Looping a section of a video can be useful for presentations or advanced video editing. In this example the input.mp4 is a 5 minute long video with the requirement that after the 1 minute mark, the video will loop 10 times.
$ ffmpeg -i input.mp4 -filter_complex "loop=loop=10:size=1500:start=1500" -pix_fmt yuv420p output.mp4
In the requirements for this example, it was stated after the 1 minute mark the video will loop yet the start number is 1500. This is because start requires a frame value not time. To calculate the frame value one must know the framerate of the input. In this example, input.mp4 has a 30 frames per second framerate (FPS). 30 FPS * 1 minute (60 seconds) = 1500 frames.
In addition to the start parameter, a size parameter must be set as well. size is the number of frames that are repeated. So from frames 0 to 1500 the loop will play 10 times after the 1500th frame has been played.
loop Indicates the name of the loop filter loop Indicates the number of loops (default is 0 with -1 being infinite) size Indicates the number of frames (from 0 to value) that are repeated start Indicates first or starting frame of the loop (default is 0)
The loop filter works great with video but does not apply to audio output. Thus another method is required. Using concat multiple times on the same file could be used instead:
$ ffmpeg -i input.mp4 -i input.mp4 -i input.mp4 -filter_complex "concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4
Then with the use of seeking, -ss, the section to be repeated can be specified.
Challenge: Try looping a specific section of a video using concat.
Below is the command to identify the frame rate of an input file, this one has a frame rate of 29.97:
$ ffmpeg -i input.mp4 ffmpeg version 4.2.2 Copyright (c) 2000-2019 the FFmpeg developers built with Apple clang version 11.0.0 (clang-1220.127.116.11) Configuration: <removed for clarity> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4': Metadata: major_brand : isom minor_version : 512 compatible_brands: isomiso2avc1mp41 encoder : Lavf58.29.100 Duration: 00:00:20.05, start: 0.000000, bitrate: 1802 kb/s Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x480 [SAR 40:33 DAR 20:11], 1667 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default) Metadata: handler_name : Core Media Video timecode : 01:00:00:00 Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default) Metadata: handler_name : Core Media Audio Stream #0:2(eng): Data: none (tmcd / 0x64636D74), 0 kb/s Metadata: handler_name : Core Media Video timecode : 01:00:00:00