Issue with Keyframe Stuttering and Pixelation on iPhones with Resolutions Above 1280x720 in AntMedia

[wnwcst]

We are experiencing an issue specifically on iPhones when streaming with a resolution higher than 1280x720 in AntMedia. Every keyframe slightly stutters, and the image breaks into pixels in areas with movement.

We have already tried increasing the bitrate, bandwidth, and encoder profile, but none of these solutions have helped. It seems like the issue might be related to the iPhone's hardware encoder. We need to find a way to resolve this.

Any insights or suggestions would be greatly appreciated!

[filip-ams]

Greetings @wnwcst,

Thank you for reaching out.

Could you please provide details about how you publish/play the stream so I can try to reproduce this issue? Also sending the screenshot of your ant media application settings would help a lot. Thanks in advance!

[wnwcst]

Hi Filip!

Thanks for getting back to me. If we can solve this issue, it’ll be a huge win for us—we’ve been struggling with it for so long!

We’re publishing the stream via WebRTC to an Ant Media Server, where it’s also played back via WebRTC.

The problem happens only on iPhones when streaming above 1280x720.

Every keyframe causes a slight stutter, and the image breaks into pixels in areas with movement.
We’ve already tried tweaking bitrate, bandwidth, and encoder profile, but nothing has helped.
After a keyframe is sent, the quantization parameter (QP) spikes for about a second, causing temporary quality degradation before stabilizing.

The issue is most noticeable at 1920x1080, but it still happens (though less often) at 1280x720.
On Android devices, it either doesn’t happen at all or is way less noticeable.
Current Streaming Parameters:
Frame Rate: 30 fps
Bitrate:
1920x1080 — 7500 kbps
1280x720 — 4000 kbps
I’ve attached:
✅ Screenshots showing how the QP changes after a keyframe. On the screenshots, you can see that on Android, all P-frames have a stable and consistent size, with a steady quantization parameter. However, on iPhone, even at 720p, there are noticeable QP spikes right after an I-frame P-frames get heavily compressed, leading to image degradation after every I-frame. At 720p, the quality drop is minor but still present, while at 1080p, the quality deteriorates significantly, and the lag becomes visible to the eye. The quantization parameter rises up to 50 after an I-frame.
✅ Our Ant Media application settings.

Let me know if you need anything else. Really appreciate your help!

Android 720

Android 1080

Iphone 720

Iphone 1080

Config 720p.txt
Config 1080p.txt

By the way, I wanted to ask where I can configure the parameters that are directly passed to the encoder when starting a WebRTC stream. I’ve noticed that not all settings from the Advanced tab actually affect the encoder. For example, when I set the CRF parameter, it seems to be ignored. As I understand it, most of these settings control the encoding process within Ant Media itself, but they do not directly affect the encoder that publishes the video.

[wnwcst]

My account was blocked on Github due to config files, so I’m writing this message to remind myself)