How do I render a video from a list of time-stamped images?

Question

I have a directory full of images following the pattern <timestamp>.png, where <timestamp> represents milliseconds elapsed since the first image. input.txt contains a list of the interesting images:

file '0.png'
file '97.png'
file '178.png'
file '242.png'
file '296.png'
file '363.png'
...

I am using ffmpeg to concatenate these images into a video:

ffmpeg -r 15 -f concat -i input.txt output.webm

How do I tell ffmpeg to place each frame at its actual position in time instead of using a constant framerate?

Answer 1

Following LordNeckbeard's suggestion to supply the duration directive to ffmpeg's concat demuxer using the time duration syntax, input.txt looks like this:

file '0.png'
duration 0.097
file '97.png'
duration 0.081
file '178.png'
duration 0.064
file '242.png'
duration 0.054
file '296.png'
duration 0.067
file '363.png'

Now ffmpeg handles the variable framerate.

ffmpeg -f concat -i input.txt output.webm

Here is the C# snippet that constructs input.txt:

Frame previousFrame = null;

foreach (Frame frame in frames)
{
    if (previousFrame != null)
    {
        TimeSpan diff = frame.ElapsedPosition - previousFrame.ElapsedPosition;
        writer.WriteLine("duration {0}", diff.TotalSeconds);
    }

    writer.WriteLine("file '{0}'", frame.FullName);
    previousFrame = frame;
}

Answer 2

Appears your images are non standard frame rate...One option would be to duplicate the appropriate image "once per millisecond" [i.e. for

 file '0.png'
 file '97.png'

duplicate file 0.png 96 times, so it becomes 0.png 1.png 2.png etc. (or use symlinks, if on linux).

Then you can combine them using the normal image inputter [with input rate of 1ms/frame]. https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20from%20images