[FFmpeg-trac] #2484(avfilter:new): atempo - low accuracy

[FFmpeg]

#2484: atempo - low accuracy
------------------------------------+------------------------------------
             Reporter:  bars        |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:  atempo      |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+------------------------------------
Changes (by cehoyos):

 * keywords:   => atempo
 * version:  unspecified => git-master
 * component:  FFmpeg => avfilter


Comment:

 I tested the following - could you confirm if this is the problem you are
 seeing?
 Encoding 24000 seconds (6:40:00) of audio with 48kHz:
 {{{
 $ ffmpeg -f lavfi -i "aevalsrc=sin(2*PI*t*440):d=24000:s=48k" out24000.wav
 ffmpeg version N-52268-g42bcc40 Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Apr 19 2013 17:40:42 with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl --disable-indev=jack
   libavutil      52. 27.100 / 52. 27.100
   libavcodec     55.  4.100 / 55.  4.100
   libavformat    55.  3.100 / 55.  3.100
   libavdevice    55.  0.100 / 55.  0.100
   libavfilter     3. 58.100 /  3. 58.100
   libswscale      2.  2.100 /  2.  2.100
   libswresample   0. 17.102 /  0. 17.102
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, lavfi, from 'aevalsrc=sin(2*PI*t*440):d=24000:s=48k':
   Duration: N/A, start: 0.000000, bitrate: 3072 kb/s
     Stream #0:0: Audio: pcm_f64le, 48000 Hz, mono, dbl, 3072 kb/s
 Output #0, wav, to 'out24000.wav':
   Metadata:
     ISFT            : Lavf55.3.100
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, mono,
 s16, 768 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_f64le -> pcm_s16le)
 Press [q] to stop, [?] for help
 size= 2250000kB time=06:40:00.00 bitrate= 768.0kbits/s
 video:0kB audio:2250000kB subtitle:0 global headers:0kB muxing overhead
 0.000003%
 }}}
 Slowing audio down as proposed by you (6:57:05), the output size is ~1.5
 seconds off for seven hours, indicating noticeable A/V desync for a two-
 hour movie (iiuc):
 {{{
 $ ffmpeg -i out24000.wav -af "atempo=24000/25025" out25025.wav
 ffmpeg version N-52268-g42bcc40 Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Apr 19 2013 17:40:42 with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl --disable-indev=jack
   libavutil      52. 27.100 / 52. 27.100
   libavcodec     55.  4.100 / 55.  4.100
   libavformat    55.  3.100 / 55.  3.100
   libavdevice    55.  0.100 / 55.  0.100
   libavfilter     3. 58.100 /  3. 58.100
   libswscale      2.  2.100 /  2.  2.100
   libswresample   0. 17.102 /  0. 17.102
   libpostproc    52.  3.100 / 52.  3.100
 [wav @ 0x288a780] max_analyze_duration 5000000 reached at 5034667
 microseconds
 Guessed Channel Layout for  Input Stream #0.0 : mono
 Input #0, wav, from 'out24000.wav':
   Metadata:
     encoder         : Lavf55.3.100
   Duration: 06:40:00.00, bitrate: 768 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, mono,
 s16, 768 kb/s
 Output #0, wav, to 'out25025.wav':
   Metadata:
     ISFT            : Lavf55.3.100
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, mono,
 s16, 768 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
 Press [q] to stop, [?] for help
 size= 2346232kB time=06:57:06.47 bitrate= 768.0kbits/s
 video:0kB audio:2346232kB subtitle:0 global headers:0kB muxing overhead
 0.000003%
 }}}

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2484#comment:1>
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