feat: 支持 MJPEG 解码与 MSD 目录配置

- FFmpeg/hwcodec 增加 RKMPP MJPEG 解码与 RAM FFI，ARM 构建启用对应解码器
  - 共享视频管线新增 MJPEG 解码路径（RKMPP/TurboJPEG），优化 WebRTC 发送与 MJPEG 去重
  - MSD 配置改为 msd_dir 并自动创建子目录，接口与前端设置同步更新
  - 更新包依赖与版本号

src/video/decoder/mjpeg_rkmpp.rs

@@ -0,0 +1,95 @@
+//! MJPEG decoder using RKMPP via hwcodec (FFmpeg RAM).
+
+use hwcodec::ffmpeg::AVPixelFormat;
+use hwcodec::ffmpeg_ram::decode::{DecodeContext, Decoder};
+use tracing::warn;
+
+use crate::error::{AppError, Result};
+use crate::video::convert::Nv12Converter;
+use crate::video::format::Resolution;
+
+pub struct MjpegRkmppDecoder {
+    decoder: Decoder,
+    resolution: Resolution,
+    nv16_to_nv12: Option<Nv12Converter>,
+    last_pixfmt: Option<AVPixelFormat>,
+}
+
+impl MjpegRkmppDecoder {
+    pub fn new(resolution: Resolution) -> Result<Self> {
+        let ctx = DecodeContext {
+            name: "mjpeg_rkmpp".to_string(),
+            width: resolution.width as i32,
+            height: resolution.height as i32,
+            sw_pixfmt: AVPixelFormat::AV_PIX_FMT_NV12,
+            thread_count: 1,
+        };
+        let decoder = Decoder::new(ctx).map_err(|_| {
+            AppError::VideoError("Failed to create mjpeg_rkmpp decoder".to_string())
+        })?;
+        Ok(Self {
+            decoder,
+            resolution,
+            nv16_to_nv12: None,
+            last_pixfmt: None,
+        })
+    }
+
+    pub fn decode_to_nv12(&mut self, mjpeg: &[u8]) -> Result<Vec<u8>> {
+        let frames = self
+            .decoder
+            .decode(mjpeg)
+            .map_err(|e| AppError::VideoError(format!("mjpeg_rkmpp decode failed: {}", e)))?;
+        if frames.is_empty() {
+            return Err(AppError::VideoError(
+                "mjpeg_rkmpp decode returned no frames".to_string(),
+            ));
+        }
+        if frames.len() > 1 {
+            warn!(
+                "mjpeg_rkmpp decode returned {} frames, using last",
+                frames.len()
+            );
+        }
+        let frame = frames
+            .pop()
+            .ok_or_else(|| AppError::VideoError("mjpeg_rkmpp decode returned empty".to_string()))?;
+
+        if frame.width as u32 != self.resolution.width
+            || frame.height as u32 != self.resolution.height
+        {
+            warn!(
+                "mjpeg_rkmpp output size {}x{} differs from expected {}x{}",
+                frame.width, frame.height, self.resolution.width, self.resolution.height
+            );
+        }
+
+        if let Some(last) = self.last_pixfmt {
+            if frame.pixfmt != last {
+                warn!(
+                    "mjpeg_rkmpp output pixfmt changed from {:?} to {:?}",
+                    last, frame.pixfmt
+                );
+            }
+        } else {
+            self.last_pixfmt = Some(frame.pixfmt);
+        }
+
+        let pixfmt = self.last_pixfmt.unwrap_or(frame.pixfmt);
+        match pixfmt {
+            AVPixelFormat::AV_PIX_FMT_NV12 => Ok(frame.data),
+            AVPixelFormat::AV_PIX_FMT_NV16 => {
+                if self.nv16_to_nv12.is_none() {
+                    self.nv16_to_nv12 = Some(Nv12Converter::nv16_to_nv12(self.resolution));
+                }
+                let conv = self.nv16_to_nv12.as_mut().unwrap();
+                let nv12 = conv.convert(&frame.data)?;
+                Ok(nv12.to_vec())
+            }
+            other => Err(AppError::VideoError(format!(
+                "mjpeg_rkmpp output pixfmt {:?} (expected NV12/NV16)",
+                other
+            ))),
+        }
+    }
+}

src/video/decoder/mjpeg_turbo.rs

@@ -0,0 +1,54 @@
+//! MJPEG decoder using TurboJPEG (software) -> RGB24.
+
+use turbojpeg::{Decompressor, Image, PixelFormat as TJPixelFormat};
+
+use crate::error::{AppError, Result};
+use crate::video::format::Resolution;
+
+pub struct MjpegTurboDecoder {
+    decompressor: Decompressor,
+    resolution: Resolution,
+}
+
+impl MjpegTurboDecoder {
+    pub fn new(resolution: Resolution) -> Result<Self> {
+        let decompressor = Decompressor::new().map_err(|e| {
+            AppError::VideoError(format!("Failed to create turbojpeg decoder: {}", e))
+        })?;
+        Ok(Self {
+            decompressor,
+            resolution,
+        })
+    }
+
+    pub fn decode_to_rgb(&mut self, mjpeg: &[u8]) -> Result<Vec<u8>> {
+        let header = self
+            .decompressor
+            .read_header(mjpeg)
+            .map_err(|e| AppError::VideoError(format!("turbojpeg read_header failed: {}", e)))?;
+
+        if header.width as u32 != self.resolution.width
+            || header.height as u32 != self.resolution.height
+        {
+            return Err(AppError::VideoError(format!(
+                "turbojpeg size mismatch: {}x{} (expected {}x{})",
+                header.width, header.height, self.resolution.width, self.resolution.height
+            )));
+        }
+
+        let pitch = header.width * 3;
+        let mut image = Image {
+            pixels: vec![0u8; header.height * pitch],
+            width: header.width,
+            pitch,
+            height: header.height,
+            format: TJPixelFormat::RGB,
+        };
+
+        self.decompressor
+            .decompress(mjpeg, image.as_deref_mut())
+            .map_err(|e| AppError::VideoError(format!("turbojpeg decode failed: {}", e)))?;
+
+        Ok(image.pixels)
+    }
+}

src/video/decoder/mod.rs

@@ -1,3 +1,11 @@
 //! Video decoder implementations
 //!
 //! This module provides video decoding capabilities.
+
+#[cfg(any(target_arch = "aarch64", target_arch = "arm"))]
+pub mod mjpeg_rkmpp;
+pub mod mjpeg_turbo;
+
+#[cfg(any(target_arch = "aarch64", target_arch = "arm"))]
+pub use mjpeg_rkmpp::MjpegRkmppDecoder;
+pub use mjpeg_turbo::MjpegTurboDecoder;