ffmpeg video length is 0 when concatenating pictures

Question

I'm trying to concatenate individual frames, but the video length is 0 and all frames seemingly play at once. Iv'e tried increasing the video length in ffmpeg and changing the frame rate.

os.system('ffmpeg -f concat -i List_tb.txt -c copy output.mp4')
os.system("ffmpeg -i output.mp4 -filter:v fps=fps=120 output_temp.mp4")
os.system("ffmpeg -i output_temp.mp4 -filter:v setpts=8.0*PTS final.mp4")

also the frame rate is the amount of frames

Rerun the command with -report added and look in the working directory. — Gyan, Nov 09 '19 at 15:56
ffmpeg started on 2019-11-09 at 19:16:57 Report written to "ffmpeg-20191109-191657.log" Command line: "C:\\FFmpeg\\bin\\ffmpeg.exe" -f concat -safe 0 -i List_tb.txt -c copy output.mp4 -report ffmpeg version N-94335-g9869e21776 Copyright (c) 2000-2019 the FFmpeg developers built with gcc 9.1.1 (GCC) 20190716 — iftach freund, Nov 09 '19 at 16:26
You don't **concat** (stitch) PNG bytes together and call it an MP4 file. I don't know how that even worked with `-codec copy`. — VC.One, Nov 10 '19 at 04:23
PS try: `ffmpeg -loop 1 -i List_tb.txt -t 5 -c:v libx264 -crf 20 -pix_fmt yuv420p output.mp4`. Alternatively try [this advice](https://stackoverflow.com/a/24966617/2057709). — VC.One, Nov 10 '19 at 04:33

score 0 · Accepted Answer · answered Nov 10 '19 at 06:23

Since images don't have inherent timestamps, the concat demuxer is failing to generate a smooth monotonic sequence of timestamps for the packets it generates. You can work around this by specifying a duration directive for each file, within the list i.e.

file '-1.1257558476894771_10_1_0j.png'
duration 0.04
file '-0.8103308013367797_10_1_0j.png'
duration 0.04
file '1.0805993584315776_10_1_0j.png'
duration 0.04
...

where 0.04 is the duration in seconds for one frame at 25 fps.

ffmpeg video length is 0 when concatenating pictures

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