Twitch stream stutters on key frames when using H264 main profile with Safari.

[finnvoor]

Observed behavior

When using the recommended Twitch settings of:

• 4,500kbps bitrate
• 1920x1080 video
• kVTProfileLevel_H264_Main_AutoLevel

The stream stutters every 2 seconds, presumably when a key frame is sent. I'm not 100% sure, but I believe this is because the video encoder takes longer to encode the key frames, and P frames are sent before the key frame is sent. They have correct timestamps, but it seems like Twitch doesn't like how far apart they are, and drops frames. Streaming with the exact same settings to YouTube works fine.

Expected behavior

The video should be smooth and not drop any frames.

To Reproduce

This can be reproduced in the iOS example project by adding:

await stream?.setVideoSettings(.init(
    videoSize: CGSize(width: 1080, height: 1920),
    bitRate: 4_500_000,
    profileLevel: kVTProfileLevel_H264_Main_AutoLevel as String
))

in the HKStreamSwitcher and commenting out the slider code where the bitrate is set. Then streaming to Twitch drops frames.

Version

2.0.3

Smartphone info.

iPhone 16 Pro
iOS 18.3

Additional context

• Default Twitch URL: rtmp://ingest.global-contribute.live-video.net/app
• Twitch EU URL: rtmp://ams02.contribute.live-video.net/app

[shogo4405]

Thank u feedback. I thought it was caused by the 2.0.0 series, but the same issue occurred in the 1.9.x series as well. Since it's the main profile, I believe it's related to the handling of compositionTimeStamp, so I'll take a look.

MAIN PROFILE

2.0.x

• 🆖 macOS + Safari
• 🆗 macOS + Chrome

1.9.x

• 🆖 macOS + Safari
• 🆗 macOS + Chrome

BASE PROFILE

1.9.x

• 🆗 macOS + Safari
• 🆗 macOS + Chrome

[finnvoor]

Great, thanks. We're currently working on implementing live streaming in the Detail iOS app and so far everything else is working great, we're testing YouTube/Instagram/LinkedIn streaming on a variety of devices. Just having some trouble with Twitch. Let us know if we can help test on any devices/platforms!

[shogo4405]

Hello, and thank you for your long-term support.

As expected, it seemed to be an issue related to the calculation of compositionTimeStamp.
I still need to conduct some more testing, but I plan to proceed in this direction.
https://github.com/shogo4405/HaishinKit.swift/pull/1680/files

[shogo4405]

I believe it was fixed in 52c707b. Please try.