[Ffmpeg-devel] [PATCH] remove drop timecode flag

[Baptiste Coudurier]

Michael Niedermayer wrote:
> Hi
> 
> On Sun, Apr 15, 2007 at 08:27:55AM -0700, Trent Piepho wrote:
>> On Sun, 15 Apr 2007, Michael Niedermayer wrote:
>>> attached patch removes the drop timecode encoding support
>>> reasoning is that iam not aware of any use (not even obscure) of this feature
>> Isn't the timecode wrong if you don't use drop frame timecode for NTSC?
>>
>> e.g., the timecode after exactly 1 hour of NTSC video will be
>> '00:59:56:12', which is short 3 seconds and 18 frames from one hour.  With
>> drop frame timecode, the timecode after an hour would be '01:00:00:00',
>> since 108 timecodes would have been skipped over.
> 
> timecodes are codec specific

Read the paper:

Time Code is a method of accurately identifying each frame in a video
sequence. It is an international standard jointly developed by the
Society of Motion Picture and Television Engineers   (SMPTE) and the
European Broadcasting Union  (EBU). VTR transports and associated
equipment use SMPTE/EBU timecode values for Frame Accurate cueing.

SMPTE/EBU Time Code values are represented in four (8-bit) bytes, where
each byte contains two BCD encoded digits, the tens digit and the unit
digit. The bytes represent values for Hours, Minutes, Seconds and Frames
accordingly.

> if a codec uses the rounded up fps as timebase then the timecode must be
> scaled accordingly and if needed the drop flag be set, its not the user
> applications job to do this

User can decide to use non-drop frame timecode even for NTSC. In
production it tends be more common since workflows are IT based, now
Broadcasters still use drop frame timecode because of tapes and the need
of real time correspondance.

> also the drop frame flag=1 is only allowed for 30000/1001 fps (per mpeg2 spec)
> for 24000/1001 for example you need a different solution anyway so the
> question is why not use that solution too for 30000/1001?

24000/1001 is not used (yet ?) in broadcast environment.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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