How can I get a Prores LT file accordingly to Prores LT on Atomos Ninja2

[Karl]

Hello,
I’m recording in Prores LT on Atomos Ninja 2.
After exporting file from Shotcut with ‘vprofile=1’ back to Prores LT I get a higher bitrate than before.
What options I’ve to change in export to get identical compression?

Thanks for answering, Karl

Ninja file data are:

Video
ID : 2
Format : ProRes
Format version : Version 0
Format profile : 422 LT
Codec ID : apcs
Duration : 1 min 2 s
Bit rate mode : Variable
Bit rate : 85.0 Mb/s
Width : 1 920 pixels
Clean aperture width : 1 888 pixels
Height : 1 080 pixels
Clean aperture height : 1 062 pixels
Display aspect ratio : 16:9
Clean aperture display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 29.970 (30000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:2
Scan type : Progressive
Bits/(Pixel*Frame) : 1.368
Stream size : 638 MiB (98%)
Writing library : atms
Language : English
Encoded date : UTC 2020-11-20 17:14:55
Tagged date : UTC 2020-11-20 17:14:55
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 1
Format : PCM
Format settings : Little / Signed
Format settings, Endianness : Little
Format settings, Sign : Signed
Codec ID : sowt
Duration : 1 min 2 s
Bit rate mode : Constant
Bit rate : 1 536 kb/s
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 kHz
Bit depth : 16 bits
Stream size : 5.77 MiB (1%)
Language : English
Encoded date : UTC 2020-11-20 17:14:55
Tagged date : UTC 2020-11-20 17:14:55

Same File exported with vprofile=1:

Video
ID : 1
Format : ProRes
Format version : Version 0
Format profile : 422 LT
Codec ID : apcs
Duration : 1 min 2 s
Bit rate mode : Variable
Bit rate : 230 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 29.970 (30000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:2
Scan type : Progressive
Bits/(Pixel*Frame) : 3.701
Stream size : 1.69 GiB (99%)
Writing library : Apple
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 2
Format : PCM
Format settings : Little / Signed
Format settings, Endianness : Little
Format settings, Sign : Signed
Codec ID : sowt
Duration : 1 min 2 s
Bit rate mode : Constant
Bit rate : 1 536 kb/s
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 kHz
Bit depth : 16 bits
Stream size : 11.5 MiB (1%)
Default : Yes
Alternate group : 1

[Austin]

Did you export with prores or prores_ks as the video codec? prores doesn’t do much in the way of rate control. prores_ks is much closer to spec.

[Karl]

I used prores-ks. Modified from preset prores422.
I also tried limited bitrate set to 80M but there was no effect.

[Austin]

Odd. I trust your MediaInfo, but I am unable to reproduce a file bigger than 750 MB on a basic one minute test clip using qscale 1. Is something about your scene particularly difficult to encode? Regardless, prores_ks does respond to the qscale parameter which can be set on the Export > Codec tab. I’ve seen references saying other people have used between 5 and 15 for the LT profile. For my test clip, qscale 15 drops the file to 275 MB.

[Karl]

I left qscale on default 100% thinking that ‘vprofile=1’, automaticly leads to the correct value for Prores LT in this format.
Also I thought that 100% quality of a stream wouldn’t change the streamrate when it was 85Mbit/s before because this is default 100%. Any upsampling than would be more than it.
If qscale 100 changes up nevertheless and i’ve to adjust it for the right streamrate it seems to work independent from the switch ‘vprofile=1’ and also independent from the streamrate of the original video. What does the 100% refer to then?
The material was not processed. It was a preliminary test for future work with no changes.