[FFmpeg-trac] #7288(avfilter:new): The amix filter is truncating a channel on merge
FFmpeg
trac at avcodec.org
Fri Jun 29 13:00:29 EEST 2018
#7288: The amix filter is truncating a channel on merge
-------------------------------------+-------------------------------------
Reporter: veryflatcat | Type: defect
Status: new | Priority: normal
Component: avfilter | Version:
Keywords: | unspecified
Blocking: | Blocked By:
Analyzed by developer: 0 | Reproduced by developer: 0
-------------------------------------+-------------------------------------
Summary of the bug:
When merging 3 opus encoded audio channels in a mkv formatted container,
the primary issue is that the first channel is incorrectly truncated. As a
separate issue, the 3rd channel is incorrectly positioned in time.
We have the following from ffprobe of the input file:
{{{
Stream #0:0: Audio: opus, 48000 Hz, mono, fltp (default)
Metadata:
DURATION : 00:00:02.023000000
Stream #0:1: Audio: opus, 48000 Hz, mono, fltp (default)
Metadata:
DURATION : 00:00:02.048000000
Stream #0:2: Audio: opus, 48000 Hz, mono, fltp (default)
Metadata:
DURATION : 00:00:02.038000000
}}}
* Stream #0.0 is 2 seconds long, starts at 0 seconds and contains a 1kHz
sine wave that was opus encoded
* Stream #0.1 is 2 seconds long, starts at 0 seconds and contains a 1.5kHz
sine wave that was opus encoded
* Strea2 #0.2 is 1 second long, with the first packet apearing at 1 second
and contains a 2kHz sine wave that was opus encoded
How to reproduce:
The ffmpeg version is 4.0.1-0york0~16.04 (Ubuntu)
{{{
ffmpeg --i test.mkv -filter_complex amix=inputs=3:duration=longest -ar
8000 test.wav
}}}
This produces the expected wav file with the input stream #0:0 truncated
at 1 second. The stream #0:2 starts at 0 seconds even though the first
packet appears 1 second into the mkv stream.
This can be established by viewing a spectrogram of test.wav (Audacity has
such a tool). Attached is the input file (test.mkv) as well as an
annotated output from Audacity's spectrogram view.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/7288>
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