Update ffmpeg.go

[Joftal]

规避潜在的 panic 错误

[kira1928]

大佬看一下我的 PR ，没问题的话你 merge 一下我的 PR，然后我把咱俩的最终修改 merge 到这边的 master 如何？

[Joftal]

大佬看一下我的 PR ，没问题的话你 merge 一下我的 PR，然后我把咱俩的最终修改 merge 到这边的 master 如何？

merge了

[codecov-commenter]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (e481cc4) 38.56% compared to head (a0ea72a) 38.45%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/recorders/recorder.go	0.00%	6 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #675      +/-   ##
==========================================
- Coverage   38.56%   38.45%   -0.12%     
==========================================
  Files           8        8              
  Lines         695      697       +2     
==========================================
  Hits          268      268              
- Misses        411      413       +2     
  Partials       16       16              

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