# Talking heads application, 352x288, strange scalable video coding

**URL:** <https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511>\
**Category:** mediasoup libraries\
**Created:** [February 26, 2021, 3:22pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511 "2021-02-26T15:22:58Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![OllieJones](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/olliejones/32/850_2.png) [@OllieJones](https://mediasoup.discourse.group/u/OllieJones)\
**Post date:** [March 8, 2021, 3:23pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/4 "2021-03-08T15:23:25Z")

</div>

Please excuse the slow response to your questions. I want to make sure I have a clue what I’m talking about before answering.

My requirement is low-res talking heads, with manageable bandwidth for mobile. I have something working the way I want it to. But I don’t understand why it works. It is a kludge. I appreciate any wisdom you can share about this.

I use these three encodings

```auto
  const encodings = [
      { maxBitrate: 128000, scaleResolutionDownBy: 4 },
      { maxBitrate: 384000, scaleResolutionDownBy: 2 },
      { maxBitrate: 512000, scaleResolutionDownBy: 1 } ]

```

And these constraints

```auto
  const userMediaConstraints = {
    video: { width: { ideal: 704 }, height: { ideal: 576 },
                 frameRate: { min: 10, ideal: 15, max: 15 } },
    audio: true }

```

When I do this I get two spatial layers, based on the first two of my three constraints. For the higher resolution spatial layer he decoded / displayed videoWidth and videoHeight (on the `<video>` element) are 352x288, the `scaleResolutionDownBy=2` value. This works this way on iOS Safari and on Windows Chrome, Edgium, and Firefox.

Why does this work this way? Why can I not use just two `encodings` and gUM constraints of 352x288. When I do that I only get one spatial layer. Again, I seek understanding.

(I only use one video codec, h.264 Constrained Baseline Profile, `42e01f`. FIrefox only accepts that profile.)

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