Chrome scales up even with fixed resolution

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Carlos N

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May 15, 2019, 5:04:59 AM5/15/19

to discuss-webrtc

Hi,

We're facing issues with recording videos using WebRTC because apparently Chrome is scaling up the resolution at the beginning of the transmission.

So let's say we use constraints such as "video: width:{min:1280}, height:{min:720}", if we use VP8 codec Chrome firstly try with 640x360px, then upscale after few seconds to 960x540px and eventually to 1280x720px after more seconds (length in seconds will depend on framerate as more frames will give more congestion information). This is also true for H264 codec in Windows 7 but not in Windows 10 with H264. Also Firefox is not behaving like this.

Some screenshots:

Chrome VP8 (Windows 7 and Windows 10):

Chrome VP8 with higher framerate:

Chrome H264 Windows 7:

Chrome H264 Windows 10:

The resulting recorded video file will be 640x360px with VP8 (as there is a filter in-between that will downscale to the minimum resolution) and will freeze the video after 6 seconds while audio is continuing when using H264 (as the video file cannot be written properly), as we were saying in this topic.

So, is there a way to tell Chrome not to scale the video but to start directly to record from the requested resolution? Bear in mind that we're already constraining the minimum resolution and Chrome should be respecting this but doesn't!

This is true for H264+Windows 10, so I wonder why the other systems don't respect the constraint. Is this a bug or an expected behavior?

Thanks.

Regards.