[FFmpeg-user] Concat Creates SlowMo Audio for a Portion of Output

[Paul B Mahol]

On Fri, Apr 14, 2023 at 2:21 PM ace8cjc via ffmpeg-user <
ffmpeg-user at ffmpeg.org> wrote:

> Hi, I have two clips that I am trying to concat.
>
> clip1.dv (raw .dv stream captured via ffmpeg).
> clip2.dv (raw .dv stream captured via ffmpeg, trimmed slightly in iMovie
> HD6, and then exported in fully quality).
>
> When I use ffmpeg to concat the two clips, the output.dv plays back the
> clip2 portion with super slow-mo audio. The audio of clip1 and the video of
> both clips plays back fine.
>
> The video source of the two clips is the exact same, and so I know the
> issue stems from the export of clip2 in iMovie HD6. But, iMovie HD6
> handles .dv files natively and the export to full quality should keeps the
> original codecs.
>
> I understand iMovie HD6 is 3rd party, and so am not asking for help with
> his software. But, any ideas on how to normalize the audio of clip2 during
> the concat using ffmpeg?
>
> Here is command-line:
>
> ffmpeg -f concat -i mylist.txt -map 0:0 -c copy output.dv
> ffmpeg version 5.1.2 Copyright (c) 2000-2022 the FFmpeg developers
>   built with Apple clang version 14.0.0 (clang-1400.0.29.202)
>   configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.2_6 --enable-shared
> --enable-pthreads --enable-version3 --cc=clang --host-cflags=
> --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl
> --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d
> --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist
> --enable-librubberband --enable-libsnappy --enable-libsrt
> --enable-libsvtav1 --enable-libtesseract --enable-libtheora
> --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx
> --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
> --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype
> --enable-frei0r --enable-libass --enable-libopencore-amrnb
> --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex
> --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack
> --disable-indev=jack --enable-videotoolbox
>   libavutil      57. 28.100 / 57. 28.100
>   libavcodec     59. 37.100 / 59. 37.100
>   libavformat    59. 27.100 / 59. 27.100
>   libavdevice    59.  7.100 / 59.  7.100
>   libavfilter     8. 44.100 /  8. 44.100
>   libswscale      6.  7.100 /  6.  7.100
>   libswresample   4.  7.100 /  4.  7.100
>   libpostproc    56.  6.100 / 56.  6.100
> [dv @ 0x7fa07d904dc0] Detected timecode is invalid
> [dv @ 0x7fa07d904dc0] Estimating duration from bitrate, this may be
> inaccurate
> Input #0, concat, from 'mylist.txt':
>   Duration: N/A, start: 0.000000, bitrate: 27048 kb/s
>   Stream #0:0: Video: dvvideo, yuv411p, 720x480 [SAR 8:9 DAR 4:3], 25000
> kb/s, 29.97 fps, 29.97 tbr, 29.97 tbn
>   Stream #0:1: Audio: pcm_s16le, 32000 Hz, stereo, s16, 1024 kb/s
>   Stream #0:2: Audio: pcm_s16le, 32000 Hz, stereo, s16, 1024 kb/s
> Output #0, dv, to 'output.dv':
>   Metadata:
>     encoder         : Lavf59.27.100
>   Stream #0:0: Video: dvvideo, yuv411p, 720x480 [SAR 8:9 DAR 4:3], q=2-31,
> 25000 kb/s, 29.97 fps, 29.97 tbr, 29.97 tbn
> Stream mapping:
>   Stream #0:0 -> #0:0 (copy)
> Press [q] to stop, [?] for help
> [dv @ 0x7fa07d904dc0] Detected timecode is invalid00:58:50.66
> bitrate=28770.8kbits/s speed= 243x
> [dv @ 0x7fa07d904dc0] Estimating duration from bitrate, this may be
> inaccurate
> frame=110448 fps=7265 q=-1.0 Lsize=12943125kB time=01:01:25.28
> bitrate=28771.2kbits/s speed= 242x
> video:12943125kB audio:0kB subtitle:0kB other streams:0kB global
> headers:0kB muxing overhead: 0.000000%
>

Make sure that all inputs have exactly same audio sample rate.


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