Prores ffmpeg questions I am trying to understand how to use Prores Kostya with FFmpeg, and I have a few questions regarding this:


I have a Panasonic G85 and Gopro Hero 7 black which I used to shoot 4k in.  For 4k footage, the Panasonic records at 4:2:0 8-bit at 100 Mbps, and the Gopro 8 bit 4:2:0 at 78 Mbps.  With this in mind is there any point in selecting a Prores profile other than ProRes 422 LT?  The reason I say this is because the LT profile has 102 Mb/s, which exceeds the source footage from both cameras. 
I have read that the qscale command is not needed, and a user can just select a profile which will define a standard bit rate (for LT this is 102  Mb/s). I have seen people saying that ProRes is a profile-based codec, meaning that when you select one of the profiles, it does a fixed amount of compression, defined in the spec. If you want a different compression level, you're supposed to choose a different profile, rather than change a quality setting with the qscale command, as this may result in a violation of the standard, and have the potential to cause playback issues (particularly with hardware decoders).  So with this in mind is it better to miss out the qscale command?
Why is it necessary to specify the -pix_fmt, as I thought all the 422 profiles defaulted to yuv422p10le and all the  4444 profiles defaulted to yuv4444p10le. So why is there a need to specify this value?
1) your Panasonic footage will be H.264; GoPro may be H.264 or H.265. These are inter-frame codecs whereas ProRes is an intra-frame codec (each frame is coded standalone and doesn't depend on other frames for decoding). So, you should consider a higher bitrate to maintain source quality.

2) FFmpeg does allow you to set a custom quantizer but by default it will use a fixed quality setting per profile. For custom quant, use -global_quality N.

3) FFmpeg has to convert to the given pixel format which is what output -pix_fmt will do. The encoder only encodes i.e. takes in raw uncompressed input frames and delivers coded data.