Make VideoDecoder a trait (#7577)

### What
* Part of #7298 

### Checklist
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* Using examples from latest `main` build:
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* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7577?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
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crates/viewer/re_renderer/src/video/decoder/mod.rs

@@ -1,17 +1,52 @@
 #[cfg(target_arch = "wasm32")]
 mod web;
-#[cfg(target_arch = "wasm32")]
-pub use web::VideoDecoder;
 
-// TODO(#7298): decode on native
 #[cfg(not(target_arch = "wasm32"))]
 mod native;
-#[cfg(not(target_arch = "wasm32"))]
-pub use native::VideoDecoder;
+use crate::{
+    resource_managers::GpuTexture2D,
+    wgpu_resources::{GpuTexturePool, TextureDesc},
+    RenderContext,
+};
+
+use std::sync::Arc;
+
+use super::{DecodeHardwareAcceleration, DecodingError, FrameDecodingResult};
+
+/// Decode video to a texture.
+///
+/// If you want to sample multiple points in a video simultaneously, use multiple decoders.
+pub trait VideoDecoder: 'static + Send {
+    /// Get the video frame at the given time stamp.
+    ///
+    /// This will seek in the video if needed.
+    /// If you want to sample multiple points in a video simultaneously, use multiple decoders.
+    fn frame_at(
+        &mut self,
+        render_ctx: &RenderContext,
+        presentation_timestamp_s: f64,
+    ) -> FrameDecodingResult;
+}
 
-use crate::resource_managers::GpuTexture2D;
-use crate::wgpu_resources::GpuTexturePool;
-use crate::wgpu_resources::TextureDesc;
+#[cfg(target_arch = "wasm32")]
+pub fn new_video_decoder(
+    render_context: &RenderContext,
+    data: Arc<re_video::VideoData>,
+    hw_acceleration: DecodeHardwareAcceleration,
+) -> Result<Box<dyn VideoDecoder>, DecodingError> {
+    let decoder = web::WebVideoDecoder::new(render_context, data, hw_acceleration)?;
+    Ok(Box::new(decoder))
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn new_video_decoder(
+    render_context: &RenderContext,
+    data: Arc<re_video::VideoData>,
+    _hw_acceleration: DecodeHardwareAcceleration,
+) -> Result<Box<dyn VideoDecoder>, DecodingError> {
+    let decoder = native::NoNativeVideoDecoder::new(render_context, data)?;
+    Ok(Box::new(decoder))
+}
 
 fn alloc_video_frame_texture(
     device: &wgpu::Device,

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

@@ -1,29 +1,31 @@
+// TODO(#7298): decode on native
+
 #![allow(dead_code, unused_variables, clippy::unnecessary_wraps)]
 
 use std::sync::Arc;
 
 use crate::{
     resource_managers::GpuTexture2D,
-    video::{DecodeHardwareAcceleration, DecodingError, FrameDecodingResult},
+    video::{DecodingError, FrameDecodingResult},
     RenderContext,
 };
 
 // TODO(#7298): remove `allow` once we have native video decoding
 #[allow(unused_imports)]
 use super::latest_at_idx;
 
-use super::alloc_video_frame_texture;
+use super::{alloc_video_frame_texture, VideoDecoder};
 
-pub struct VideoDecoder {
+/// A [`VideoDecoder`] that always fails.
+pub struct NoNativeVideoDecoder {
     data: Arc<re_video::VideoData>,
     zeroed_texture: GpuTexture2D,
 }
 
-impl VideoDecoder {
+impl NoNativeVideoDecoder {
     pub fn new(
         render_context: &RenderContext,
         data: Arc<re_video::VideoData>,
-        _hw_acceleration: DecodeHardwareAcceleration,
     ) -> Result<Self, DecodingError> {
         let device = render_context.device.clone();
         let zeroed_texture = alloc_video_frame_texture(
@@ -37,9 +39,11 @@ impl VideoDecoder {
             zeroed_texture,
         })
     }
+}
 
+impl VideoDecoder for NoNativeVideoDecoder {
     #[allow(clippy::unused_self)]
-    pub fn frame_at(
+    fn frame_at(
         &mut self,
         _render_ctx: &RenderContext,
         _presentation_timestamp_s: f64,

