[FFmpeg-user] Find Change from Black and White to Color Frames

[Dave Rice]

Hi Bill,

> On Feb 7, 2015, at 9:44 PM, Bill Brazeal <bill at billbrazeal.com> wrote:
> 
> I would like to be able to automatically search through a video file and find the point at which the video changes from black and white to color.  This is a video file obtained by a security camera that the video is black and white when its dark outside and then it changes to color when there is enough light.  I would like to automatically trim out the black and white frames leaving only the color.  So I need to be able to find the point at which the video changes from black and white to color (morning), then again from color to black and white (evening).  Is there any way to do this with ffmpeg?
> 
> It has been suggested that I might be able to use the signalstats filter to do this.  I am very much a novice at using ffmpeg so if someone could provide a good example of how to do this, that would be very much appreciated.

Yes the signalstats filter reports on the average saturation level of each frame, so if you try:

ffprobe -f lavfi -i movie=SECURITYCAM.avi,signalstats -show_entries frame_tags=lavfi.signalstats.SATAVG -of flat

Your black and white footage should report like:
frames.frame.261.tags.lavfi_signalstats_SATAVG="0"

while color frames will have a value above zero. You'll then need to do some scripting to identify the transition points to use as in and out points in your edits.

I don't think it's feasible at this point but I wonder how feasible it would be to pull the metadata values into expressions in the select filter.
A dream:
ffmpeg -i mixed.avi -vf signalstats,select='gt(lavfi.signalstats.SATAVG\,0)' -c:v libx264 color_frames_only.mp4

Best Regards,
Dave Rice

> Thanks,
> 
> Bill