[FFmpeg-devel] [PATCH] lavc/dnxhddata: fix bitrates for cid 1251 and 1252 in cid table

Matthieu Bouron matthieu.bouron at gmail.com
Tue Jan 22 16:31:14 CET 2013

On Tue, Jan 22, 2013 at 4:04 PM, Tim Nicholson <nichot20 at yahoo.com> wrote:
> On 22/01/13 13:34, Matthieu Bouron wrote:
>> On Tue, Jan 22, 2013 at 2:18 PM, Tim Nicholson <nichot20 at yahoo.com> wrote:
>>> On 21/01/13 20:14, Matthieu Bouron wrote:
>>>> ---
>>>> Hi there,
>>>> According to SMPTE S2019-1, bitrates should be:
>>>>   - 180Mbps for cid 1251 at 50fps,
>>>>   - 120Mbps for cid 1252 at 50fps.
>>> Looking at Annex F in my SMPTE S2019-1-2008 suggests 25fps figures are
>>> wrong too..
>>> cid 1251 is { 90, 80, 180, 220 }
>>> cid 1252 is { 60, 60, 120, 145 }
>> The 75Mbps value "may" refer to the 29.97fps profile (which is
>> declared here: http://www.avid.com/static/resources/FR/documents/dnxhd.pdf
>> but not in the S2019). The single 60Mbps value refers here to the
>> 23.976fps and 25fps profiles (this is how i understand it).
> So the original values are based on Avid's spec (although the 75 should
> be 72), and you want to change some of them to conform to SMPTE VC3 spec?
> It is unhelpful that the values sources are not documented, since you
> were quoting SMPTE I assumed the values that I suggested also needed a
> tweak were for 25fps since 29.97fps does not exist in the cid's under
> discussion...
> What is your thinking behind having values that appear to be drawn from
> two different specification sources? Is this wise?

I do not know where the actual values came from, maybe Baptiste can
comment on this.
The only document i actually trust is the SMPTE S2019-1 and the avid
document i linked was found by random googling when i was trying to
look for a 75Mbps 720p profile.

I tried to correct thoses values to be more consitent with the SMPTE
spec since the smpte bitrate (180) is used for the cid 1250 50fps but
not for the cid 1251 50fps (175 instead of 180).

IMHO, mixing the missing dnx profiles with the vc3 ones sounds ok
untill those dnx profiles are effectively supported by ffmpeg.



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