is there anything fast first pass and slow first pass?

[Anonymous543]

[Attachment 63029 - Click to enlarge]

is there anything fast first pass and slow first pass?
if yes then whats thier advantages and disadvantages?

[Selur]

Using a slower first pass means that a more accurate 1st pass will be used.
Depending on the encoder and content this might have small benifits in regard of compression ration.

[Anonymous543]

Using a slower first pass means that a more accurate 1st pass will be used.
Depending on the encoder and content this might have small benifits in regard of compression ration.

do you know how i can enable slow first pass in ffmpeg while using x265?

[Selur]

iirc. it should work with:

--x265-params pass=1:slow-firstpass=1

[Anonymous543]

iirc. it should work with:

--x265-params pass=1:slow-firstpass=1

for simplicity if i chose placebo preset then will it automatically turn on slow first pass? just like x264?

[Selur]

Unlike x264, in x265 the default is to use a fast 1st pass, so: no

[Anonymous543]

ohh thanks for info

[Anonymous543]

btw slow first pass vs. fast first pass which will give better video quality?

[Selur]

slow first pass is more precise and could potentially preserve more details from the source, whether it does or is just a waste of time depends on your source and your settings,....

[Anonymous543]

slow first pass is more precise and could potentially preserve more details from the source, whether it does or is just a waste of time depends on your source and your settings,....

which media encoder you use? or you will recommend?

[Selur]

I'm probably not the right person to ask, but with the knowledge you seem to have, you might want to use Handbrake, VidCoder, may be StaxRip or MeGui if you read up a lot.

[Anonymous543]

I'm probably not the right person to ask, but with the knowledge you seem to have, you might want to use Handbrake, VidCoder, may be StaxRip or MeGui if you read up a lot.

I tried one before it was avidemux I liked that one to encode videos but it's reviews are bad idk why people doesn't like avidemux

[Selur]

Nothing wrong with avidemux, doesn't support Avisnth/Vapoursynth, but other than that solid tool in my book,..

[Anonymous543]

Nothing wrong with avidemux, doesn't support Avisnth/Vapoursynth, but other than that solid tool in my book,..

What is avisnth/vapoursynth?

[Selur]

Skript based frame works for filtering content.

[Anonymous543]

Skript based frame works for filtering content.

Thanks for info ✨

[Anonymous543]

iirc. it should work with:

--x265-params pass=1:slow-firstpass=1

in ffmpeg how can i see which default settings are getting used for libx265 encoder
because i think by default it uses slow firstpass

[Selur]

Ah, I mixed it up before.
x264 uses fast first by default and x265 doesn't.
To know for sure you need to look at the source code in ffmpeg.

[Anonymous543]

Ah, I mixed it up before.
x264 uses fast first by default and x265 doesn't.
To know for sure you need to look at the source code in ffmpeg.

i dont understand coding and all can you look in to that and tell me libx265 it uses slow first pass or fast first pass by default
or may be some one else

[Selur]

There is a simply way to know: try whether pass=1low-firstpass=1 slows things down or not,...

[Anonymous543]

There is a simply way to know: try whether pass=1low-firstpass=1 slows things down or not,...

ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset ultrafast -x265-params pass=1 -f null NUL && ^
ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset ultrafast -x265-params pass=1:slow-firstpass=1 -f null NUL && ^
ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset ultrafast -x265-params pass=1:slow-firstpass=0 -f null NUL && ^

tried, but its hard to tell because input video length was 30 secs thats why encoding time diffrences is in miliseconds and everytime it gives diffrent time diffrencess

[Selur]

to state the obvious: Why not simply use a longer souce? (at least I don't plan to spend time searching through ffmpegs source code to varify something that you can easily test)

[jagabo]

Send the first pass video output to a file rather than NUL. Then you can see all the encoding parameters with MediaInfo.

And using the ultrafast preset to check this makes no sense.

[Anonymous543]

soo... i changed preset to slow and results are.....

ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset slow -x265-params pass=1 -f null NUL && ^

without specifying anything ,takes 88.19seconds for 1st pass

ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset slow -x265-params pass=1:slow-firstpass=1 -f null NUL && ^

with specifying -x265-params pass=1:slow-firstpass=1 takes 87.58seconds for 1st pass

ffmpeg -y -i input.mp4 -c:v libx265 -b:v 100k -preset slow -x265-params pass=1:slow-firstpass=0 -f null NUL && ^

with specifying -x265-params pass=1:slow-firstpass=0 takes 22.06seconds for 1st pass



looks like slow first pass is enabled by default for ffmpeg libx265(hevc) but still for confirmation i'll make one more thread on it.

[Anonymous543]

Unlike x264, in x265 the default is to use a fast 1st pass, so: no

i think x265 the default is to use slow 1st pass

[Selur]

x264 uses fast first by default and x265 doesn't.

That is what I wrote after that statement you quoted,....

[Anonymous543]

x264 uses fast first by default and x265 doesn't.

That is what I wrote after that statement you quoted,....

So do you know what defaults ffmpeg x265 uses for 1st pass?
Am a bit more intrested in ffmpeg x265

[Selur]

https://x265.readthedocs.io/en/master/presets.html with preset medium shows the defaults that are directly changed through presets.
Looking through the option https://x265.readthedocs.io/en/master/cli.html you can also see for each option it's default value.
Also like jagabo mentioned you could also simple do a encode and look at the output with MediaInfo to see the settings that were used,...

Cu Selur

Ps.: this seems to be going in circles, I'm off this thread, but I wish you luck in your endevours.

[jagabo]

So do you know what defaults ffmpeg x265 uses for 1st pass?

You could just read the docs:
https://x265.readthedocs.io/en/master/cli.html?highlight=slow-first-pass#cmdoption-slow-firstpass

[Anonymous543]

Damm it was in documentation , and i was just wasting my time in doing weird tests and all ,anyways thank you selur and jagabo