Find muxer options in VideoEncoder to test fragmented mp4

[Dan-Flores]

This PR adds logic to sortCodecOptions to find and set muxer options (check available options with ffmpeg -h muxer=mp4)

With these changes, we can now test that fragment related movflag options are utilized correctly.
But, without a 'streaming' video encoder, the benefits of fragmented mp4's are still not unlocked:

• Fragmented MP4s are useful because they allow the video file to be consumed before it is closed.
• However, since our encoder expects all frames to be encoded at once, the fragments are not flushed to become available to consume until the end of the encoding process, so we cannot access the video before encoding is completed.

[pytorch-bot]

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[Dan-Flores]

Without this conversion, we interpret the positive returned integer as a random low level error unrelated to the encoding process (ex. 24 raises EMFILE: too many open files). It might just be a bug in the FFmpeg implementation that we can work around.

Since FFmpeg errors are negative, I think its fine to set the status to successful here.