MP4 output from Elastic Transcoder needs to be updated

[collinpreston]

Steps to Reproduce

1. Create or use an existing collection in OVS that is associated with a course on edX.
2. Upload a video to the collection.
3. Attempt to download the video either from s3 (https://s3.console.aws.amazon.com/s3/buckets/odl-video-service-transcoded-rc?prefix=transcoded/&region=us-east-1) or by adding the video ID to a course component and specifying "user can download" from the advanced video settings (instructions for this are explained here: Mp4 video download #1011).

Expected Behavior

1. The downloaded mp4 video should have the following details:

• 320 kbps
• 48 kHz audio

Actual Behavior

View the mp4 video's codec settings are slightly different.

Additional information

1. The Elastic Encoder preset for mp4 files is defined here: https://github.com/mitodl/odl-video-service/blob/f89d0de9ec3893d2502c4069e4409bdd4cde3357/config/et_mp4_preset.json

[pdpinch]

I believe @collinpreston already fixed this in production, but it needs to be tested.