From: "Robert Kjettrup" <AE-List@media-motion.tv>
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In-Reply-To: <list-5564697@media-motion.tv>
References: <list-5564697@media-motion.tv>
Date: Thu, 4 Sep 2014 19:35:51 +0200
Message-ID: <CAFu=taZzUEkZ7zhwFdiXbvyM83EzPP_Oq_RAvC=w9+scCZe41w@mail.gmail.com>
Subject: Re: [AE] Compression issues article
To: After Effects Mail List <AE-List@media-motion.tv>
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> Interesting.  One issue I would anticipate is that H.264 is typically
> 4:2:0, so if you save in another YUV format, FFmpeg would have
> to convert it, possibly by converting back to RGB.  I would hope
> there was some 4:2:0 YUV format that wouldn't involve those issues,
> but I don't know.
>
> Brendan

Doesnt an encoder need to full decode the file and get an RGB image before
re-encoding it again? That is what i was thinking and caused the colorshift
i was seeing, that FFmpeg did a "wrong" YUV -> RGB conversion. Maybe it is
possible to keep it in keep it in YUV space without the color conversion,
it should be when i think about it.

It has been a while since i tested this, and some things might have been
improved with newer versions of FFmpeg. But i did test Uncompressed YUV,
ProRes HQ and DNxHD 185, and they are all in YUV 4:2:2 and all showed
colorshifts. FFmpeg wouldnt read DNxHD 444 or ProRes 444 so i couln't check
those, but it might be able to now, dont know.
I think DNxHD444 is RGB, but ProRes444 is still YUV??? So it could be
interesting to test those again if they are read now.

Robert

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote"><div=
>&gt; Interesting.=C2=A0 One issue I would anticipate is that H.264 is typi=
cally=C2=A0<br></div><div>&gt; 4:2:0, so if you save in another YUV format,=
 FFmpeg would have=C2=A0</div>

<div>&gt; to convert it, possibly by converting back to RGB.=C2=A0 I would =
hope=C2=A0</div><div>&gt; there was some 4:2:0 YUV format that wouldn&#39;t=
 involve those issues,=C2=A0</div><div>&gt; but I don&#39;t know.<br></div>=
<div>&gt;</div>

<div>&gt;=C2=A0<span style=3D"color:rgb(80,0,80)">Brendan</span></div><div>=
<span style=3D"color:rgb(80,0,80)"><br></span></div><div>Doesnt an encoder =
need to full decode the file and get an RGB image before re-encoding it aga=
in? That is what i was thinking and caused the colorshift i was seeing, tha=
t FFmpeg did a &quot;wrong&quot; YUV -&gt; RGB conversion. Maybe it is poss=
ible to keep it in keep it in YUV space without the color conversion, it sh=
ould be when i think about it.</div>

<div><br></div><div>It has been a while since i tested this, and some thing=
s might have been improved with newer versions of FFmpeg. But i did test Un=
compressed YUV, ProRes HQ and DNxHD 185, and they are all in YUV 4:2:2 and =
all showed colorshifts. FFmpeg wouldnt read DNxHD 444 or ProRes 444 so i co=
uln&#39;t check those, but it might be able to now, dont know.</div>

<div>I think DNxHD444 is RGB, but ProRes444 is still YUV??? So it could be =
interesting to test those again if they are read now.</div><div><br></div><=
div>Robert</div><div><br></div><div><br></div><div><br></div></div></div>

</div>

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