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

@@ -10,13 +10,14 @@ use web_sys::{
 };
 use web_time::Instant;
 
-use super::latest_at_idx;
 use crate::{
     resource_managers::GpuTexture2D,
     video::{DecodeHardwareAcceleration, DecodingError, FrameDecodingResult, VideoFrameTexture},
     DebugLabel, RenderContext,
 };
 
+use super::{latest_at_idx, VideoDecoder};
+
 #[derive(Clone)]
 #[repr(transparent)]
 struct VideoFrame(web_sys::VideoFrame);
@@ -61,7 +62,7 @@ struct DecoderOutput {
 /// transient errors without flickering.
 const DECODING_ERROR_REPORTING_DELAY: Duration = Duration::from_millis(400);
 
-pub struct VideoDecoder {
+pub struct WebVideoDecoder {
     data: Arc<re_video::VideoData>,
     queue: Arc<wgpu::Queue>,
     texture: GpuTexture2D,
@@ -83,11 +84,11 @@ pub struct VideoDecoder {
 #[allow(unsafe_code)]
 // Clippy did not recognize a safety comment on these impls no matter what I tried:
 #[allow(clippy::undocumented_unsafe_blocks)]
-unsafe impl Send for VideoDecoder {}
+unsafe impl Send for WebVideoDecoder {}
 
 #[allow(unsafe_code)]
 #[allow(clippy::undocumented_unsafe_blocks)]
-unsafe impl Sync for VideoDecoder {}
+unsafe impl Sync for WebVideoDecoder {}
 
 #[allow(unsafe_code)]
 #[allow(clippy::undocumented_unsafe_blocks)]
@@ -97,9 +98,9 @@ unsafe impl Send for VideoFrame {}
 #[allow(clippy::undocumented_unsafe_blocks)]
 unsafe impl Sync for VideoFrame {}
 
-impl Drop for VideoDecoder {
+impl Drop for WebVideoDecoder {
     fn drop(&mut self) {
-        re_log::debug!("Dropping VideoDecoder");
+        re_log::debug!("Dropping WebVideoDecoder");
         if let Err(err) = self.decoder.close() {
             if let Some(dom_exception) = err.dyn_ref::<web_sys::DomException>() {
                 if dom_exception.code() == web_sys::DomException::INVALID_STATE_ERR
@@ -118,7 +119,7 @@ impl Drop for VideoDecoder {
     }
 }
 
-impl VideoDecoder {
+impl WebVideoDecoder {
     pub fn new(
         render_context: &RenderContext,
         data: Arc<re_video::VideoData>,
@@ -157,8 +158,10 @@ impl VideoDecoder {
             error_on_last_frame_at: false,
         })
     }
+}
 
-    pub fn frame_at(
+impl VideoDecoder for WebVideoDecoder {
+    fn frame_at(
         &mut self,
         render_ctx: &RenderContext,
         presentation_timestamp_s: f64,
@@ -185,7 +188,9 @@ impl VideoDecoder {
         }
         result
     }
+}
 
+impl WebVideoDecoder {
     fn frame_at_internal(&mut self, presentation_timestamp_s: f64) -> FrameDecodingResult {
         if presentation_timestamp_s < 0.0 {
             return Err(DecodingError::NegativeTimestamp);

crates/viewer/re_renderer/src/video/mod.rs

@@ -67,7 +67,7 @@ pub enum VideoFrameTexture {
 pub struct VideoDecodingStreamId(pub u64);
 
 struct DecoderEntry {
-    decoder: decoder::VideoDecoder,
+    decoder: Box<dyn decoder::VideoDecoder>,
     frame_index: u64,
 }
 
@@ -192,7 +192,7 @@ impl Video {
         let decoder_entry = match decoders.entry(decoder_stream_id) {
             Entry::Occupied(occupied_entry) => occupied_entry.into_mut(),
             Entry::Vacant(vacant_entry) => {
-                let new_decoder = decoder::VideoDecoder::new(
+                let new_decoder = decoder::new_video_decoder(
                     render_context,
                     self.data.clone(),
                     self.decode_hw_acceleration,