[FFmpeg-trac] #6035(undetermined:new): wmavoice: files decodes incorrectly

FFmpeg trac at avcodec.org
Thu Dec 22 17:38:46 EET 2016

#6035: wmavoice: files decodes incorrectly
             Reporter:  ami_stuff    |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0

Comment (by rbultje):

 I looked at the 8khz 8kbps sample in a some detail. There is indeed a
 tonal problem. At the point where this starts, we're mostly coding
 fb_idx=11, so acb_type=hamming with 4 blocks/frame and 0 double pulses.

 The source of the problem appears to start in the "excitation" array as
 written in line 1398 (call to ff_acelp_interpolatef()). What happens is
 that the values in that array build up to be insanely large over time,
 starting at the point where the tone starts going off (4.9s into the
 file). fcb_gain/acb_gain appear fine in that section of the code. The
 block pitch also seems sensible (low to mid-40s). Since the code simply
 interpolates excitation energy from history without any further input, it
 seems almost like a buildup of error through the filter history. I'll have
 to go through the original code to see whether it deals with this in some
 way or whether there's some slight problem in how the filter coefficients
 were generated or something like that...

 So in short, I'm not 100% sure what's going on here.

Ticket URL: <https://trac.ffmpeg.org/ticket/6035#comment:1>
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