Fix Linux CI builds by downgrading rsmpeg for FFmpeg 6.x compatibility

Add steps to Linux CI workflows to temporarily downgrade rsmpeg from
0.18.0 (FFmpeg 8.0) to 0.14.2 (FFmpeg 6.1) since Ubuntu runners have
older FFmpeg versions installed.

This allows the CI to build successfully while keeping FFmpeg 8.0
support for users who have it installed locally.

Author: prateekmedia

.github/workflows/build_linux.yml

@@ -28,6 +28,9 @@ jobs:
     - name: Install dependencies
       run: sudo apt update && sudo apt-get install libgpac-dev libtesseract-dev libavcodec-dev libavdevice-dev libx11-dev libxcb1-dev libxcb-shm0-dev
     - uses: actions/checkout@v4
+    - name: Downgrade rsmpeg for FFmpeg 6.x compatibility
+      run: |
+        sed -i 's/rsmpeg = { version = "0.18.0+ffmpeg.8.0"/rsmpeg = { version = "0.14.2+ffmpeg.6.1"/' src/rust/Cargo.toml
     - name: build
       run: ./build -hardsubx
       working-directory: ./linux
@@ -79,6 +82,9 @@ jobs:
     - uses: actions/checkout@v4
     - name: Install dependencies
       run: sudo apt update && sudo apt install libgpac-dev libtesseract-dev libavformat-dev libavdevice-dev libswscale-dev yasm
+    - name: Downgrade rsmpeg for FFmpeg 6.x compatibility
+      run: |
+        sed -i 's/rsmpeg = { version = "0.18.0+ffmpeg.8.0"/rsmpeg = { version = "0.14.2+ffmpeg.6.1"/' src/rust/Cargo.toml
     - name: cmake
       run: |
         mkdir build && cd build