perf(video): 减少闲置缓冲并容忍短时输出背压

src/video/capture/linux.rs

@@ -42,6 +42,12 @@ pub struct CaptureMeta {
     pub sequence: u64,
 }
 
+fn append_capture_plane(dst: &mut Vec<u8>, mapping: &[u8], offset: usize, bytes: usize) {
+    let start = offset.min(mapping.len());
+    let end = offset.saturating_add(bytes).min(mapping.len());
+    dst.extend_from_slice(&mapping[start..end]);
+}
+
 /// When set, DV ioctls use the subdev (rkcif: video node has no DV ioctls).
 #[derive(Debug, Clone, Default)]
 pub struct BridgeContext {
@@ -629,12 +635,12 @@ impl CaptureStream {
             }
             let mapping = &self.mappings[index][plane_idx];
             let start = data_offset.min(mapping.len());
-            let end = (data_offset + bytes_used).min(mapping.len());
+            let end = data_offset.saturating_add(bytes_used).min(mapping.len());
             total += end.saturating_sub(start);
         }
 
-        dst.resize(total, 0);
-        let mut cursor = 0usize;
+        dst.clear();
+        dst.reserve(total);
         for (plane_idx, plane) in dqbuf.planes_iter().enumerate() {
             let bytes_used = *plane.bytesused as usize;
             let data_offset = plane.data_offset.copied().unwrap_or(0) as usize;
@@ -642,14 +648,7 @@ impl CaptureStream {
                 continue;
             }
             let mapping = &self.mappings[index][plane_idx];
-            let start = data_offset.min(mapping.len());
-            let end = (data_offset + bytes_used).min(mapping.len());
-            let len = end.saturating_sub(start);
-            if len == 0 {
-                continue;
-            }
-            dst[cursor..cursor + len].copy_from_slice(&mapping[start..end]);
-            cursor += len;
+            append_capture_plane(dst, mapping, data_offset, bytes_used);
         }
 
         self.queue_buffer(index as u32)
@@ -1153,9 +1152,23 @@ fn set_fps(fd: &File, queue: QueueType, fps: u32) -> std::result::Result<(), ioc
 
 #[cfg(test)]
 mod tests {
-    use super::{open_capture_device, DvTimingsSignature, NativeHdmirxState};
+    use super::{append_capture_plane, open_capture_device, DvTimingsSignature, NativeHdmirxState};
     use crate::video::format::PixelFormat;
 
+    #[test]
+    fn capture_planes_append_without_stale_bytes_or_reallocation() {
+        let mut data = vec![99; 64];
+        let pointer = data.as_ptr();
+        data.clear();
+        append_capture_plane(&mut data, &[1, 2, 3, 4], 1, 2);
+        append_capture_plane(&mut data, &[5, 6, 7], 0, 10);
+        assert_eq!(data, [2, 3, 5, 6, 7]);
+        assert_eq!(data.as_ptr(), pointer);
+        append_capture_plane(&mut data, &[8], usize::MAX, usize::MAX);
+        append_capture_plane(&mut data, &[8], 0, 0);
+        assert_eq!(data, [2, 3, 5, 6, 7]);
+    }
+
     fn timing() -> DvTimingsSignature {
         DvTimingsSignature {
             width: 1920,

src/video/codec/convert.rs

@@ -544,7 +544,7 @@ pub struct Nv12Converter {
 /// MJPEG decoder that writes NV12 directly using libyuv.
 pub struct MjpegToNv12Decoder {
     resolution: Resolution,
-    output_buffer: Nv12Buffer,
+    output_buffer: Option<Nv12Buffer>,
     size_checked: bool,
 }
 
@@ -552,7 +552,7 @@ impl MjpegToNv12Decoder {
     pub fn new(resolution: Resolution) -> Self {
         Self {
             resolution,
-            output_buffer: Nv12Buffer::new(resolution),
+            output_buffer: None,
             size_checked: false,
         }
     }
@@ -561,11 +561,14 @@ impl MjpegToNv12Decoder {
         self.check_size(input)?;
         let width = self.resolution.width as i32;
         let height = self.resolution.height as i32;
+        let output = self
+            .output_buffer
+            .get_or_insert_with(|| Nv12Buffer::new(self.resolution));
 
-        libyuv::mjpg_to_nv12(input, self.output_buffer.as_bytes_mut(), width, height)
+        libyuv::mjpg_to_nv12(input, output.as_bytes_mut(), width, height)
             .map_err(|e| AppError::VideoError(format!("libyuv MJPEG->NV12 failed: {}", e)))?;
 
