[FFmpeg-user] prores4444 to dpx: colourshift & translation, dpxenc.c patch

[ArnoB]

Hello,

First, my apologies for cross posting, but I think this belongs
in the dev-list.

I dug into the code and managed to find a very simple solution
for the problem I encountered. I added a line to libavcodec/dpexenc.c
diff dpxenc.new.c dpxenc.c:

215d214
<     write32(buf + 808, HEADER_SIZE); /* data offset */

(I hope I'm providing this the correct way.)


Another thing I found is that the dpx-encoding header is
very minimal and the header offset should be bigger according
to the SMPTE specs.

this leads me to the question if it's ok for me to supply a patch
that upgrades the DPX encoding header to version 2.0?
Here are the official papers (although I was told SMPTE never
actually made DPX an official standard because of the lack of
tape-names in the header, basically making it impossible to
use in a tv/film environment if you just use the standard):
http://www.simplesystems.org/users/bfriesen/dpx/S268M_Revised.pdf

thanks in advance,

Arno Beekman




On 21 feb 2013, at 21:43, Paul B Mahol wrote:

> On 2/21/13, Mark Himsley <mark.himsley at gmail.com> wrote:
>> On 20 Feb 2013 20:00, "ArnoB" <ffmpeg at rgbaz.eu> wrote:
>>> 
>>> Hello!
>>> 
>>> I'm trying to convert a prores4444 quicktime with gamma 2.2 to
>>> a dpx sequence with the following command:
>>> 
>>> % ffmpeg -i prores4444g2.2_v01.mov prores.%02d.dpx
>>> 
>>> In the resulting DPX sequence I have the following errors:
>>> -the DPXs are tagged as being sRGB. manually switching my program's
>>> reader to 2.2 makes them look ok;
>>> 
>>> -there is a colourshift of around 120DEG. My prores file contains a
>> colourwheel
>>> so it's easy to spot. green becomes blue, red becomes green and blue
>>> becomes red;
>> -also there's a translation in the X  of +277 pixels. the missing part
>>> is wrapped around and visible on the other side:
>> 
>> What you're saying is that FFmpeg says it's outputting rgb but other
>> software is interpreting it as bgr.
>> 
>> Have you tried asking FFmpeg for a bgr format?
>> 
> 
> That is first info. Looking at code both encoder and decoder support
> only rgb (no bgr at all).
> 
>> 
>> --
>> 
>> Mark
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