Interview on Usesthis.comPosted on May 13th, 2013 7 comments
Here is an interview I did on usesthis.com:
It’s about how I do the blog and some of the tools I use, for those interested.
“They all lack a feature called Constant Quality, which changes the bitrate on a frame by frame basis based on the content in the frame. So fast-moving images take more space (less compression), and still images (like my talking head) take less space (more compression).”
Dave, you think that Handbrake really give you “Constant Quality”???
No way, Handbrake QC uses x264 CRF and CRF != QC, some info:
The final ratecontrol method: Constant Ratefactor. While qp targets a certain quantizer, and bitrate targets a certain filesize, crf targets a certain ‘quality’. The idea is for crf n to give the same perceptual quality as qp n, just in a smaller space. The arbitrary unit of measure for crf values is the “ratefactor”.
CRF achieves this by reducing the quality of ‘less important’ frames. In this context, ‘less important’ means frames in complex or high-motion scenes, where quality is either more expensive (in terms of bits) or less visible, will have their quantizer increased. The bits saved in frames like these are redistributed to frames where they will be more effective.
CRF will take less time than a 2pass bitrate encode, because the ‘first pass’ from a 2pass encode was skipped. On the other hand, it’s impossible to predict the bitrate a CRF encode will come out to. It’s up to you to decide which rate-control mode is better for your circumstances.
This option is mutually exclusive with qp and bitrate. See this writeup for more information on the various ratecontrol systems.
See also: –qp, –bitrate ”
“CRF in a nutshell
The way constant quality encoding is usually done, it keeps up a constant quality by compressing every frame of the same type the same amount. In tech speak, that’s maintaining a constant QP (quantization parameter).
Constant Rate Factor, on the other hand, will compress different frames by different amounts. It does this by taking motion into account.
The eye perceives more detail in still objects than when they’re in motion. Because of this, a video compressor can apply more compression (drop more detail) when things are moving, and apply less compression (retain more detail) when things are still. Subjectively, the video will seem to have higher quality.”
So as you can see, not every frame will have the same quality…
And yes, Handbrake really uses x264 CRF, just look at a Handbrake log:
“19:29:48] + quality: 22.00 (RF)
[19:29:49] encx264: Encoding at constant RF 22.000000″
in this example I set Handbrake->Video->Constant Quality->FR=22
“there’s no free lunches”
Sony Alpha DSLRs have full phase-detect focusing during video taking. It is the construction difference from Canon and Nikon.
Most people doesn’t know it, and not really take Sony as a real DSLR producer.
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