmission error has occured in the protected
field of the bitstream. To avoid annoying distortions,
application of a concealment technique, such as muting of the
actual audio frame or repetition of the previous audio frame,
is recommended.
</quote>
From my point of view a repetition should not be choosen for
the very first frame like the Xing-VBR tagging frame.
Robert
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