# 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:** 8\
**Page:** 1

<div class="post-metadata">

**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:** [February 26, 2021, 3:22pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/1 "2021-02-26T15:22:58Z")

</div>

I have a talking-heads application … faces in small windows embedded in websites for personal finance, etc. I’m trying to figure out if MediaSoup is the way to go for the future.

To save client power and bandwidth, avoid spinning fans and all that, we’ve set this up to run at CIF resolution: 352x288 x 15fps (with an older way of delivering media). It simply doesn’t make sense to use higher resolutions just to scale them down to the small windows.

But, when I hack up the mediasoup\_sandbox to set those constraints for .getUserMedia(), the mediasoup / SVC system chooses a very low bandwidth and the video comes out nasty-looking.

(I’m new to SVC. It’s possible I’m thinking about this wrong in the SVC world.)

Can somebody point me in the right direction to figure out how to resolve this?

And, thanks for MediaSoup, great stuff!

---

<div class="post-metadata">

**Author:** ![ibc](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/ibc/32/1540_2.png) [@ibc](https://mediasoup.discourse.group/u/ibc)\
**Post date:** [February 26, 2021, 4:53pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/2 "2021-02-26T16:53:22Z")

</div>

Please clarify: which video codec and Producer encodings you are sending?

---

<div class="post-metadata">

**Author:** ![vpalmisano](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/vpalmisano/32/43_2.png) [@vpalmisano](https://mediasoup.discourse.group/u/vpalmisano)\
**Post date:** [February 26, 2021, 6:39pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/3 "2021-02-26T18:39:38Z")

</div>

Maybe CIF resolution is too small to use a Simulcast/SVC configuration. We need to know the encoder and the exact simulcast constraints you used.

---

<div class="post-metadata">

**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.)

---

<div class="post-metadata">

**Author:** ![ibc](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/ibc/32/1540_2.png) [@ibc](https://mediasoup.discourse.group/u/ibc)\
**Post date:** [March 8, 2021, 3:43pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/5 "2021-03-08T15:43:34Z")

</div>

If you pass low resolution constraints to gUM then the libwebrtc encoder will just generate low resolution simulcast streams. Anyway, this is how libwebrtc/Chrome/Firefox works. mediasoup does not and cannot change their behavior.

---

<div class="post-metadata">

**Author:** ![snnz](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/snnz/32/693_2.png) [@snnz](https://mediasoup.discourse.group/u/snnz)\
**Post date:** [March 8, 2021, 4:21pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/6 "2021-03-08T16:21:15Z")

</div>

> [@OllieJones](#):
>
> When I do this I get two spatial layers, based on the first two of my three constraints.

How do you know? Are you sure you actually get two streams or one, not 3?

---

<div class="post-metadata">

**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 18, 2021, 1:07pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/7 "2021-03-18T13:07:15Z")

</div>

I know I have more than one layer because I get layer-change events and I sometimes see the low-res layer (it’s hard to miss, it’s so ugly). I don’t believe I have the high-resolution layer because I never see it decoded

---

<div class="post-metadata">

**Author:** ![vpalmisano](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/vpalmisano/32/43_2.png) [@vpalmisano](https://mediasoup.discourse.group/u/vpalmisano)\
**Post date:** [March 18, 2021, 2:12pm UTC](https://mediasoup.discourse.group/t/talking-heads-application-352x288-strange-scalable-video-coding/2511/8 "2021-03-18T14:12:23Z")

</div>

This could help you: [media/engine/simulcast.cc - external/webrtc - Git at Google](https://chromium.googlesource.com/external/webrtc/+/master/media/engine/simulcast.cc#90)