Add support for ac3 and ec3 #37

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[ans-negi]

37

[ans-negi]

@googlebot I signed it!

[joeyparrish]

This looks good to me, but I have one question: On what did you base the bitrate choices for ac3 and ec3?

[ans-negi]

@joeyparrish Hey they were recommended bitrates at FFmpeg site , so from there I took stereo values. And I realised for Opus and aac there was a relation between stereo and surround values, so to calculate surround value for ac-3 and ec-3 I used same formula (160)*(6)/(2)(2) == 240k

[avelad]

I would like more to take the values that Apple gives for Reference in HLS. https://developer.apple.com/documentation/http_live_streaming/hls_authoring_specification_for_apple_devices

What do you think?

[joeyparrish]

@avelad, how about this: We adjust the defaults to be more similar to Apple's recommendations, and we also create a explicit bitrate config file that exactly matches what Apple suggests, including for video.

Here's a compromise between our existing values (extrapolated from Google internal recommendations) and Apple's recommendations:

Num. Channels	AAC Bitrate	Opus Bitrate	AC3 Bitrate	EAC3 Bitrate
2	128	64	192	96
6	256	128	384	192

@avelad, @ans-negi, if y'all both agree, let's use the value above as the default.

[avelad]

I agree!

[ans-negi]

@joeyparrish Yeah that makes sense, I have updated the defaults.

[joeyparrish]

Thanks for your contribution!