Re: [libdv-dev] [PATCH] dv_encode_timecode_fps

[Roman S. <rv...@su...>]

On Wed, Dec 08, 2004 at 01:30:43PM -0500, Richard Baverstock wrote:
> It's come to my attention that this doesn't perfectly handle drop-frame
> timecode correctly still, but opens the door for it.
> 
> Quote from an email from Phil Rhodes:
> 
> "Just to make this ultra clear, all minutes except tens in DF timecode
> look like this:
> 
> 00:00:59:28 - 00:00:59:29 - 00:01:00:02 - 00:01:00:03

  The way I implemented it in ffmpeg's DV codec is:

          /*
           * LTC drop-frame frame counter drops two frames (0 and 1) every
           * minute, unless it is exactly divisible by 10
           */
          ltc_frame = (c->frames + 2*ct/60 - 2*ct/600) % c->sys->ltc_divisor;

Thanks,
Roman.
 
> Also refer to Adobe's writeup at
> http://www.ledet.com/coolstuff/software/premiere/timecode.pdf - I
> haven't looked it over, but I presume they know what they're doing."
> 
> 
> Patch in a little bit, exams this and next week.
> 
> On Wed, 2004-12-08 at 10:52 -0500, Richard Baverstock wrote:
> > Attached is a patch that adds the function "dv_encode_timecode_fps()" to
> > headers.c and the public api of libdv. The function acts exactly like
> > dv_encode_timecode(), but takes an additional parameter (the frame
> > rate). This allows drop frame/non-drop frame timecodes to be encoded, as
> > well as non-pal or ntsc frame rates such as film.
> > 
> > dv_encode_timecode() is maintained so as not to break the api, and
> > serves as a wrapper to dv_encode_timecode_fps() (with the same behavior
> > as before - 30 fps assumed for NTSC).
> > 
> > write_timecode_13() is modified to take a double parameter instead of an
> > integer to determine the frame rate. In write_subcode_blocks(), 30 fps
> > is again assumed to be the frame rate for ntsc when write_timecode_13()
> > is called.
> > 
> > While this fixes the dv_encode_timecode() issue for non-drop frame
> > timecode, you can see there are some wrong assumptions still in the rest
> > of libdv. I didn't want to delve any further into the library until I
> > got some feedback. In some cases, it will be necessary to change the
> > internal api (write_subcode_blocks() for example will have to take an
> > fps parameter), and the public api (an fps field in dv_encoder_t).
> > 
> > Anyways, with this patch, everything works as before unless you use
> > dv_encode_timecode_fps().
> > 
> > 
> > 
> > 
> > Richard
> 
> 
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