ci: add explicit build test for ffmpeg 4.4

This uses an alpine 3.15 container, which should be one of the oldest
distros that mpv master can compile on and that uses ffmpeg 4.4. Some
functionality is missing due to library versions being too old on
alpine, e.g. wayland, mujs, and pipewire.

The alpine build is also explicitly minimal, to test builds in
conditions where many common mpv features may not be available.

.github/workflows/build.yml

@@ -205,6 +205,58 @@ jobs:
         run: |
           cat ./build/meson-logs/testlog.txt
 
+  linux-ffmpeg-4-4:
+    runs-on: ubuntu-22.04
+    container:
+      # We want to test ffmpeg 4.4 which alpine 3.15 has exactly.
+      # Furthermore, this is a very minimal build of mpv without commonly
+      # used features to test build compatibility. Musl is a nice bonus as well
+      image: alpine:3.15
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: |
+          apk update
+          apk add \
+              binutils \
+              ffmpeg-dev \
+              gcc \
+              git \
+              g++ \
+              libass-dev \
+              lua5.2-dev \
+              pulseaudio-dev \
+              libx11-dev \
+              libxfixes-dev \
+              libxkbcommon-dev \
+              libxrandr-dev \
+              libxpresent-dev \
+              libxscrnsaver-dev \
+              musl-dev \
+              py3-pip \
+              samurai
+              pip install meson
+
+      - name: Build with meson
+        id: build
+        run: |
+              ./ci/build-linux-old.sh
+
+      - name: Print meson log
+        if: ${{ failure() && steps.build.outcome == 'failure' }}
+        run: |
+          cat ./build/meson-logs/meson-log.txt
+
+      - name: Run meson tests
+        id: tests
+        run: |
+          meson test -C build
+
+      - name: Print meson test log
+        if: ${{ failure() && steps.tests.outcome == 'failure' }}
+        run: |
+          cat ./build/meson-logs/testlog.txt
+
   openbsd:
     runs-on: ubuntu-latest # until https://github.com/actions/runner/issues/385
     timeout-minutes: 30 # avoid any weirdness with the VM

ci/build-linux-old.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+
+# clone exactly the oldest libplacebo we want to support
+rm -rf subprojects
+mkdir -p subprojects
+git clone https://code.videolan.org/videolan/libplacebo.git \
+    --depth 1 --branch v6.338 --recurse-submodules subprojects/libplacebo
+
+meson setup build \
+    -Dlibplacebo:vulkan=disabled \
+    -Dlibmpv=true \
+    -Dlua=enabled \
+    -Dtests=true
+
+meson compile -C build
+./build/mpv -v --no-config