På Tue, 10 Jul 2012 21:10:38 +0200, skrev Nicolas Ecarnot <nico...@ecarnot.net>:
Le 28/06/2012 12:11, Nicolas Ecarnot a écrit :
Hi,
Following the advices here :
http://www.g-raffa.eu/Cinelerra/HOWTO/get_media_ready.html
I'm converting with ffmpeg / avconv my input media files to MJPEG files.
No obvious quality loss occurs, but they result in darker videos - dark
enough to be noticed. In fact, they are getting darker and/or more
contrasted.
...
But when I'm converting, here is what I notice in avconv/ffmpeg output:
> Incompatible pixel format 'yuv420p' for codec 'mjpeg', auto-selecting
format 'yuvj420p'
This happens only on video that have this yuv420p pix format.
How do I have to understand that?
...
I'm sorry to insist on that point, but according to every doc I read
related to cinelerra, everyone seems to advice to convert to MJPEG.
This format sounds great to nle software, but I can't figure it out how
I can manage this contrast problem.
I'm not clear about whether the fault is on my source files, or a
limitation of the MJPEG format, or a limitation of the converter
(ffmpeg/avconv).
I'm sure many of you have a well established workflow and you can't live
with this issue, so maybe your video source formats don't bother you the
way I'm bothered...
It does bother me, for what it is worth. I think the problem is due to
different luma range (MJPEG is full range; 0-255) and chroma sample alignment.
I'd guess that the contrast range is first stretched, then truncated, leading
to higher contrast _and_ some crushed blacks and clipped highlights.
What to do? Find some other intermediate or proxy format. I'd suggest
DNxHD for intermediates and intra-only low-bitrate h.264 for proxies.
--
Herman Robak
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