Add support for ac3 and ec3 #37

[ans-negi]

No description provided.

[google-cla]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

ℹ️ Googlers: Go here for more info.

[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!