FFMPEG fails to trim beginning of clip

Question

I have two .MTS files taken in sequence and I want to trim them to the first five seconds. This command works for the first file:

ffmpeg -ss 0 -to 5 -i 00117.MTS -vcodec copy -acodec copy start_00117.MTS

The result is 5 seconds and 17 MB, as opposed to the 12 minutes and 2 GB from the original.

The same command on the second file fails:

ffmpeg -ss 0 -to 5 -i 00118.MTS -vcodec copy -acodec copy start_00118.MTS

The result is 12 minutes and 2 GB, like its original file.

What is the problem?

Full log :

$ rm start_00117.MTS; ffmpeg -ss 0 -to 5 -i 00117.MTS -vcodec copy -acodec copy start_00117.MTS
ffmpeg version 4.1.4 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple LLVM version 10.0.1 (clang-1001.0.46.4)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1.4_1 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-12.0.1.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-12.0.1.jdk/Contents/Home/include/darwin' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-videotoolbox --disable-libjack --disable-indev=jack --enable-libaom --enable-libsoxr
  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, mpegts, from '00117.MTS':
  Duration: 00:12:36.02, start: 1.040000, bitrate: 22490 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 256 kb/s
    Stream #0:2[0x1200]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090), 1920x1080
Output #0, mpegts, to 'start_00117.MTS':
  Metadata:
    encoder         : Lavf58.20.100
    Stream #0:0: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(top first), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 25 fps, 50 tbr, 90k tbn, 90k tbc
    Stream #0:1: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 256 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame=  304 fps=0.0 q=-1.0 Lsize=   16601kB time=00:00:06.02 bitrate=22590.4kbits/s speed=25.8x    
video:15162kB audio:189kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 8.143849%
$ rm start_00118.MTS; ffmpeg -ss 0 -to 5 -i 00118.MTS -vcodec copy -acodec copy start_00118.MTS
rm: start_00118.MTS: No such file or directory
ffmpeg version 4.1.4 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple LLVM version 10.0.1 (clang-1001.0.46.4)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1.4_1 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-12.0.1.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-12.0.1.jdk/Contents/Home/include/darwin' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-videotoolbox --disable-libjack --disable-indev=jack --enable-libaom --enable-libsoxr
  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, mpegts, from '00118.MTS':
  Duration: 00:12:36.59, start: 756.592000, bitrate: 22471 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 256 kb/s
    Stream #0:2[0x1200]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090), 1920x1080
Output #0, mpegts, to 'start_00118.MTS':
  Metadata:
    encoder         : Lavf58.20.100
    Stream #0:0: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(top first), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 25 fps, 50 tbr, 90k tbn, 90k tbc
    Stream #0:1: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 256 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame=37804 fps=923 q=-1.0 Lsize= 2130467kB time=00:12:36.54 bitrate=23069.0kbits/s speed=18.5x    
video:1946718kB audio:23627kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 8.126621%

Answer 1

This looks to be a bug with input -to . For now, use -ss and -to as output options.

ffmpeg -i 00118.MTS -ss 0 -to 5 -c copy start_00118.MTS

Answer 2

Using -c copy may fail in several situations and this is one of them. From the documentation :

Stream copy is a mode selected by supplying the copy parameter to the -codec option. It makes ffmpeg omit the decoding and encoding step for the specified stream, so it does only demuxing and muxing. It is useful for changing the container format or modifying container-level metadata. The diagram above will, in this case, simplify to this:

 _______ ______________ ________ | | | | | | | input | demuxer | encoded data | muxer | output | | file | ---------> | packets | -------> | file | |_______| |______________| |________|

Since there is no decoding or encoding, it is very fast and there is no quality loss. However, it might not work in some cases because of many factors.

This is one such factor. See the closed bug report for a longer explanation and the coincidence of why the command works with the first section of a long record and not the second section.

Removing -c copy (or -vcodec copy -acodec copy ) fixes the corner case, ie:

ffmpeg -ss 0 -to 5 -i 00122.MTS start_00122.MTS

See also Gyan's solution of using -ss and -to as output options, which also fixes the corner case.