This video is created using ffmpeg command from a series of images with number and expected timestamp on it (assuming 120 fps constant frame rate):
ffmpeg -framerate 120 -i %03d.png -crf 0 -x264opts keyint=1:min-keyint=1 120.mp4
It's supposed to be constant frame rate, and all the frames are I frames. I expect frame 6 will show up exactly at time 0.05 second [0.05, 0.0583333), as the pts_time shown in ffmpeg and ffprobe:
[Parsed_showinfo_0 @ 0x7fba11404080] n: 6 pts: 768 pts_time:0.05 pos: 36021 fmt:yuv444p sar:0/1 s:1552x878 i:P iskey:1 type:I checksum:2CDED07A plane_checksum:[A86DBAAD C4CB8EF2 DDC586CC] mean:[163 133 121 ] stdev:[9.0 0.6 0.8 ]
[FRAME] media_type=video stream_index=0 key_frame=1 pkt_pts=768 pkt_pts_time=0.050000 pkt_dts=768 pkt_dts_time=0.050000 best_effort_timestamp=768 best_effort_timestamp_time=0.050000 pkt_duration=128 pkt_duration_time=0.008333 pkt_pos=36021 pkt_size=2531 width=1552 height=878 pix_fmt=yuv444p sample_aspect_ratio=N/A pict_type=I coded_picture_number=6 display_picture_number=0 interlaced_frame=0 top_field_first=0 repeat_pict=0 color_range=unknown color_space=unknown color_primaries=unknown color_transfer=unknown chroma_location=left [/FRAME]
But in reality, it shows up since 0.049943 second. I use ffmpeg to extract that time with 0.0001 second duration
ffmpeg -ss 00:00:00.049943 -i 120_keyint_1.mp4 -t 00:00:00.0001 out.mp4
and get this video, which shows frame 6.
I also tried playing this video on chrome, and set the currentTime of videoNode. It shows frame 5 at 0.049943, but shows frame 6 since 0.049968 (before 0.05!).
However, I tried another encoding method and get another constant frame rate video:
ffmpeg -framerate 120 -i %03d.png -vcodec libx264 -f mp4 -movflags faststart 120.mp4
theoretically frame 6 should also appear in time range [0.05, 0.0583333), but in Chrome frame 6 will not show up until currentTime >= 0.051 second. More interestingly, I get frame 6 at 0.049943 second using ffmpeg, the same extraction command above.
Does this mean in MPEG4 h.264 video, we cannot rely on pts_time from ffmpeg to determine exact show time of a specific frame and it's video player specific?
