[FFmpeg-user] Extracting frames from 59.94 FPS video - only every other frame is different

[Gyan Doshi]

On 12/1/2017 10:42 PM, Will Price wrote:
> Hello,
> 
> I'm having a strange problem when extracting frames from a video recorded from a GoPro HERO 5 Black camera (1080p, 60FPS, Linear FOV). When I view the extracted frames it appears that every two frames is a duplicate of one another, i.e. frames 1 and 2 look the same, frame 3 shows a change, but frame 4 again looks the same as 3.

Mostly a duplicate.

ffprobe GOPR0325.MP4 -show_entries packet=pts_time,size -select_streams 
v -read_intervals %+#20 -of compact

shows

packet|pts_time=0.000000|size=365376
packet|pts_time=0.016683|size=5512
packet|pts_time=0.033367|size=72063
packet|pts_time=0.050050|size=15364
packet|pts_time=0.066733|size=63619
packet|pts_time=0.083417|size=17909
packet|pts_time=0.100100|size=75613
packet|pts_time=0.116783|size=17061
packet|pts_time=0.133467|size=72911
packet|pts_time=0.150150|size=21295
packet|pts_time=0.166833|size=77609
packet|pts_time=0.183517|size=20959
packet|pts_time=0.200200|size=86407
packet|pts_time=0.216883|size=16628
packet|pts_time=0.233567|size=87910
packet|pts_time=0.250250|size=22231
packet|pts_time=0.266933|size=92910
packet|pts_time=0.283617|size=11857
packet|pts_time=0.300300|size=90740
packet|pts_time=0.316983|size=24167

Every other frame's size looks to be much smaller. The first frame is an 
I-frame and all others are P-frames. When x264 repeats a frame, the size 
is usually up to a few hundred bytes.

Is the camera truly registering 60 times a second?

Gyan