[libav-bugs] [Bug 868] New: AC3 audio gltich : exponent out-of-range

bugzilla at libav.org bugzilla at libav.org
Tue Jun 16 11:59:28 CEST 2015


https://bugzilla.libav.org/show_bug.cgi?id=868

            Bug ID: 868
           Summary: AC3 audio gltich : exponent out-of-range
           Product: Libav
           Version: git HEAD
          Hardware: X86
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: ---
         Component: libavcodec
          Assignee: bugzilla at libav.org
          Reporter: guillaume.marquebielle at parrot.com

Created attachment 544
  --> https://bugzilla.libav.org/attachment.cgi?id=544&action=edit
AC3 sample file with glitches

I'm trying to decode an AC3 file extracted from live French TV stream.
3 audio glitches can be heard in the sample file.

During conversion, error logs are returned.

$ ./avconv -i ./audio_ac3_glitch.ac3 ./output.wav
avconv version v12_dev0-1435-gc0e6b8c, Copyright (c) 2000-2015 the Libav
developers
  built on Jun 12 2015 15:24:09 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
[eac3 @ 0xabf3020] Estimating duration from bitrate, this may be inaccurate
Input #0, eac3, from './audio_ac3_glitch.ac3':
  Duration: 00:00:45.57, start: 0.000000, bitrate: 127 kb/s
    Stream #0:0: Audio: eac3
      48000 Hz, stereo, fltp, 128 kb/s
Output #0, wav, to './output.wav':
  Metadata:
    ISFT            : Lavf56.20.0
    Stream #0:0: Audio: pcm_s16le [[1][0][0][0] / 0x0001]
      48000 Hz, stereo, s16, 1536 kb/s
    Metadata:
      encoder         : Lavc56.26.0 pcm_s16le
Stream mapping:
  Stream #0:0 -> #0:0 (eac3 (native) -> pcm_s16le (native))
Press ctrl-c to stop encoding
[eac3 @ 0xabf4200] exponent out-of-range
[eac3 @ 0xabf4200] error decoding the audio block
[eac3 @ 0xabf4200] exponent out-of-range
[eac3 @ 0xabf4200] error decoding the audio block
[eac3 @ 0xabf4200] exponent out-of-range
[eac3 @ 0xabf4200] error decoding the audio block
[eac3 @ 0xabf4200] incomplete frame
size=    8550kB time=45.57 bitrate=1537.1kbits/s    
video:0kB audio:8550kB other streams:0kB global headers:0kB muxing overhead:
0.000891%


Same errors occur when trying to stream this file using a GSTreamer pipeline :

gst-launch-1.0 -v --gst-debug-level=3 filesrc location=./audio_ac3_glitch.ac3 !
ac3parse ! avdec_eac3 ! audioconvert ! playsink

We can notice that the errors seem related to audio glitches heard.

I've tried to modify the code in file libavcodec/ac3dec.c in function
ac3_decode_frame() where trying to decode the audio blocks generates the log
"error decoding the audio block\n". Without success.

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