Support RGB av1 video on native (rerun-io#7726)

### What

Before:
<img width="1104" alt="image"
src="https://github.com/user-attachments/assets/b04cfa05-c52e-4d1d-946f-834dfd4cfaf1">
<img width="1124" alt="image"
src="https://github.com/user-attachments/assets/3fd9889b-ce9d-41b6-bf37-f79222cedbfa">


After:
<img width="1107" alt="image"
src="https://github.com/user-attachments/assets/acdbadbd-cc81-4292-8d20-7b906bdc3c8b">
<img width="1116" alt="image"
src="https://github.com/user-attachments/assets/2000ea97-fb0d-4a77-abaa-a49dbfdc96cc">


### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7726?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7726?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!
* [x] If have noted any breaking changes to the log API in
`CHANGELOG.md` and the migration guide

- [PR Build Summary](https://build.rerun.io/pr/7726)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

To run all checks from `main`, comment on the PR with `@rerun-bot
full-check`.

crates/store/re_video/src/decode/av1.rs

@@ -231,8 +231,7 @@ fn yuv_matrix_coefficients(debug_name: &str, picture: &dav1d::Picture) -> YuvMat
     // Quotes are from https://wiki.x266.mov/docs/colorimetry/matrix (if not noted otherwise)
     #[allow(clippy::match_same_arms)]
     match picture.matrix_coefficients() {
-        // TODO(andreas) This one we should probably support! Afaik this means to just interpret YUV as RGB (or is there a swizzle?).
-        dav1d::pixel::MatrixCoefficients::Identity => YuvMatrixCoefficients::Bt709,
+        dav1d::pixel::MatrixCoefficients::Identity => YuvMatrixCoefficients::Identity,
 
         dav1d::pixel::MatrixCoefficients::BT709 => YuvMatrixCoefficients::Bt709,
 

crates/store/re_video/src/decode/mod.rs

@@ -26,14 +26,13 @@
 //!      * weirdly enough, DO NOT CLAMP! a lot of software may say it's limited but then use the so-called foot and head space anyways to go outside the regular colors
 //!          * reportedly (read this on some forums ;-)) some players _do_ clamp, so let's not get too concerned about this
 //!      * it's a remnant of the analog age, but it's still very common!
-//! * TODO(andreas): It may actually be non-downsampled RGB as well, so skip the entire YUV conversion step! Haven't figured out yet how to determine that.
-//!
 //!
 //! ### Given a normalized YUV triplet, how do we get color?
 //!
 //! * `picture.matrix_coefficients()` (see <https://wiki.x266.mov/docs/colorimetry/matrix>)
 //!   * this tells us what to multiply the incoming YUV data with to get SOME RGB data
 //!   * there's various standards of how to do this, but the most common is BT.709
+//!   * here's a fun special one: `identity` means it's not actually YUV, but GBR!
 //! * `picture.primaries()`
 //!   * now we have RGB but we kinda have no idea what that means!
 //!   * the color primaries tell us which space we're in
@@ -178,6 +177,10 @@ pub enum YuvRange {
 /// For details see `re_renderer`'s `YuvMatrixCoefficients` type.
 #[derive(Debug)]
 pub enum YuvMatrixCoefficients {
+    /// Interpret YUV as GBR.
+    Identity,
+
     Bt601,
+
     Bt709,
 }

crates/viewer/re_renderer/shader/conversions/yuv_converter.wgsl

@@ -25,8 +25,9 @@ const YUV_LAYOUT_YUYV422 = 200u;
 const YUV_LAYOUT_Y400 = 300u;
 
 // see `enum YuvMatrixCoefficients`.
-const COEFFS_BT601 = 0u;
-const COEFFS_BT709 = 1u;
+const COEFFS_IDENTITY = 0u;
+const COEFFS_BT601 = 1u;
+const COEFFS_BT709 = 2u;
 
 // see `enum YuvRange`.
 const YUV_RANGE_LIMITED = 0u;
@@ -73,6 +74,11 @@ fn srgb_from_yuv(yuv: vec3f, yuv_matrix_coefficients: u32, range: u32) -> vec3f
     var rgb: vec3f;
 
     switch (yuv_matrix_coefficients) {
+        case COEFFS_IDENTITY: {
+            // u & v have a range from -0.5 to 0.5. Bring them back to 0-1.
+            rgb = vec3f(v + 0.5, y, u + 0.5);
+        }
+
         // BT.601 (aka. SDTV, aka. Rec.601). wiki: https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
         // Also note according to https://en.wikipedia.org/wiki/SRGB#sYCC_extended-gamut_transformation
         // > Although the RGB color primaries are based on BT.709,

crates/viewer/re_renderer/src/resource_managers/yuv_converter.rs

@@ -187,10 +187,13 @@ pub enum YuvPixelLayout {
 /// …which means for the moment we pretty much only care about the (actually quite) different YUV conversion matrices!
 #[derive(Clone, Copy, Debug)]
 pub enum YuvMatrixCoefficients {
+    /// Identity matrix, interpret YUV as GBR.
+    Identity = 0,
+
     /// BT.601 (aka. SDTV, aka. Rec.601)
     ///
     /// Wiki: <https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion/>
-    Bt601 = 0,
+    Bt601 = 1,
 
     /// BT.709 (aka. HDTV, aka. Rec.709)
     ///
@@ -203,7 +206,7 @@ pub enum YuvMatrixCoefficients {
     /// but for all other purposes they are the same.
     /// (The only reason for us to convert to optical units ("linear" instead of "gamma") is for
     /// lighting & tonemapping where we typically start out with an sRGB image!)
-    Bt709 = 1,
+    Bt709 = 2,
     //
     // Not yet supported. These vary a lot more from the other two!
     //

crates/viewer/re_renderer/src/video/decoder/native_decoder.rs

@@ -178,6 +178,9 @@ fn copy_video_frame_to_texture(
                 re_video::decode::YuvPixelLayout::Y400 => YuvPixelLayout::Y400,
             },
             coefficients: match coefficients {
+                re_video::decode::YuvMatrixCoefficients::Identity => {
+                    YuvMatrixCoefficients::Identity
+                }
                 re_video::decode::YuvMatrixCoefficients::Bt601 => YuvMatrixCoefficients::Bt601,
                 re_video::decode::YuvMatrixCoefficients::Bt709 => YuvMatrixCoefficients::Bt709,
             },