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When I use ffmpeg to go from a video to frames, and then back to video, the duration is different between the videos
24 February 2024, by bluepandaI am trying to use
ffmpeg
to convert from a .mp4 (or .mov) video into individual frames, do some processing on those frames, and then convert back to .mp4. The problem is that the resulting video I create is a different duration than the input - I can see this visually when I play the two videos side by side. The difference is not large (i.e.00:00:00.50
for the input video and00:00:00.52
for the output video), but when the videos are looped next to each other they get out of sync.

Here is information about the input video retrieved using
fluent-ffmpeg
'sffmpeg.ffprobe(videoPath)
:

metadata {
 streams: [
 {
 index: 0,
 codec_name: 'h264',
 codec_long_name: 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10',
 profile: 'High',
 codec_type: 'video',
 codec_tag_string: 'avc1',
 codec_tag: '0x31637661',
 width: 1080,
 height: 1920,
 coded_width: 1080,
 coded_height: 1920,
 closed_captions: 0,
 has_b_frames: 2,
 sample_aspect_ratio: 'N/A',
 display_aspect_ratio: 'N/A',
 pix_fmt: 'yuv420p',
 level: 40,
 color_range: 'tv',
 color_space: 'bt709',
 color_transfer: 'bt709',
 color_primaries: 'bt709',
 chroma_location: 'left',
 field_order: 'unknown',
 refs: 1,
 is_avc: 'true',
 nal_length_size: 4,
 id: 'N/A',
 r_frame_rate: '30000/1001',
 avg_frame_rate: '27000/1001',
 time_base: '1/30000',
 start_pts: 0,
 start_time: 0,
 duration_ts: 15100,
 duration: 0.503333,
 bit_rate: 5660223,
 max_bit_rate: 'N/A',
 bits_per_raw_sample: 8,
 nb_frames: 36,
 nb_read_frames: 'N/A',
 nb_read_packets: 'N/A',
 tags: [Object],
 disposition: [Object]
 },
 {
 index: 1,
 codec_name: 'aac',
 codec_long_name: 'AAC (Advanced Audio Coding)',
 profile: 'LC',
 codec_type: 'audio',
 codec_tag_string: 'mp4a',
 codec_tag: '0x6134706d',
 sample_fmt: 'fltp',
 sample_rate: 48000,
 channels: 2,
 channel_layout: 'stereo',
 bits_per_sample: 0,
 id: 'N/A',
 r_frame_rate: '0/0',
 avg_frame_rate: '0/0',
 time_base: '1/48000',
 start_pts: 0,
 start_time: 0,
 duration_ts: 24160,
 duration: 0.503333,
 bit_rate: 248416,
 max_bit_rate: 'N/A',
 bits_per_raw_sample: 'N/A',
 nb_frames: 27,
 nb_read_frames: 'N/A',
 nb_read_packets: 'N/A',
 tags: [Object],
 disposition: [Object]
 }
 ],
 format: {
 filename: '/Users/name/images/input.mp4',
 nb_streams: 2,
 nb_programs: 0,
 format_name: 'mov,mp4,m4a,3gp,3g2,mj2',
 format_long_name: 'QuickTime / MOV',
 start_time: 0,
 duration: 0.503333,
 size: 963879,
 bit_rate: 15319941,
 probe_score: 100,
 tags: {
 major_brand: 'mp42',
 minor_version: '1',
 compatible_brands: 'isommp41mp42',
 creation_time: '2024-02-14T01:21:12.000000Z'
 }
 },
 chapters: []
}



and here is from running
ffprobe
directly:

ffprobe '/Users/name/images/input.mp4'
ffprobe version 6.1.1 Copyright (c) 2007-2023 the FFmpeg developers
 built with Apple clang version 15.0.0 (clang-1500.1.0.2.5)
 configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/6.1.1_2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopenvino --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
 libavutil 58. 29.100 / 58. 29.100
 libavcodec 60. 31.102 / 60. 31.102
 libavformat 60. 16.100 / 60. 16.100
 libavdevice 60. 3.100 / 60. 3.100
 libavfilter 9. 12.100 / 9. 12.100
 libswscale 7. 5.100 / 7. 5.100
 libswresample 4. 12.100 / 4. 12.100
 libpostproc 57. 3.100 / 57. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/name/images/input.mp4':
 Metadata:
 major_brand : mp42
 minor_version : 1
 compatible_brands: isommp41mp42
 creation_time : 2024-02-14T01:21:12.000000Z
 Duration: 00:00:00.50, start: 0.000000, bitrate: 15319 kb/s
 Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1080x1920, 5660 kb/s, 26.97 fps, 29.97 tbr, 30k tbn (default)
 Metadata:
 creation_time : 2024-02-14T01:21:12.000000Z
 handler_name : Core Media Video
 vendor_id : [0][0][0][0]
 encoder : AVC Coding
 Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 248 kb/s (default)
 Metadata:
 creation_time : 2024-02-14T01:21:12.000000Z
 handler_name : Core Media Audio
 vendor_id : [0][0][0][0]



