ffprobe - shuffled frame metadata

Question

I'm using mkvmerge to combine a mp4 CFR video with a text file containing VFR timestamps. The command used was

mkvmerge --timestamps 0:timestamps.txt input_video.mp4 -o output_video.mkv

Where the textfile timestamps.txt was of a v2 timestamp format. Here are the first few entries

# timecode format v2
0
6
21
36
53
71
87
103
123

I'm trying to print these timestamps back out with

ffprobe -v 0 -show_entries packet=pts,duration -of compact=p=0:nk=1 -select_streams v output_video.mkv

But I receive shuffled entries

0|6
6|15
21|15
36|17
53|18
123|15
87|16
71|16
103|20

If I read the frames with PyAV for example, I get the values in correct order.

import av
c = av.open("output_video.mkv")
for frame in c.decode(video=0):
     print(frame.pts)

Output:

0
6
21
36
53
71
87
103
123

Am I using ffprobe incorrectly? Any help would be very welcome!

Answer 1

If the video stream has B-frames then future P-frames which act as reference for B-frames are encoded first and stored in that order. They are reordered after decoding.

For ffprobe, the entries in packet are arranged in decode or storage order. In frames , they are decoded and arranged in presentation order.