On Tue, Jun 30, 2020 at 12:28:34PM +0200, Nicolas George wrote:
> lance.lmw...@gmail.com (12020-06-30):
> > From: Limin Wang <lance.lmw...@gmail.com>
> >
> > AV_FRAME_DATA_S12M_TIMECODE is public API, so user need to know its format
> > by the API header instead of reading the code.
> >
> > Signed-off-by: Limin Wang <lance.lmw...@gmail.com>
> > ---
> > libavutil/frame.h | 4 ++--
> > libavutil/timecode.h | 16 +++++++++++++++-
> > 2 files changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/libavutil/frame.h b/libavutil/frame.h
> > index 3fb8c56..c694b12 100644
> > --- a/libavutil/frame.h
> > +++ b/libavutil/frame.h
> > @@ -162,8 +162,8 @@ enum AVFrameSideDataType {
> > /**
> > * Timecode which conforms to SMPTE ST 12-1. The data is an array of 4
> > uint32_t
> > * where the first uint32_t describes how many (1-3) of the other
> > timecodes are used.
> > - * The timecode format is described in the
> > av_timecode_get_smpte_from_framenum()
> > - * function in libavutil/timecode.c.
> > + * The timecode format is described in the comments of
> > av_timecode_get_smpte_from_framenum()
> > + * function in libavutil/timecode.h.
> > */
> > AV_FRAME_DATA_S12M_TIMECODE,
> >
> > diff --git a/libavutil/timecode.h b/libavutil/timecode.h
> > index ab38e66..b1c1887 100644
> > --- a/libavutil/timecode.h
> > +++ b/libavutil/timecode.h
> > @@ -61,7 +61,21 @@ int av_timecode_adjust_ntsc_framenum2(int framenum, int
> > fps);
> > * @param tc timecode data correctly initialized
> > * @param framenum frame number
> > * @return the SMPTE binary representation
> > - *
>
> > + * the format description as follows, note it's in system byte order:
>
> Better avoid contractions in documentation.
>
> The result is uint32_t, not char[4]: there is no byte order.
Sure, will remove the note.
>
> > + * 31b: color frame flag (0: unsync mode, 1: sync mode)
> > + * 30b: drop frame flag (0: non drop, 1: drop)
> > + * 28b,29b: tens of frames
> > + * 24-27b: units of frames
> > + * 23b: PC (NTSC) or BGF0 (PAL)
> > + * 20b,22b: tens of seconds
> > + * 16-19b: units of seconds
> > + * 15b: BGF0 (NTSC) or BGF2 (PAL)
> > + * 12b,13b: tens of minutes
> > + * 8-11b: units of minutes
> > + * 7b: BGF2 (NTSC) or PC (PAL)
> > + * 6b: BGF1
> > + * 4b,5b: tens of hours
> > + * 0b-3b: units of hours
>
> It seems more logical in the opposite order.
>
> I do not think this b suffix is very standard. Better be explicit:
>
> * bits 24-27: units of frames
>
> Also, no reason to make a special case when there are exactly two.
>
> And since several numbers are stored the same way, I would suggest to
> regroup:
>
> * bits 8-13: minutes, in BCD
> * ...
> * BCD numbers (6 bits): 4 lower bits for units, 2 higher bits for tens.
Below is my update by your suggestion, please help to review.
MPTE binary representation
+ * the format description as follows:
+ * bits 0-5: hours, in BCD
+ * bits 6: BGF1
+ * bits 7: BGF2 (NTSC) or PC (PAL)
+ * bits 8-13: minutes, in BCD
+ * bits 15: BGF0 (NTSC) or BGF2 (PAL)
+ * bits 16-21: seconds, in BCD
+ * bits 23: PC (NTSC) or BGF0 (PAL)
+ * bits 24-29: frames, in BCD
+ * bits 30: drop frame flag (0: non drop, 1: drop)
+ * bits 31: color frame flag (0: unsync mode, 1: sync mode)
+ * @note BCD numbers (6 bits): 4 lower bits for units, 2 higher bits for tens.
> > * you do NOT have to call av_timecode_adjust_ntsc_framenum2().
> > * @note The frame number is relative to tc->start.
>
> Regards,
>
> --
> Nicolas George
--
Thanks,
Limin Wang
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