[FFmpeg-trac] #2484(avfilter:new): atempo - low accuracy
FFmpeg
trac at avcodec.org
Fri Apr 19 17:49:34 CEST 2013
#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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