The stereo downmix flags are hard-coded into the surround metadata. Nothing mortals can or should do to change them. I don't suggest uploading PCM to Youtube.

The stereo downmix flags are hard-coded into the surround metadata. Nothing mortals can or should do to change them. I don't suggest uploading PCM to Youtube.

Why not upload PCM audio to YouTube?

I saw that one can use an app called ffmpeg (think thats it) to mux a stereo and surround track together with the video and that YouTube will then choose to play the appropriate track. Any experience with doing that?

For YouTube, I create a separate stereo mix from the 5:1 stems (or the timeline tracks if available). When 5:1 mixes are done by inexperienced folks, the down-mix can be unusable, I have witnessed this more than a few times at film festivals and such.

For YouTube, I create a separate stereo mix from the 5:1 stems (or the timeline tracks if available). When 5:1 mixes are done by inexperienced folks, the down-mix can be unusable, I have witnessed this more than a few times at film festivals and such.

The client provided me with both 5.1 mixes and stereo mixes for this concert video. But you only recommend uploading stereo audio to YouTube? or what is the recommendation?

The stereo downmix flags are hard-coded into the surround metadata. Nothing mortals can or should do to change them. I don't suggest uploading PCM to Youtube.

So as I'm the one outputting the surround audio, don't I control what goes into it's metadata? To clarify the situation, the client provided me with separate stems for each 5.1 channel as well as a stereo file. It's a concert that I shot. I'm editing my multi-cam video together with the client-provided audio from the show and the client would love to have YouTube play the sound in surround where a user has a surround system, and in stereo (or a good stereo downmix) where they do not.

I got curious so I went to the YouTube help page, typed in "5.1 surround", and here's some of what I got.

Watch YouTube on TV with 5.1 surround sound

You can watch YouTube videos on your TV with 5.1 surround sound. Enjoy YouTube’s library of shows and movies as well as other YouTube content with your supported surround sound system.

Turn 5.1 surround sound on:

Once you select a video to play, a player control bar will show. Go to 5.1 surround sound to turn it on or off.

Note: The setting will only appear for videos and devices that support 5.1 surround sound. 5.1 in YouTube is supported on all 2021 and later TVs, Chromecast, Apple TV, Roku and most Fire TV devices. In addition, many 2020 and earlier TVs may also support surround sound - check your device manufacturer to see if your device supports 5.1 for YouTube.


Here's the recommended audio codec for upload:

Audio codec: AAC-LC

Channels: Stereo or Stereo + 5.1

Sample rate 96khz or 48khz

HTH.

Mike

I got curious so I went to the YouTube help page, typed in "5.1 surround", and here's some of what I got.

 

Watch YouTube on TV with 5.1 surround sound

You can watch YouTube videos on your TV with 5.1 surround sound. Enjoy YouTube’s library of shows and movies as well as other YouTube content with your supported surround sound system.

Turn 5.1 surround sound on:

Once you select a video to play, a player control bar will show. Go to 5.1 surround sound to turn it on or off.

Note: The setting will only appear for videos and devices that support 5.1 surround sound. 5.1 in YouTube is supported on all 2021 and later TVs, Chromecast, Apple TV, Roku and most Fire TV devices. In addition, many 2020 and earlier TVs may also support surround sound - check your device manufacturer to see if your device supports 5.1 for YouTube.


Here's the recommended audio codec for upload:

Audio codec: AAC-LC

Channels: Stereo or Stereo + 5.1

Sample rate 96khz or 48khz

 

HTH.

Mike

That's helpful ..but how does one create a video with Stereo + 5.1 surround audio out of Vegas? Do I need to use that app (ffmpeg) to mux them together? or is there an easy way within Vegas?

@tim-neighbors I've done it before, and it worked. Probably just muxed together the video + stereo + 5.1 using a freeware muxer. You could also just upload the 5.1 audio and see how YT handles the downmix. It most likely creates normal stereo tracks, and probably of an acceptable quality. If you wanted to create your own Dolby ProLogic II stereo track to expand out to 5.1 surround then that would seem to be a purpose for creating your own stereo tracks + 5.1. Hardware devices will decode E-AC3/AC3, while computer users can decode the prologic II

There's a tiny chance YT actually downmix the 5.1 to pro logic 2 encodes because I've heard they downmix Dolby Atmos to DD+ 5.1 + metadata which allows Atmos to recreate the missing channels, although Prologic has nothing to do with meta data. I don't know how to test for Prologic, I suspect it's not used unless you upload Lt/Rt instead of Lo/Ro, and maybe it shouldn't be used for YT stereo bitrates

Why not upload PCM audio to YouTube?

The potential for sync problems following Youtube processing is not worth the risk, or my time.

@tim-neighbors

"...how does one create a video with Stereo + 5.1 surround audio out of Vegas? Do I need to use that app (ffmpeg) to mux them together? or is there an easy way within Vegas?"

Voukoder will create an AVC/AAC surround file from the Vegas Pro timeline.

See this thread.

https://www.vegascreativesoftware.info/us/forum/problem-playing-rendered-video-on-samsung-qled-tv--117334/?page=2#ca864400

You could probably render the stereo file separately and mux it with Shutter Encoder.

Not really experienced with 5.1 but it looks like only a couple codecs I have in Vegas do it. Sony AVC/MVC worked up to HD. Voukoder also worked, but up to 4k. I set the Vegas project properties to 5.1 on the audio tab and Voukoder picked up on that without any other special setting in it's dialog except to choose the AAC (ffmpeg) audio codec. The Sony HD preset required selecting 5.1 on it's render template audio tab. The Magix and ProRes presets don't have a selection on their audio tabs and rendered stereo even when I set the project to 5.1. Also tried Voukoder opus but only got a single audio channel. Same with Oog vorbis. Only mention those because YouTube transcodes all my 4k uploads to vp9/opus but I've only ever sent them stereo.

Having as little experience as I do with 5.1 mixing, if someone gave me both stereo and 5.1 mixes, I'd be inclined to drop them into 2 different projects, as-is, and set the audio properties for each to match the audio tracks. If any level adjustment, compression, or limiting is called for, I'd try the Surround Sound version of Wave Hammer on the master bus. Then upload separately identified videos with cross-links in the description. But you might upload the 5.1 version 1st and let your client decide if YouTube's conversion to stereo is acceptable... if it is, their hit-count wouldn't be split.

I tested stereo + 5.1 again, and still works as expected. I have music on the stereo track, and a surround sound helicopter on 5.1. If you listen via your computer you'll only hear the music (at least I think so), but if you're viewing through a hardware device with surround you'll hear a helicopter

If you listen via your computer you'll only hear the music (at least I think so)

Yes, music only - using a digital connection to an amp with reasonably good monitor speakers. Great song BTW.

I didn't detect any helicopter audio, but if it were there, it certainly went over my head 😃😄😁🚁