On Sun, 2010-11-14 at 20:01 -0500, Monty Montgomery wrote:
> The problem with MJPEG is that it uses a different color space than
> all other video formats, and the conversion isn't lossless. Going
> from any of the MPEG formats to MJPEG increases banding and
> quantization noise, and it is noticable. Every conversion from one
> format to another, even the uncompressed formats, is doing lossy
> colorspace conversion. You lose a fraction of a bit (out of only
> eight bits!) on every colorspace conversion.
>
> That doesn't even get into the fact that converting from lossy format
> to lossy format is also adding quantization noise and losing detail
> because each conversion is... well... lossy. There's no consumer
> camera out there using a bitrate high enough to be completely
> transparent as it is, and now conversion... plus conversion... plus
> conversion... each genration is losing more and more.
>
> Oh, and Cinelerra's colorspace conversion code is also subtly wrong at
> practically every step, so you're losing more than you would be
> otherwise because of that too...
Monty,
So, I'm guessing the takeaways of your discussion are:
-if at all possible, avoid converting your videos to different formats
or try to keep the conversions to a minimum
-if you do convert, stay in the same colorspace as the original footage
I understand those points. But I have a further question. As you know,
I'm using Canon 5D footage. In order to get it into Cinelerra, I've
been converting the original H264 footage via a number of steps:
-ffmpeg yuv4mpegpipe through to an mpeg2video stream via mpeg2enc
-render out audio via ffmpeg
-mux the two streams with mplex into an MPEG-PS
-import the PS into Cinelerra Monty and edit
-final output will be rendered to various formats:
-h264 via ffmpeg, two pass encode
-hdv via a similar ffmpeg yuv4mpegipe/mpeg2enc render
This strategy seems to yield decent quality material. But in your work
with Cinelerra, specifically:
1) Given unlimited disk, would you recommend a different intermediate
format for higher quality, rather than the MPEG-PS?
2) Would your recommendation change if I had limited disk space to store
intermediates?
scott
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