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Transcoding Voodoo

M

mstrong

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So, I have a question. How does transcoding work?

When I convert a video file from it's native ISO (video stream VC1 and Audio TrueHD) to H265, how does it work? If the CPU usage isn't at 100% am I loosing quality? If I use my computer for other things and therefore use CPU, am I losing quality. In other words, I am assuming that the transcoding is not the same as capturing a stream of video from Netflix (via PlayOn for example) but more of a frame by frame capture of data. Or a manipulation of the ones and zeros that is dependent upon CPU usage (other than speed). Is this correct?

Also, what are the benefits of H265 over H264? My understanding is the only difference between the too is that I will get a smaller file with H265. In other words, if I encode a video as both H264 and H265, the H264 will be larger than the H265 but everything else will be the same - no difference in quality. The reason I ask is that H265 is not supported by all players and I just transcoded a movie into H265 and it took 9 hours on a Core i7 3.0 GHz with 16 GB of RAM. Clone BD predicts only 45 minutes for H264. I have lots of videos to transcode and a small increase in files size is worth the faster transcoding time.
 
H265 when done right can produce a file upto 5x smaller at the same properties as H264. That's pretty much it, but it requires a very powerful system to do with very good hw acceleration. Your i7 may not be strong enough to do it in less than 9 hours. H264 on the other hand is widely supported among CPU's and GPU's and this less time.
 
My file was about the same size as the original ISO. It doesn't appear to give me much bang for the increased transcoding time. Thoughts?
 
not really, i'm not very savvy into the technical details sorry.
 
Can anyone else answer the more technical side of my first post?
 
Google can :p

Sent from my Nexus 6P with Tapatalk
 
I am hoping for answers specific to CloneBD. :)
 
mstrong said:
When I convert a video file from it's native ISO (video stream VC1 and Audio TrueHD) to H265, how does it work?
Click to expand...

CloneBD reads the source, decodes it frame by frame and then reencodes the raw pictures using the selected codec/bitrate

mstrong said:
If the CPU usage isn't at 100% am I loosing quality?
Click to expand...
Nope. The quality is only defined by codec and bitrate.
If the CPU isn't at 100%, something is holding it back - usually the source delivers the video too slow or the destination drive can't take the result fast enough, so the CPU gets bored.

EXCEPT: if you're using nVidia hardware acceleration. Then the graphics adapter is doing all the hard work and the CPU - again - is bored.

mstrong said:
I just transcoded a movie into H265 and it took 9 hours on a Core i7 3.0 GHz with 16 GB of RAM.
Click to expand...
The speed depends severely on the quality settings (settings/video).
h265 is insanely CPU hungry when setting higher quality levels. The actual quality difference is not so huge - more noticeable on very low bitrates.

An nVidia card that supports HEVC (I believe anything from GeForce 9xx up) handles a full disc in less than an hour.

mstrong said:
If I use my computer for other things and therefore use CPU, am I losing quality.
Click to expand...
No. CloneBD runs its threads with low priority, meaning - whatever application requires the CPU will get it and CloneBD will step back for that.
That only affects the duration of the operation, nothing else. And only if those other applications really require CPU - the usual things you do, like word processing, internet, etc.... won't interfere at all.
Absolutely no harm in using your computer normally while CloneBD is processing.

mstrong said:
Also, what are the benefits of H265 over H264?
Click to expand...
A h.265 video can be roughly 50-65% the size of an h.264 video with similar quality (the "up to 5x" mentioned above, I assume, is a typo).

mstrong said:
My understanding is the only difference between the too is that I will get a smaller file with H265.
Click to expand...
Yes. And as you said: not all players support it (yet), though with 4K becoming more popular, h.265 is too.
 
As I understand it with CloneBD you tell it how big you want the output file so just changing the encoding setting from H.264 to H.265 will not produce a smaller file, rather a higher quality file. If you want a smaller file of around the same quality you not only need to change from H.264 to H.265 but also to tell it that you want a file that's about half the size of the one you got with H.264.

Please correct me if I'm wrong.
 
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