-        Ok(self.output_buffer.as_bytes())
+        Ok(output.as_bytes())
     }
 
     /// Decode into caller-owned storage so capture and encoding can run on
@@ -899,6 +902,7 @@ mod tests {
         let mut output = Vec::with_capacity(output_size);
         let allocation = output.as_ptr();
         let mut decoder = MjpegToNv12Decoder::new(resolution);
+        assert!(decoder.output_buffer.is_none());
 
         decoder.decode_into(&jpeg, &mut output).unwrap();
         assert_eq!(output.len(), output_size);
@@ -907,5 +911,10 @@ mod tests {
         decoder.decode_into(&jpeg, &mut output).unwrap();
         assert_eq!(output.len(), output_size);
         assert_eq!(output.as_ptr(), allocation);
+
+        assert!(decoder.output_buffer.is_none());
+        assert_eq!(decoder.decode(&jpeg).unwrap(), output.as_slice());
+        let internal = decoder.decode(&jpeg).unwrap().as_ptr();
+        assert_eq!(decoder.decode(&jpeg).unwrap().as_ptr(), internal);
     }
 }

src/video/pipeline/shared.rs

@@ -157,6 +157,11 @@ use crate::video::recovery::{wait_for_source_change, CaptureRecoveryPolicy};
 use crate::video::signal::SignalStatus;
 
 const MIN_CAPTURE_FRAME_SIZE: usize = 128;
+const OUTPUT_BACKPRESSURE_GRACE_NS: u64 = 10_000_000;
+
+fn sustained_output_backpressure(started_ns: u64, now_ns: u64) -> bool {
+    started_ns != 0 && now_ns.saturating_sub(started_ns - 1) >= OUTPUT_BACKPRESSURE_GRACE_NS
+}
 type VideoFrameMailbox = FrameMailbox<Arc<VideoFrame>>;
 
 fn spawn_video_worker(
@@ -637,6 +642,7 @@ pub struct SharedVideoPipeline {
     encoder_output_wait_ns: AtomicU64,
     output_backpressure_events: AtomicU64,
     output_backpressured: AtomicBool,
+    output_backpressure_since_ns: AtomicU64,
     encoded_frames_skipped_for_slow_subscribers: AtomicU64,
     delivery_stats: Arc<DeliveryStats>,
     running: watch::Sender<bool>,
@@ -704,6 +710,7 @@ impl SharedVideoPipeline {
             encoder_output_wait_ns: AtomicU64::new(0),
             output_backpressure_events: AtomicU64::new(0),
             output_backpressured: AtomicBool::new(false),
+            output_backpressure_since_ns: AtomicU64::new(0),
             encoded_frames_skipped_for_slow_subscribers: AtomicU64::new(0),
             delivery_stats: Arc::new(DeliveryStats::default()),
             running: running_tx,
@@ -911,6 +918,13 @@ impl SharedVideoPipeline {
         stage: MjpegAdmissionStage,
     ) -> bool {
         let backpressured = self.output_backpressured.load(Ordering::Acquire);
+        if backpressured && policy == MjpegAdmissionPolicy::BoundedPrefetch {
+            let started = self.output_backpressure_since_ns.load(Ordering::Acquire);
+            let now = PROCESS_START.get_or_init(Instant::now).elapsed().as_nanos() as u64;
+            if !sustained_output_backpressure(started, now) {
+                return false;
+            }
+        }
         if !policy.check_pending(backpressured) {
             return false;
         }
@@ -1081,6 +1095,11 @@ impl SharedVideoPipeline {
             }
         }
         if active_subscribers > 0 && reservations.is_empty() {
+            if !self.output_backpressured.load(Ordering::Acquire) {
+                let now = PROCESS_START.get_or_init(Instant::now).elapsed().as_nanos() as u64;
+                self.output_backpressure_since_ns
+                    .store(now.saturating_add(1), Ordering::Release);
+            }
             if !self.output_backpressured.swap(true, Ordering::AcqRel) {
                 self.output_backpressure_events
                     .fetch_add(1, Ordering::Relaxed);
@@ -1088,6 +1107,8 @@ impl SharedVideoPipeline {
             None
         } else {
             self.output_backpressured.store(false, Ordering::Release);
+            self.output_backpressure_since_ns
+                .store(0, Ordering::Release);
             Some(reservations)
         }
     }
@@ -1302,6 +1323,8 @@ impl SharedVideoPipeline {
         self.encoder_output_wait_ns.store(0, Ordering::Relaxed);
         self.output_backpressure_events.store(0, Ordering::Relaxed);
         self.output_backpressured.store(false, Ordering::Release);
+        self.output_backpressure_since_ns
+            .store(0, Ordering::Release);
         self.encoded_frames_skipped_for_slow_subscribers
             .store(0, Ordering::Relaxed);
         self.delivery_stats.sent_frames.store(0, Ordering::Relaxed);
@@ -2538,6 +2561,15 @@ mod tests {
         assert_eq!(stats.decoded_frames_not_encoded, 5);
     }
 
+    #[test]
+    fn brief_output_backpressure_keeps_bounded_prefetch_running() {
+        assert!(!sustained_output_backpressure(0, 100_000_000));
+        assert!(!sustained_output_backpressure(1, 9_999_999));
+        assert!(sustained_output_backpressure(1, 10_000_000));
+        assert!(sustained_output_backpressure(1, 100_000_000));
+        assert!(!sustained_output_backpressure(20_000_001, 10_000_000));
+    }
+
     #[test]
     fn mjpeg_drop_reasons_sum_to_total_without_double_counting() {
         let pipeline = delivery_test_pipeline();
@@ -2606,6 +2638,7 @@ mod tests {
         }
         mailbox.publish(1, delivery_test_raw_frame(1));
         for stage in [MjpegAdmissionStage::Capture, MjpegAdmissionStage::Decode] {
+            std::thread::sleep(Duration::from_millis(11));
             assert!(pipeline.drop_pending_mjpeg(
                 &mailbox,
                 MjpegAdmissionPolicy::BoundedPrefetch,