Implement forced keyframes for x264

[zjzhang-cn]

Description

 实现x264的强制关键帧方法

Reference issue

Fixes #...

[codecov]

Codecov Report

Merging #388 (7d0e84f) into master (548cdac) will decrease coverage by 0.05%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #388      +/-   ##
==========================================
- Coverage   47.16%   47.11%   -0.06%     
==========================================
  Files          67       67              
  Lines        4380     4387       +7     
==========================================
+ Hits         2066     2067       +1     
- Misses       2189     2195       +6     
  Partials      125      125              

Impacted Files	Coverage Δ
pkg/codec/x264/x264.go	63.95% <0.00%> (-0.76%)	⬇️
pkg/driver/camera/camera_linux.go	26.31% <0.00%> (-0.80%)	⬇️
pkg/prop/prop.go	72.10% <0.00%> (+0.19%)	⬆️

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[at-wat]

LGTM