Find a frame in a video from an image using FFmpeg

Question

I have a small 30 second video that was taken from a long 10h video and processed. I am trying to find the position of the first frame from the 30 second video in the long 10h video. Because the small video has been processed, checksuming the frames doesn't work so I tried saving the first frame as an image,

ffmpeg -i clip.mp4 -qmin 1 -qscale:v 1 -vframes 1 -f image2 firstframe.jpg

and then using that image using that image to search it like this:

ffmpeg -i original_stream.ts -loop 1 -i firstframe.jpg -an -filter_complex "blend=difference:shortest=1,blackframe=99:32" -f null -

This sometimes works, but at times it returns more than 1 frame no matter what blackframe I'm using.

Also, if I try to use -ss to skip a part of the stream it doesn't return the precise time. For example,

1. Without -ss:

   [Parsed_blackframe_1] frame:44250 pblack:99 pts:66375000 t:737.500000 type:P last_keyframe:44160
   

2. With -ss 735:

   [Parsed_blackframe_1] frame:90 pblack:99 pts:227820 t:2.531333 type:P last_keyframe:0
   

3. The times from the two examples above don't match up. Since t in example #1 is 737.500000, I would expect t in example #2 to be 2.500000, not 2.531333 :

   737.500000-735=2.500000
   

4. Also, 735 x 90000 + 227820 ≠ 66375000

I think I can use the frame number as that seems to be the most accurate.

The whole reason I'm doing this is to extract the exact audio from the original stream that matches the 30 second clip so I need the exact position.

Answer 1

input_video.mp4 is the name of the video file from which you want to extract a frame. output_frame.png is the name you want to give to the extracted frame. 3 is the frame number to extract. You can change this number to the frame you want. Make sure to count from 0, so the first frame is 0, the second frame is 1, and so on.

Thanks, Dealsdepot