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I am trying to generate synthetic video using FFmpeg.

I want the frame rate to be 10 fps, and I want testsrc counter to advance every frame.

Problem:
When the output file is mp4, the first video frame is duplicated 10 times.

Question:
Is it a bug in FFmpeg, or a problem in the command line arguments?

I am using the following command: 

ffmpeg -y -r 10 -f lavfi -i testsrc=duration=10:size=192x108:rate=1 -c:v libx264 vid.mp4
  • The reason for setting rate=1 is for the counter to advance on each frame.
    The generated source pattern is designed to advance the counter every second.
  • The reason for setting -r 10 before the input, is for "remuxing" the video at 10 fps, and ignoring the timestamps of the input.

I found the syntax in the following post: Using ffmpeg to change framerate:

Remux with new framerate

ffmpeg -y -r 24 -i seeing_noaudio.h264 -c copy seeing.mp4

When the output file is AVI it's working correctly (first frame is not duplicated): 

ffmpeg -y -r 10 -f lavfi -i testsrc=duration=10:size=192x108:rate=1 -c:v libx264 vid.avi

When generating AVI at 1 fps, and Remux to mp4 at 10 fps, there is a different problem:
The first and second frames are duplicated twice, and the last frame is missing.
Here are the commands: 

ffmpeg -y -f lavfi -i testsrc=duration=10:size=92x54:rate=1 -c:v libx264 -r 1 vid.avi
ffmpeg -y -r 10 -i vid.avi -c:v copy -r 10 vid.mp4

Parsing the mp4 video to PNG images: 

ffmpeg -i vid.mp4 %02d.png

Result:
enter image description here
The first frame is duplicated 10 times.

Parsing the AVI video to PNG images:
Result:
enter image description here
There are 10 frames as expected.

Rotem
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1 Answers1

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This is likely something to do with the initial timebase but I can't test for a few days. For now, use

ffmpeg -y                                    \
       -f lavfi                               \
       -i                                      \
        testsrc=duration=10:size=192x108:rate=1 \
       -vf                                       \
        setpts=N/10/TB                            \
       -r 10                                       \
       -c:v                                         \
        libx264                                      \
        vid.mp4
user3666197
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Gyan
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  • Thank you. It's working when moving the `-r 10` to the input: `ffmpeg -r 10 -y -f lavfi -i testsrc=duration=10:size=192x108:rate=1 -vf setpts=N/10/TB -c:v libx264 vid.mp4`. I still don't understand if it's a bug in FFmpeg... – Rotem Feb 06 '20 at 15:20