[FFmpeg-trac] #4696(ffmpeg:new): Duration with -t before -i is actually value of -t plus value of -ss

[FFmpeg]

#4696: Duration with -t before -i is actually value of -t plus value of -ss
---------------------------------+----------------------------------
             Reporter:  Piscium  |                     Type:  defect
               Status:  new      |                 Priority:  normal
            Component:  ffmpeg   |                  Version:  2.4.10
             Keywords:           |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
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 If I run the command below I would expect the duration of the output file
 to be 30 seconds, but instead it is 40.

 ffmpeg  -y -ss 10 -t 30 -i in.m4a -acodec copy -flags global_header
 out.m4a

 It seems this is a bug. It may be the same bug or related to bug #4475.

 In case somebody else comes across this bug, the workaround is to subtract
 the value of the -ss parameter from the value of the -t parameter, as
 follows:

 ffmpeg  -y -ss 10 -t 20 -i in.m4a -acodec copy -flags global_header
 out.m4a

 With the above I get the intended duration of 30 seconds.

 Note that if the duration is less than the seek point you need to enter a
 negative duration for the workaround, for example the command below will
 also give me the desired duration of 30 seconds.

 ffmpeg -y -ss 92 -t -62 -i in.m4a  -acodec copy -flags global_header
 out.m4a

 ----------------------------------
 ffmpeg -version
 ffmpeg: /usr/lib64/nvidia-304xx/libOpenCL.so.1: no version information
 available (required by ffmpeg)
 ffmpeg: /usr/lib64/nvidia-304xx/libOpenCL.so.1: no version information
 available (required by /lib64/libavfilter.so.5)
 ffmpeg: /usr/lib64/nvidia-304xx/libOpenCL.so.1: no version information
 available (required by /lib64/libavutil.so.54)
 ffmpeg version 2.4.10 Copyright (c) 2000-2015 the FFmpeg developers
 built on Jun  3 2015 08:36:36 with gcc 4.9.2 (GCC) 20150212 (Red Hat
 4.9.2-6)
 configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg
 --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man
 --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Werror=format-security
 -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-
 buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' --enable-bzlib
 --disable-crystalhd --enable-frei0r --enable-gnutls --enable-ladspa
 --enable-libass --enable-libcdio --enable-libdc1394 --disable-indev=jack
 --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-openal
 --enable-opencl --enable-libopencv --enable-libopenjpeg --enable-libopus
 --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-
 libspeex --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-
 libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-x11grab
 --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads
 --disable-static --enable-shared --enable-gpl --disable-debug --disable-
 stripping --shlibdir=/usr/lib64 --enable-runtime-cpudetect
 libavutil      54.  7.100 / 54.  7.100
 libavcodec     56.  1.100 / 56.  1.100
 libavformat    56.  4.101 / 56.  4.101
 libavdevice    56.  0.100 / 56.  0.100
 libavfilter     5.  1.100 /  5.  1.100
 libavresample   2.  1.  0 /  2.  1.  0
 libswscale      3.  0.100 /  3.  0.100
 libswresample   1.  1.100 /  1.  1.100
 libpostproc    53.  0.100 / 53.  0.100

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Ticket URL: <https://trac.ffmpeg.org/ticket/4696>
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