[FFmpeg-user] Basic Video Manipulation Qustions

[pehache]

Le 27/10/2022 à 17:46, John Van Ostrand a écrit :
> Hi All,
> 
> The RAW video discussion had me thinking about resolution and bit rates for
> video and I had some questions. These are not how-to questions but general
> video questions. I'm an amateur so the contest of these questions is around
> video for home movies and social media, stored and shared as data files,
> and displayed on computers, tablets, and TVs.
> 
> 1. Why does it make sense to convert from a lossy format to raw? You're not
> gaining any more detail.

It can make sense for processing purpose

> 
> 2. Does re-rendering video over and over at the same resolution, frame
> rate, and bit rate cause degradation? For example, if I want to make
> several changes to the video, like colour correction, splicing out
> sections, transitions, titling, etc. should I be trying to do that all in
> one command?

decompressing/recompressing with the exact same codec and exact same 
encoding parameters, and without making any change on the video, should 
not cause significant degradations. In all others cases degradations are 
possible.


> 3. I understand that -c copy is a great way to eliminate time and preserve
> detail but what's the best way to do this when converting from one codec to
> another, or when performing editing or other changes?

If the source had been encoded with a very high quality (say 
"transparent", or nearly), then you can consider if was like 
uncompressed. Then you can choose whatever quality you want on output.

Otherwise, if you want to maintain quality as far as possible, it's 
better to choose a slightly higher output quality than the one of the 
source video.

> 
> 4. How important is it to keep standard resolutions, frame rates, and bit
> rates? Do hardware decoders do better with those? Do software decoders
> handle weird resolutions better?  Will strange decoding artifacts appear
> more often with non-standard parameters?

This is a much too general question...

Some mobile and low power devices have restrictions, but rather linked 
to the power needed to decode the streams.