Relation of bitrate ,preset ,1 pass and 2 pass explain anyone?

[Anonymous543]

if i encode a video with this settings
-vf scale=426:240
-c:v libx264
-preset placebo
-b:v 200k

then video quality will look good

but if i use ultrafast preset instead of placebo then my encoding time will be decrease and also quality will decrease at same bitrate(200k)

Question 1. if i increase the bitrate to 1000k and change preset to ultrafast then resulting output quality will be good as placeboo with 200k bitrate?

Question 2. two pass is better over 1 pass at low bitrates i guess, but if we encode a video with 2 pass 200k bitrate and encode the same video with 1 pass and 1000k and compare both then which one will give better results??

[Anonymous543]

No answers yet.

[Sharc]

Answer 1: Depends a lot on the nature of the of the video: static/low motion, dynamic/high motion, noise, details etc. Imagine to encode a uniform black picture vs a waterfall with trees and moving leaves.

Answer 2: Same a s 1. For natural video I would say that 1 pass @ 1000k looks better.

Why don't you just try yourself?

[Anonymous543]

i watched this video
https://youtu.be/AhdbbJpl_n4

from this video i can say(idk am correct or not) if we choose any faster preset then video quality at higher bitrate will look ok
but same video at faster preset and low bitrate then video quality will be low

so i did some experiments i encoded one video at 1000k with ultrafast preset and veryslow preset
and checked output media info..
ultrafast settings was profile - constrained baseline ,cabac - no
veryslow settings was profile - high , cabac - yes



soo....if i increase bitrate then can i get the same quality of high profile and cabac enabled at constrained baseline profile and cabac disabled

i need good explaination!!

[Sharc]

Simply said, a faster preset will require a higher bitrate for a certain visual quality. You gain encoding speed and pay with bitrate (= larger file size = less compression)
A slower preset will require less bitrate for the same visual quality. You get smaller files (=lower bitrate=higher compression) and pay with encoding time

If you want to compare the quality for various settings you should compare at the same bitrate (=same file size).

Have fun with your studies and encoding experiments

[Cornucopia]

And remember, a speed preset is a Macro-preset. IOW, it is a preset that sets multiple other presets, so is not so easy to isolate variables.

In general, GIVEN THE SAME settings for everything else (hard to do wiith speed presets), a faster preset will look worse than a slower preset. But, how much worse is subjective. Very likely the worsening is more noticeable at low bitrates compared to higher bitrates.

Scott

[Anonymous543]

i did some experiments and found that we can still get good close to lossless quality at ultrafast preset with high bitrates

my first encode was ultrafast 260k with resolution 426x240 its quality look bad
in second encode i increased bitrate to 2600k and its quality was too good


so may be 260k bitrate will suitable for placeboo or veryslow presets which increases encoding time to 10x also but also increases video quality

and for ultrafast preset we get 10x encoding speed but to preserve quality we should also increase bitrates to 10x

[Anonymous543]

And remember, a speed preset is a Macro-preset. IOW, it is a preset that sets multiple other presets, so is not so easy to isolate variables.

never heared about macro preset ,which encoder includes that preset?

[Sharc]

i did some experiments and found that we can still get good close to lossless quality at ultrafast preset with high bitrates

No surprise. With sufficiently high bitrates even a lousy encoder can produce good results. Your price is file size i.e. storage space.

[pandy]

And remember, a speed preset is a Macro-preset. IOW, it is a preset that sets multiple other presets, so is not so easy to isolate variables.

never heared about macro preset ,which encoder includes that preset?

many encoders use presets for example x264 and similar but also ffmpeg use presets albeit ffmpeg presets are not the same as presets for x264

for x264 check http://dev.beandog.org/x264_preset_reference.html

and ffmpeg presets for libx264 re for example here:
https://github.com/waseem/ffmpeg-libx264-presets

compare both to get a grip how presets can store common parameters so no need to call them every time (but still invoking preset you may alter some for the settings if you will) - preset can be compared to the cookbook...

btw extreme case for bitrate vs quality are so called Intra codecs used usually where time not the bandwidth is critical (frequently they are used by video cameras).