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

Baptiste Coudurier baptiste.coudurier
Mon Apr 16 14:34:19 CEST 2007

Michael Niedermayer wrote:
> Hi
> On Mon, Apr 16, 2007 at 01:08:44PM +0200, Baptiste Coudurier wrote:
>> Michael Niedermayer wrote:
>>> Hi
>>> On Mon, Apr 16, 2007 at 11:49:14AM +0200, Baptiste Coudurier wrote:
>>> [...]
>>>>>> This way the SMPTE frame ID will _roughly_ correspond to the
>>>>>> "hours:minutes:seconds:(1/30th seconds)" of the frame's time.  It is not
>>>>>> exact in NTSC, sometimes being off by up to .06 seconds.  But it does not
>>>>>> have an error that accumulates over time, as so is good enough for editing
>>>>>> and cueing, which is what it is used for.
>>>>> wrong it does have an error which accumulates over time and this is another
>>>>> reason why its a very bad idea
>>>>> the drop frame timecode calculation end up at 2997/100 instead of 30000/1001
>>>>> also what exactly is the problem with just setting the true sec/min/hour
>>>>> and frame within that second as mandated by mpeg4 in the mpeg2 case too
>>>>> if its really just an abstract ID?
>>>> I found this thread in mp4-tech related to mpeg4 timing:
>>>> http://lists.mpegif.org/pipermail/mp4-tech/2001-October/000268.html
>>>> Does lavc encoder use vop_time_increment_resolution, modulo_time_base
>>>> and vop_time_increment parameters, as mentioned ?
>>> your question makes no sense, the author of the mail to which you refer
>>> is confused, there is no drop frame, no compensation,
>>> no random update and no inexactness in mpeg4s timecode and timestamps
>> I was refering to gary's explanation obviously.
>> "The time of each individual VOP is governed by the
>> use of that time_code in conjunction with the
>> vop_time_increment_resolution, modulo_time_base, and vop_time_increment
>> parameters (along with the previously-mentioned fixed_vop_rate flag and
>> fixed_vop_time_increment parameter)."
>> I repeat my question:
>> Does lavc uses all those parameters mentioned for mpeg4 as mentioned ?
> yes
>> Is is possible to retrieve time of each individual VOP in NTSC ? That's
>> an interesting feature.
> yes
>> Unfortunately, mpeg2 was not designed like mpeg4.
> yes and its IMO not the user (application) job to know that and set drop
> timecode and scale the timecode differently for mpeg4 and mpeg2

Well, how can lavc use non drop frame format for NTSC in mpeg2,

Considering time code is unique frame address defined by SMPTE 12M, and
that address will be used by my AVID editing sytem and all my worklow,
which is configured to work as non drop frame, without any real time
correspondance, only coded frame numbering.

"The frames shall be numbered successively according to the counting
mode (drop frame or nondrop frame) as described below:

4.2.1 Nondrop frame ---- Uncompensated mode

Frames shall be numbered 0 through 29, succes-
sively, with no omissions."

Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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