[FFmpeg-trac] #2497(avcodec:new): ALAC encoder adds a burst of white noise

[FFmpeg]

#2497: ALAC encoder adds a burst of white noise
---------------------------------+--------------------------------------
             Reporter:  pneuman  |                     Type:  defect
               Status:  new      |                 Priority:  normal
            Component:  avcodec  |                  Version:  git-master
             Keywords:  alac     |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
---------------------------------+--------------------------------------
 Hi,

 I have a particular WAV file that, when converted to ALAC, contains a
 short burst of noise not present in the original WAV. This is clearly
 audible, and also clearly visible when comparing the original WAV to the
 ALAC in a tool like Audacity. The burst of noise is between the 1:14 and
 1:15 mark.

 I've reproduced this using ffmpeg from git compiled earlier today. The
 command line was as follows:

 ffmpeg -y -i alac_encoding_error_white_noise_burst.wav -acodec alac -f
 ipod out.m4a

 Output was as follows:

 {{{
 ffmpeg version N-52419-gdfdee6c Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Apr 24 2013 09:52:56 with gcc 4.7 (Ubuntu/Linaro
 4.7.2-2ubuntu1)
   configuration:
   libavutil      52. 27.100 / 52. 27.100
   libavcodec     55.  6.100 / 55.  6.100
   libavformat    55.  3.100 / 55.  3.100
   libavdevice    55.  0.100 / 55.  0.100
   libavfilter     3. 60.101 /  3. 60.101
   libswscale      2.  2.100 /  2.  2.100
   libswresample   0. 17.102 /  0. 17.102
 [wav @ 0x27b07c0] max_analyze_duration 5000000 reached at 5015510
 microseconds
 Guessed Channel Layout for  Input Stream #0.0 : stereo
 Input #0, wav, from 'alac_encoding_error_white_noise_burst.wav':
   Duration: 00:05:46.91, bitrate: 1411 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz,
 stereo, s16, 1411 kb/s
 Output #0, ipod, to 'out.m4a':
   Metadata:
     encoder         : Lavf55.3.100
     Stream #0:0: Audio: alac (alac / 0x63616C61), 44100 Hz, stereo, s16p,
 128 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le -> alac)
 Press [q] to stop, [?] for help
 size=   51784kB time=00:05:46.99 bitrate=1222.5kbits/s
 video:0kB audio:51768kB subtitle:0 global headers:0kB muxing overhead
 0.030579%
 }}}

 I can supply the WAV file, but it's copyright belongs to the user that
 uploaded it to our service, so I wouldn't feel comfortable uploading it to
 datafilehost.com unless I can supply the link to the relevant developer
 privately.

 I did try to upload it to the FTP server, but had no luck there (there was
 no "incoming" directory, and I got a permission denied error trying to
 upload to the root directory).

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2497>
FFmpeg <http://ffmpeg.org>
FFmpeg issue tracker