Improving encoding quality of Hantro H1 encoder (NXP i.MX8M Mini)

[jpeeee]

Hello,

I'm using an i.MX8MMini to encode live video + overlays to H.264. I am trying to improve the video quality for a given bitrate.
The SoC uses the Hantro H1 encoder.

It defaults to Baseline profile and I've enabled CABAC and 8x8 transform in the vpu wrapper library, thus setting it to High profile. Those two are the only features that are more or less clearly documented. I've been able to verify that the changes were taken into account by the encoder using StreamEye and can see a modest improvement on the video quality. However, it's still not as good as other video encoders I'm comparing with. I'm testing encoding at 5Mbps, with auto Qp and Gop=15.

I was wondering if anyone on this forum had any experience with the Hantro H1 encoder? If so, do you have any qualitative comparison with other encoders?

The poor quality of the encoded video is particularly visible around the text overlay when the text is set on transparent background. I am using a non-smooth font so the pixels are either opaque or transparent, and there is no alpha-blending taking place, so the text is expected to be jagged. I have tried alpha-blending a smooth font, with similar outcome.

I attach a 2 sec recording made with the encoder - gop=15, bitrate=5000, qp=-1 (auto). There are strong artefacts around the text. At the same bitrate, they do not appear with a competitor's encoder.

I apologise if my post is a bit wooly; I'm on a learning curve when it comes to video encoding / H.264.

I should add that I don't have access to the datasheet for the Hantro H1; just a list of sparsly documented registers.

Thanks