Loop the first frame of a video and then play a selected portion of the video

Question

I would like to to play the first frame of an input video for 260 frames and then play frames 310–930 of the input video:

$ ffmpeg -i video.mp4 -i video.mp4 -filter_complex '
    [0:v]loop=loop=259:size=1:start=0[first-frame];
    [1:v]trim=start_frame=310:end_frame=930,setpts=PTS-STARTPTS[rest];
    [first-frame][rest]concat=n=2:v=1:a=0[output]
' -map [output] -c:v libx264 -crf 18 -y output.mp4

The above command produces the first frame of the input video for 260 frames as expected, but then continues with frames 0-620 of the input video followed by frames 310–930 of the input video.

When I drop the [first-frame] part, frames 310–930 of the input video are correctly produced:

$ ffmpeg -i video.mp4 -i video.mp4 -filter_complex '
    [1:v]trim=start_frame=310:end_frame=930,setpts=PTS-STARTPTS[rest];
    [rest]concat=n=1:v=1:a=0[output]
' -map [output] -c:v libx264 -crf 18 -y output.mp4

This is perhaps a timestamp problem, since the documentation for the concat filter clarifies that “for this filter to work correctly, all segments must start at timestamp 0.”

I am using the following version of ffmpeg:

$ ffmpeg -version
ffmpeg version 3.2.12-1~deb9u1 Copyright (c) 2000-2018 the FFmpeg developers
built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
libavutil      55. 34.101 / 55. 34.101
libavcodec     57. 64.101 / 57. 64.101
libavformat    57. 56.101 / 57. 56.101
libavdevice    57.  1.100 / 57.  1.100
libavfilter     6. 65.100 /  6. 65.100
libavresample   3.  1.  0 /  3.  1.  0
libswscale      4.  2.100 /  4.  2.100
libswresample   2.  3.100 /  2.  3.100
libpostproc    54.  1.100 / 54.  1.100

Answer 1

A shorter method is

ffmpeg -i video.mp4 -vf 'select=eq(n,0)+between(n,310,930),setpts=if(eq(N,0),0,(N+260)/FRAME_RATE/TB)' -map [output] -vsync cfr -c:v libx264 -crf 18 -y output.mp4

Answer 2

The loop filter produces the rest of the video after it has stopped looping. If this is undesirable, trim the resulting video as follows:

$ ffmpeg -i video.mp4 -i video.mp4 -filter_complex '
    [0:v]loop=loop=259:size=1:start=0,trim=start_frame=0:end_frame=259[first-frame];
    [1:v]trim=start_frame=310:end_frame=930,setpts=PTS-STARTPTS[rest];
    [first-frame][rest]concat=n=2:v=1:a=0[output]
' -map [output] -c:v libx264 -crf 18 -y output.mp4

This behavior is perhaps counterintuitive and poorly documented, but it covers the common case, when one wants to loop at the beginning of a video. This behavior also makes loop=0 an identity filter that passes the video unchanged.