fix(): framerate miscalculate fps for some codecs

[f3fora]

See https://www.ffmpeg.org/doxygen/trunk/structAVCodecContext.html

• time_base
• ticks_per_frame

[codecov[bot]]

Codecov Report

Patch coverage: 87.50% and project coverage change: +0.04 :tada:

Comparison is base (b838f9f) 79.38% compared to head (eb8deb7) 79.43%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #400 +/- ## ========================================== + Coverage 79.38% 79.43% +0.04% ========================================== Files 10 10 Lines 1276 1279 +3 ========================================== + Hits 1013 1016 +3 Misses 263 263 ``` | [Impacted Files](https://app.codecov.io/gh/JuliaIO/VideoIO.jl/pull/400?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaIO) | Coverage Δ | | |---|---|---| | [src/avio.jl](https://app.codecov.io/gh/JuliaIO/VideoIO.jl/pull/400?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaIO#diff-c3JjL2F2aW8uamw=) | `76.38% <80.00%> (ø)` | | | [src/testvideos.jl](https://app.codecov.io/gh/JuliaIO/VideoIO.jl/pull/400?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaIO#diff-c3JjL3Rlc3R2aWRlb3Muamw=) | `77.77% <100.00%> (+1.03%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/JuliaIO/VideoIO.jl/pull/400/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaIO)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[IanButterworth]

Thanks. Would you happen to be able to add tests for a reference online videos that previously failed?