[FFmpeg-trac] #9390(undetermined:new): Wrong FPS used for timecode computation mangles timecodes

[FFmpeg]

#9390: Wrong FPS used for timecode computation mangles timecodes
-------------------------------------+-------------------------------------
             Reporter:  Marcelo      |                    Owner:  (none)
  Magnasco                           |
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:  timecode     |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Old description:

> Summary of the bug:
> ffprobe reports the wrong timecode for footage generated by my GoPro 9
> Black cameras. The error is due to ffprobe/ffmpeg mangling the frame rate
> from 29.97 or 59.94 to 29/1 or 59/1.
>
> For example, footage with start timecode 10:59:47:14, 29.97fps, is
> reported by ffprobe as having start timecode 11:22:32:16, which is equal
> to (10:59:47:14)*30/29.
>
> How to reproduce:
> {{{
> % ffprobe GP001.MP4
> where GP001.MP4 is a 29.97fps clip from a GoPro, includes in its output a
> black-backgrounded line
> [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7ffb6b80ac00] Using non-standard frame rate
> 29/1
>
> The incorrect framerate 29 is used to convert the timecode from frames-
> since-midnight to HH:MM:SS:FF format.
>
> ffmpeg version 4.2.1-tessus
> built with Apple LLVM version 10.0.1 (clang-1001.0.46.4)
>
> }}}
> Patches should be submitted to the ffmpeg-devel mailing list and not this
> bug tracker.

New description:

 Summary of the bug:
 ffprobe reports the wrong timecode for footage generated by my GoPro 9
 Black cameras. The error is due to ffprobe/ffmpeg mangling the frame rate
 from 29.97 or 59.94 to 29/1 or 59/1.

 For example, footage with start timecode 10:59:47:14, 29.97fps, is
 reported by ffprobe as having start timecode 11:22:32:16, which is equal
 to (10:59:47:14)*30/29.

 How to reproduce:
 {{{
 % ffprobe GP001.MP4
 where GP001.MP4 is a 29.97fps clip from a GoPro, includes in its output a
 black-backgrounded line
 [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7ffb6b80ac00] Using non-standard frame rate
 29/1

 The incorrect framerate 29 is used to convert the timecode from frames-
 since-midnight to HH:MM:SS:FF format.

 PLEASE SEE THE ATTACHED FILE AND NOTE

 ffmpeg version 4.2.1-tessus
 built with Apple LLVM version 10.0.1 (clang-1001.0.46.4)

 }}}
 Patches should be submitted to the ffmpeg-devel mailing list and not this
 bug tracker.

--
Comment (by Marcelo Magnasco):

 NOTE: the 2MB file size limit prevented me from attaching most of the
 files in the set. I was only able to attach file C5GL010008.mp4 . I can
 submit all five files in the testing set through a different channel of
 your choice (i.e. dropbox link).

 I made three clips (plus two LRV previews) with a GoPro Hero9 Black
 camera, pointing at a timeslate running on my desktop. The camera's clock
 is synced to my phone not to the slate so it's about one sec off from the
 25fps timecode (which should be correct time of day).

 GoPro cameras list all their FPSs as 60/120/240 but they are in fact NTSC
 59.94... etc.

 C5GX010007.MP4 1080p/240fps
 C5GH010008.MP4 1080p/120fps
 C5GL010008.mp4 480p/60fps preview of 008
 C5GH010009.MP4 1080p/60fps
 C5GL010009.mp4 480p/60fps preview of 009

 Timecode of first frame in movie and timecode displayed on slate on first
 frame nondrop/30, vs. timecode reported by ffprobe

 @@@@@@@@@       |.  1st frame.          |   on slate.           |.
 ffprobe
 C5GX010007.MP4  | 08:54:16:144  | 08:54:17:13   | 08:56:30:113
 C5GH010008.MP4  | 08:55:05:017  | 08:55:05:27   | 08:59:34:81
 C5GL010008.mp4  | 08:55:04:53   | 08:55:05:27   | 09:04:09:02
 C5GH010009.MP4  | 08:55:50:00   | 08:55:51:04   | 09:04:54:54
 C5GL010009.mp4  |08:55:50:00    | 08:55:51:04   | 09:04:54:54

 Please note these are not small errors, ffprobe is off by many minutes,
 the more the slower the sampling rate.

 You can compute easily that in the case of the file attached, the timecode
 reported by ffprobe, 09:04:09:02, equals (60/59)*08:55:04:53
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9390#comment:2>
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