The frame recording API tries to only capture compositor frames during which a new content paint made it to the screen. However, the WebRender implementation of frame recording tries to make this distinction by [checking whether any non-root pipelines have updated their epochs](https://searchfox.org/mozilla-central/rev/f4b4008f5ee00f5afa3095f48c54f16828e4b22b/gfx/layers/wr/WebRenderCompositionRecorder.cpp#68-98)... and with WebRender, each video has its own pipeline which updates as the video plays new frames. As a result, pages like cnn.com capture a ton of frames. cnn.com usually has videos below the fold. So we capture a ton of identical browser screenshots, at ~30fps.
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The frame recording API tries to only capture compositor frames during which a new content paint made it to the screen. However, the WebRender implementation of frame recording tries to make this distinction by [checking whether any non-root pipelines have updated their epochs](https://searchfox.org/mozilla-central/rev/c37038c592a352eda0f5e77dfb58c4929bf8bcd3/gfx/webrender_bindings/RendererOGL.cpp#350-381)... and with WebRender, each video has its own pipeline which updates as the video plays new frames. As a result, pages like cnn.com capture a ton of frames. cnn.com usually has videos below the fold. So we capture a ton of identical browser screenshots, at ~30fps.