And this is my command to go from video to frames:


ffmpeg -i /Users/name/images/input.mp4 -y -f image2 /Users/name/images/frames/%d.png



After which I convert the frames back to video with this - note that I get by seeing
avg_frame_rate
is27000/1001 = 26.97302697
:

ffmpeg -r 26.973026973026972 -i /Users/name/images/frames/%d.png -y -r 26.973026973026972 -b:v 5660223k -f mp4 -pix_fmt yuv420p -t 0.503333 /Users/name/images/output.mp4



And if I then run
fluent-ffmpeg
'sffmpeg.ffprobe(videoPath)
I get:

metadata {
 streams: [
 {
 index: 0,
 codec_name: 'h264',
 codec_long_name: 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10',
 profile: 'High',
 codec_type: 'video',
 codec_tag_string: 'avc1',
 codec_tag: '0x31637661',
 width: 1080,
 height: 1920,
 coded_width: 1080,
 coded_height: 1920,
 closed_captions: 0,
 has_b_frames: 2,
 sample_aspect_ratio: '1:1',
 display_aspect_ratio: '9:16',
 pix_fmt: 'yuv420p',
 level: 62,
 color_range: 'unknown',
 color_space: 'unknown',
 color_transfer: 'unknown',
 color_primaries: 'unknown',
 chroma_location: 'left',
 field_order: 'unknown',
 refs: 1,
 is_avc: 'true',
 nal_length_size: 4,
 id: 'N/A',
 r_frame_rate: '27000/1001',
 avg_frame_rate: '27000/1001',
 time_base: '1/27000',
 start_pts: 0,
 start_time: 0,
 duration_ts: 14014,
 duration: 0.519037,
 bit_rate: 52138429,
 max_bit_rate: 'N/A',
 bits_per_raw_sample: 8,
 nb_frames: 14,
 nb_read_frames: 'N/A',
 nb_read_packets: 'N/A',
 tags: [Object],
 disposition: [Object]
 }
 ],
 format: {
 filename: '/Users/name/images/output.mp4',
 nb_streams: 1,
 nb_programs: 0,
 format_name: 'mov,mp4,m4a,3gp,3g2,mj2',
 format_long_name: 'QuickTime / MOV',
 start_time: 0,
 duration: 0.52,
 size: 3383708,
 bit_rate: 52057046,
 probe_score: 100,
 tags: {
 major_brand: 'isom',
 minor_version: '512',
 compatible_brands: 'isomiso2avc1mp41',
 encoder: 'Lavf60.3.100'
 }
 },
 chapters: []
}



and here is from running
ffprobe
directly:

ffprobe '/Users/name/images/output.mp4'
ffprobe version 6.1.1 Copyright (c) 2007-2023 the FFmpeg developers
 built with Apple clang version 15.0.0 (clang-1500.1.0.2.5)
 configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/6.1.1_2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopenvino --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
 libavutil 58. 29.100 / 58. 29.100
 libavcodec 60. 31.102 / 60. 31.102
 libavformat 60. 16.100 / 60. 16.100
 libavdevice 60. 3.100 / 60. 3.100
 libavfilter 9. 12.100 / 9. 12.100
 libswscale 7. 5.100 / 7. 5.100
 libswresample 4. 12.100 / 4. 12.100
 libpostproc 57. 3.100 / 57. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/name/images/output.mp4':
 Metadata:
 major_brand : isom
 minor_version : 512
 compatible_brands: isomiso2avc1mp41
 encoder : Lavf60.3.100
 Duration: 00:00:00.52, start: 0.000000, bitrate: 52153 kb/s
 Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1080x1920 [SAR 1:1 DAR 9:16], 52138 kb/s, 26.97 fps, 26.97 tbr, 27k tbn (default)
 Metadata:
 handler_name : VideoHandler
 vendor_id : [0][0][0][0]
 encoder : Lavc60.3.100 libx264



This seems like it should be a fairly common scenario, but I have not been able to find examples of this, and the other questions about incorrect durations on Stack Overflow are about bigger differences (i.e. 3 seconds instead of 10 seconds: Wrong video duration when recording with ffmpeg).


Some other details:


- 

- I am running this through a Node.js script with
fluent-ffmpeg
, but I have also tried running the commands directly in the terminal and the result is the same. - I am fine with the output frames being .png / .jpg / other formats.
- I am fine with setting this to a different frame rate than the original as long as the two output videos end up with the same duration.
- One suspicious thing is that I set
-t 0.503333
when creating the video, but it doesn't seem to work as the result video showsduration: 0.519037
/00:00:00.52
.










Thank you for any help!


- I am running this through a Node.js script with
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