Build FFmpeg with v4l2 support for Linux

So that --v4l2-sink works with Linux static builds.

.github/workflows/release.yml

@@ -77,7 +77,8 @@ jobs:
           sudo apt update
           sudo apt install -y meson ninja-build nasm ffmpeg libsdl2-2.0-0 \
              libsdl2-dev libavcodec-dev libavdevice-dev libavformat-dev \
-             libavutil-dev libswresample-dev libusb-1.0-0 libusb-1.0-0-dev
+             libavutil-dev libswresample-dev libusb-1.0-0 libusb-1.0-0-dev \
+             libv4l-dev
 
       - name: Test
         run: release/test_client.sh
@@ -93,7 +94,8 @@ jobs:
           sudo apt update
           sudo apt install -y meson ninja-build nasm ffmpeg libsdl2-2.0-0 \
              libsdl2-dev libavcodec-dev libavdevice-dev libavformat-dev \
-             libavutil-dev libswresample-dev libusb-1.0-0 libusb-1.0-0-dev
+             libavutil-dev libswresample-dev libusb-1.0-0 libusb-1.0-0-dev \
+             libv4l-dev
 
       - name: Build linux
         run: release/build_linux.sh

app/deps/ffmpeg.sh

@@ -81,8 +81,14 @@ else
         --enable-muxer=wav
     )
 
-    if [[ "$HOST" != linux ]]
+    if [[ "$HOST" == linux ]]
     then
+        conf+=(
+            --enable-libv4l2
+            --enable-outdev=v4l2
+            --enable-encoder=rawvideo
+        )
+    else
         # libavdevice is only used for V4L2 on Linux
         conf+=(
             --disable-avdevice