Fixed ffmpeg-send memory leak + glitches + frame duration

[asticode]

Hey @Sean-Der,

A user of https://github.com/asticode/go-astiav has reported a memory leak and glitches in this example therefore I took the liberty to submit a PR fixing those problems. Here's what I've added:

• memory leak: unreferencing decodePacket before each inputFormatContext.ReadFrame() fixes the issue although it's weird to have to do that. My guess is that lavfi has a very specific behavior having a complex filter under the hood
• glitches: I've added proper encoder parameters to disable B frames since they don't seem to be handled by webrtc
• frame duration computation: I've also updated the frame duration computation since its value was incorrect and since we can compute it automatically based on the videoFrame's average framerate

Cheers

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (f07d02b) to head (49e921a).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #272     +/-   ##
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  Coverage    0.00%   0.00%             
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  Files          25       8     -17     
  Lines        2825     378   -2447     
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+ Misses       2825     378   -2447     

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[Sean-Der]

Amazing! Thank you so much @asticode, sorry about bad examples causing issues for your users :(

[asticode]

sorry about bad examples causing issues for your users :(

No worries, examples in my repo have the same problems so I'm the root cause of all this 😱