On Sat, May 28, 2011 at 11:26:22AM -0700, Brian Matherly wrote:
>
>
> > Ian Lynagh <igloo <at> earth.li> writes:
> >> Besides, I'd certainly like to understand how to make lossless output,
> >> even if I decide not to in the end.
> >
> > You might want to just dump raw YUV (or RGB, or whatever colorspace
> > your source is in) frames into a quicktime container for lossless output:
> >
> > -consumer avformat target=melt.mov f=mov vcodec=rawvideo
> > pix_fmt=uyvy422 vtag=yuvs acodec=pcm_s16le
I don't expect that this will produce anything any different than using
x264. melt will presumably have already done and subsampling etc by the
time it looks at what the consumer is.
In actual fact,
melt a.mp4 -profile atsc_1080p_50 -consumer avformat target=c.mov f=mov
vcodec=rawvideo pix_fmt=uyvy422 vtag=yuvs acodec=pcm_s16le
produces a 182 byte file, and
melt a.mp4 -profile atsc_1080p_50 -consumer avformat target=c.mov f=mov
vcodec=rawvideo pix_fmt=uyvy420 vtag=yuvs acodec=pcm_s16le
segfaults.
a.mp4 is "Video: h264 (High 4:4:4 Predictive), yuv420p".
> Good call. Otherwise, you have to determine what "lossless" means to you. Any
> compression algorithm is going to lose some amount of information - no matter
> what parameters you use. True lossless really means "uncompressed".
Not so! For example, pkzip, gzip, bzip2, etc are all lossless
compression algorithms.
(although "compression algorithm" is technically a misnomer, I guess, as
on average they produce larger outputs than inputs. But we normally only
use them on inputs like English text, which are in the subset of inputs
that they make smaller. But I digress).
Thanks
Ian
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