[FFmpeg-user] When cutting part of video I get a silence part before it
Toni Cambronero Garcia
tocamgar at gmail.com
Tue Aug 18 00:26:40 EEST 2020
Try to put -ss not before but after the input stream :
ffmpeg -y -i zoom_4.mp4 -ss 61 -to 469 -c copy -async 1 4_compressed.mp4
El sáb., 15 ago. 2020 13:34, Cecil Westerhof <Cecil at decebal.nl> escribió:
> Cecil Westerhof <Cecil at decebal.nl> writes:
>
> Some logging of the problem.
>
> When I use:
> ffmpeg -y -ss 61 -i zoom_4.mp4 -to 469 -acodec copy -vcodec copy
> -async 1 4_compressed.mp4
>
> The video starts with 26 seconds (of negative time stamped) silent
> video.
>
> The log:
> ffmpeg version 4.1.6-1~deb10u1 Copyright (c) 2000-2020 the FFmpeg
> developers
> built with gcc 8 (Debian 8.3.0-6)
> configuration: --prefix=/usr --extra-version='1~deb10u1'
> --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu
> --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl
> --disable-stripping --enable-avresample --disable-filter=resample
> --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom
> --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca
> --enable-libcdio --enable-libcodec2 --enable-libflite
> --enable-libfontconfig --enable-libfreetype --enable-libfribidi
> --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame
> --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt
> --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband
> --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex
> --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab
> --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp
> --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq
> --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opengl
> --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883
> --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
> libavutil 56. 22.100 / 56. 22.100
> libavcodec 58. 35.100 / 58. 35.100
> libavformat 58. 20.100 / 58. 20.100
> libavdevice 58. 5.100 / 58. 5.100
> libavfilter 7. 40.101 / 7. 40.101
> libavresample 4. 0. 0 / 4. 0. 0
> libswscale 5. 3.100 / 5. 3.100
> libswresample 3. 3.100 / 3. 3.100
> libpostproc 55. 3.100 / 55. 3.100
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'zoom_4.mp4':
> Metadata:
> major_brand : mp42
> minor_version : 0
> compatible_brands: isommp42
> creation_time : 2020-07-31T20:26:28.000000Z
> Duration: 00:08:54.24, start: 0.000000, bitrate: 480 kb/s
> Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 32000 Hz,
> mono, fltp, 49 kb/s (default)
> Metadata:
> creation_time : 2020-07-31T20:26:28.000000Z
> handler_name : AAC audio
> Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
> 640x360, 429 kb/s, 25 fps, 25 tbr, 30k tbn, 60k tbc (default)
> Metadata:
> creation_time : 2020-07-31T20:26:28.000000Z
> handler_name : H.264/AVC video
> encoder : AVC Coding
> Output #0, mp4, to '4_compressed.mp4':
> Metadata:
> major_brand : mp42
> minor_version : 0
> compatible_brands: isommp42
> encoder : Lavf58.20.100
> Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
> 640x360, q=2-31, 429 kb/s, 25 fps, 25 tbr, 30k tbn, 30k tbc (default)
> Metadata:
> creation_time : 2020-07-31T20:26:28.000000Z
> handler_name : H.264/AVC video
> encoder : AVC Coding
> Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 32000 Hz,
> mono, fltp, 49 kb/s (default)
> Metadata:
> creation_time : 2020-07-31T20:26:28.000000Z
> handler_name : AAC audio
> Stream mapping:
> Stream #0:1 -> #0:0 (copy)
> Stream #0:0 -> #0:1 (copy)
> Press [q] to stop, [?] for help
> frame=12391 fps=0.0 q=-1.0 Lsize= 29113kB time=00:07:48.98 bitrate=
> 508.5kbits/s speed=1.89e+03x
> video:25861kB audio:2973kB subtitle:0kB other streams:0kB global
> headers:0kB muxing overhead: 0.970170%
>
> What could be the problem?
>
>
> > In the past I had sometimes the following strange problem. When
> > cutting a part out of a video with:
> > ffmpeg -y \
> > -ss "${startSeconds}" \
> > -i "${INPUT_FILE}" \
> > -to "$((stopSeconds - startSeconds))" \
> > -acodec copy \
> > -vcodec copy \
> > -async 1 \
> > "${OUTPUT_FILE}"
> >
> > sometimes before the selected video was put something extra that was
> > silent and had a negative time index.
> >
> > At a certain point I found out that it had to do when compressing the
> > file with:
> > ffmpeg -y \
> > -i "${_inputfile}" \
> > -vcodec libx264 \
> > -crf 23 \
> > -acodec libmp3lame \
> > -preset veryfast \
> > "${_outputfile}"
> >
> > The reason that I did this was that the original file was between four
> > to thirteen times bigger, without me seeing a quality loss.
> > Most of the times I did not have this problem, but sometimes I did.
> > When first cutting the video and then compressing it I did not have
> > this problem.
> >
> > Sadly the problem emerged again. :'-(
> > I have to publish recordings of a Zoom meeting. They are very small
> > (not even 10 MB pro minute) and I got the same problem. I have to
> > generate some logging (I use ffmpeg through bash and tcl scripts), but
> > was wondering if somebody knows what could generate this kind of
> > problems and what to do about it.
> > I will later on share some logging.
>
> --
> Cecil Westerhof
> Senior Software Engineer
> LinkedIn: http://www.linkedin.com/in/cecilwesterhof
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