You need to understand the way the different codecs work and why they are used. ProRes 4444 is an archival intermediate codec... it is intended for preserving the absolute maximum amount of detail possible in video files up to 12 bit color depth, with the bare minimum of compression applied. The intended target is for other editors, colorists, and visual effects artists to be able to work on the file with minimal quality loss, and have plenty of quality there needed for high quality chroma keying, color grading, etc.

Magix AVC/HEVC are delivery formats. They are intended for the end user, and have been compressed much more than the ProRes files have... so much that if you tried to do chroma keying or color grading using those files, the end result would be inferior to if you used ProRes, but the file size is reasonable enough to be easily stored or streamed over the internet.

Even for things like color grading, ProRes 4444 is too high quality and too large of a file size... too large to even play back smoothly on most hard drives... you typically only want to use it for visual effects work where they need every bit of quality you can possibly give them. It supports alpha channels, which are very useful for vfx artists, as they allow perfect transparency when overlaying it over other videos.

A 5 second video rendered in Vegas using native ProRes 444 format with alpha channel is 1.08GB. The total bitrate is 1,866,118 kbps. Is such a high bitrate really necessary that generates such a large file?

Apple site says

• Apple ProRes 4444 is a high-quality solution for storing and exchanging motion graphics and composites, with excellent multigeneration performance and a mathematically lossless alpha channel of up to 16 bits. This codec features a remarkably low data rate compared to uncompressed 4:4:4 HD. It has a target data rate of approximately 330 Mbps for 4:4:4 sources at 1920x1080 and 29.97 fps.
• Apple ProRes 4444 XQ features a target data rate of approximately 500 Mbps for 4:4:4 sources at 1920x1080 and 29.97 fps.

https://support.apple.com/en-us/HT202410

At 4444 the maximum bitrate with alpha channel I could obtain is 331mbit/s with Premiere Pro, which is spot on with the apple spec of 330mbit/s. I used these settings

Media info for Vegas

• Format                                   : QuickTime
• Format/Info                              : Original Apple specifications
• File size                                : 1.09 GiB
• Duration                                 : 5 s 5 ms
• Overall bit rate mode                    : Constant
• Overall bit rate                         : 1 864 Mb/s
• Writing library                          : Apple QuickTime
• Video
• ID                                       : 1
• Format                                   : ProRes
• Format version                           : Version 1
• Format profile                           : 4444
• Codec ID                                 : ap4h
• Duration                                 : 5 s 5 ms
• Bit rate mode                            : Constant
• Bit rate                                 : 1 863 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                              : YUVA
• Chroma subsampling                       : 4:4:4
• Scan type                                : Progressive
• Bits/(Pixel*Frame)                       : 29.973
• Stream size                              : 1.09 GiB (100%)
• Writing library                          : magx
• Color primaries                          : BT.709
• Transfer characteristics                 : BT.709
• Matrix coefficients                      : BT.709
•  

Media info for Premiere

• Format                                   : MPEG-4
• Format profile                           : QuickTime
• Codec ID                                 : qt   2005.03 (qt  )
• File size                                : 199 MiB
• Duration                                 : 5 s 0 ms
• Overall bit rate mode                    : Variable
• Overall bit rate                         : 334 Mb/s
• Writing library                          : Apple QuickTime
• TIM                                      : 00:00:00:00
• TSC                                      : 2997
• TSZ                                      : 100
• Video
• ID                                       : 1
• Format                                   : ProRes
• Format version                           : Version 1
• Format profile                           : 4444
• Codec ID                                 : ap4h
• Duration                                 : 5 s 0 ms
• Bit rate mode                            : Variable
• Bit rate                                 : 331 Mb/s
• Width                                    : 1 920 pixels
• Height                                   : 1 080 pixels
• Display aspect ratio                     : 16:9
• Frame rate mode                          : Constant
• Frame rate                               : 30.000 FPS
• Color space                              : YUVA
• Chroma subsampling                       : 4:4:4
• Scan type                                : Progressive
• Bits/(Pixel*Frame)                       : 5.323
• Stream size                              : 197 MiB (99%)
• Writing library                          : adb0
• Color primaries                          : BT.709
• Transfer characteristics                 : BT.709
• Matrix coefficients                      : BT.709

Interesting that Premiere gets the data rate and format wrong.

What is your Vegas version and build number? @Jeditpro

@Former user Your information cleared my doubts and confirmed my suspicions. Thanks!

@Musicvid I use VP19 Build 458. But the same occur in all Builds of VP19 and in new Version 20.

@Jeditpro Yes, both 4444 codecs break with adding alpha channel. Most of the prores options are out of spec, not giving correct bitrate, also, Prores is a variable bitrate format, but on Vegas it's CBR only. It is possible to force CBR on some NLE's but the default is VBR