Reduce buffering for MMAL to avoid requiring 128 MB VRAM split

app/streaming/video/ffmpeg-renderers/mmal.cpp

@@ -22,9 +22,11 @@ MmalRenderer::~MmalRenderer()
     }
 }
 
-bool MmalRenderer::prepareDecoderContext(AVCodecContext*, AVDictionary**)
+bool MmalRenderer::prepareDecoderContext(AVCodecContext*, AVDictionary** options)
 {
-    /* Nothing to do */
+    // FFmpeg defaults this to 10 which is too large to fit in the default 64 MB VRAM split.
+    // Reducing to 2 seems to work fine for our bitstreams (max of 1 buffered frame needed).
+    av_dict_set_int(options, "extra_buffers", 2, 0);
 
     SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                 "Using MMAL renderer");