Add custom ETA calculation

[alexheretic]

Current eta provided by upstream indicatif has issues with slow ticks of some encode jobs. It also struggles with switching between different rates of encoding and VMAF part of a single job.

A custom eta calculation tailored for ab-av1 usage may do better.

[alexheretic]

One workaround could be to increase granularity from using encoding progress seconds / total_seconds to µs / total_µs to provide the upstream algorithm more regular integer progress.

[alexheretic]

#175 improves some scenarios but I can still see it eta rocketing up to years when it should be minutes.

[zedstate]

Why not base the ETA on frames per second?

[alexheretic]

Why not base the ETA on frames per second?

Indeed. Currently we use upstream eta calc based on progress bar updates. So yes replacing that with a custom calculation we can base it on ffmpeg reported rate. We can also account for vmaf rate & encoding rate in crf-searches.