[FFmpeg-user] Levels and Primaries
francois.visagie at gmail.com
Wed Feb 12 14:02:12 CET 2014
> -----Original Message-----
> From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-
> bounces at ffmpeg.org] On Behalf Of Andy Furniss
> Sent: 12 February 2014 13:49
> To: FFmpeg user questions
> Cc: Carl Eugen Hoyos
> Subject: Re: [FFmpeg-user] Levels and Primaries
> Carl Eugen Hoyos wrote:
> > Rio Kierkels <riokierkels <at> gmail.com> writes:
> >> Could be just my paranoia, but I always have the feeling that the
> >> decoder does some magic on the numbers or something.
> > (This may now be the terminology problem in the other direction.)
> > Concerning the decoder, I suspect that there actually is a guarantee
> > that an MPEG decoder in FFmpeg really only outputs MPEG levels (unless
> > told otherwise). But is that really your question?
> I don't think there is such a thing as MPEG levels - in my tests the mpeg
> decoder will re-produce whatever levels were input - I believe this is
> >> Which is why right now I'm also not certain what I'm looking for in
> >> the output.
> > I thought you are looking for levels from 0 to 15 and 236 to 255 (but
> > as said, I may just not understand the problem that you say don't
> > exist).
> The reason I first ever looked at this (with the code I posted) was after
> someone (retired BBC engineer, I think) said that broadcast mpeg streams
> were not strictly 16 - 235. He was right - there are over/under everywhere
> you look. This does not mean the levels are wrong, eg.
> there will be vastly more at 16 for dark scenes.
IIRC the 16 - 235 spec does allow over- and undershoots within reason.
> From a computer users point of view these will never normally be visible
> the default yuv (video level) - rgb (full range) conversion clips/clamps
> just as it should. Of course you can control the conversion if you want
> From a TV aspect - the hdmi spec has various modes including video level
> yuv - but even if you use this it still allows (and expects) over under.
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