vp8enc: better defaults, more presets/profiles
Submitted by Tim Müller
Just some quick comments on our default values from an e-mail exchange with Ronald:
mode : Mode
Enum "GstVP8EncMode" Default: 0, "vbr"
(0): vbr - Variable Bit Rate (VBR) mode
(1): cbr - Constant Bit Rate (CBR) mode
You may want to look into CQ mode (2) also.
max-keyframe-distance: Maximum distance between key frames
Integer. Range: 0 - 9999 Default: 60
60 is quite low (for high-quality encodes), any particular reason for that?
I think in our tests and on webmproject.org, we recommend 120 frames
as kf interval.
multipass-mode : Multipass encode mode
Enum "GstVP8EncMultipassMode" Default: 0, "one-pass"
(0): one-pass - One pass encoding (default)
(1): first-pass - First pass of multipass encoding
(2): last-pass - Last pass of multipass encoding
Can the default be changes to 2pass? We really do all our internal
testing for high-quality encodes on 2pass, it'll generate much better
output (in the range of >1dB difference).
(tpm: can't ever default to 2-pass, since that requires co-operation by the application. 2-pass can only ever be opt-in)
auto-alt-ref-frames : Automatically create alternative
Boolean. Default: false
This isn't a good idea, alt-refs by themselves will also cause several
tenths of dB difference (in a positive way), I'd highly recommend you
turn them on for high-quality (2pass) encodes.
(tpm: only for high-quality 2-pass encodes? BBB: yes)
lag-in-frames : If set, this value allows the encoder to consume
a number of input frames before producing output frames.
Unsigned Integer. Range: 0 - 64 Default: 0
Probably want to up this to e.g. 25 for high-quality encodes (unless 0
means 'don't touch').
(tpm: I think 0 means whatever the library default is, someone needs to check this)
tune : Tune
Enum "GstVP8EncTune" Default: 0, "psnr"
(0): psnr - Tune for PSNR
(1): ssim - Tune for SSIM
Minor nit, most people would claim ssim is a better default here, but
it's not that relevant.
I see you haven't mapped the ARNR options, which provide a quality
boost for noisy input (without affecting noiseless input much), are
you guys interested in exposing these options also? They affect the
way the alt-ref frame is used.
(tpm: might be good for input from webcams - though what would be even better if we could detect that kind of input and switch to that mode automatically)
Other possibly interesting pages: