Mov file has more frames than written/Possible iOS AVAsset writer usage issue

Question

I am manually generated a .mov video file.

Here is a link to an example file: link, I wrote a few image frames, and then after a long break wrote approximately 15 image frames just to emphasise my point for debuting purposes. When I extract images from the video ffmpeg returns around 400 frames instead of the 15-20 I expected. Is this because the API i am using is inserting these image files automatically? Is it a part of the .mov file format that requires this? Or is it due to the way the library is extracting the image frames from the video? I have tried searching the internet but could not arrive at an answer.

My use case is that I am trying to write the current "sensor data" (from core motion) from core motion while writing a video. For each frame I receive from the camera, I use "AppendPixelBuffer" to write the frame to the video and then

Thanks for any help. The end result is I want a 1:1 ratio of Frames in the video to rows in the CSV file. I have confirmed I am writing the CSV file correctly using various counters etc. So my issue is cleariy the understanding of the movie format or API.

Thanks for any help.

Answer 1

UPDATED It looks like your ffmpeg extractor is wrong. To extract only the timestamped frames (and not frames sampled at 24Hz) in your file, try this:

ffmpeg -i video.mov  -r 1/1 image-%03d.jpeg

This gives me the 20 frames expected.

OLD ANSWER

ffprobe reports that your video has a frame rate of 2.19 frames/s and a duration of 17s, which gives 2.19 * 17 = 37 frames, which is closer to your expected 15-20 than ffmpeg's 400.

So maybe the ffmpeg extractor is at fault?

Hard to say if you don't show how you encode and decode the file.