Try main.cpp instead of c.

Makefile

@@ -1,8 +1,21 @@
+# dist/ffmpeg-webtools.js:
+# 	mkdir -p dist && \
+# 	emcc -L/opt/ffmpeg/lib -I/opt/ffmpeg/include/ src/main.c \
+# 	-s EXPORTED_FUNCTIONS='["_c_avformat_version", "_openfile", "_addOne"]' \
+# 	-s EXTRA_EXPORTED_RUNTIME_METHODS="[FS, cwrap, ccall, getValue, setValue, writeAsciiToMemory]" \
+# 	-s INITIAL_MEMORY=268435456 \
+# 	-lavcodec -lavformat -lavfilter -lavdevice -lswresample -lswscale -lavutil -lm -lx264 -pthread \
+# 	-o www/public/ffmpeg-webtools.js
+
 dist/ffmpeg-webtools.js:
 	mkdir -p dist && \
-	emcc -L/opt/ffmpeg/lib -I/opt/ffmpeg/include/ src/main.c \
+	emcc  \
-	-s EXPORTED_FUNCTIONS='["_version", "_openfile"]' \
+	--bind \
-	-s EXTRA_EXPORTED_RUNTIME_METHODS="[FS, cwrap, ccall, setValue, writeAsciiToMemory]" \
+	-L/opt/ffmpeg/lib \
+	-I/opt/ffmpeg/include/ \
+ 	-s EXTRA_EXPORTED_RUNTIME_METHODS="[FS, cwrap, ccall, getValue, setValue, writeAsciiToMemory]" \
  	-s INITIAL_MEMORY=268435456 \
+	-pthread \
  	-lavcodec -lavformat -lavfilter -lavdevice -lswresample -lswscale -lavutil -lm -lx264 -pthread \
-	-o $@
+	-o www/public/ffmpeg-webtools.js \
+	src/main.cpp

src/main.cpp

@@ -0,0 +1,72 @@
+#include <emscripten.h>
+#include <emscripten/bind.h>
+
+
+using namespace emscripten;
+
+
+extern "C" {
+
+#include <libavcodec/avcodec.h>
+#include <libavformat/avformat.h>
+#include <libavutil/avutil.h>
+
+
+const std::string c_avformat_version() {
+    return AV_STRINGIFY(LIBAVFORMAT_VERSION);
+}
+
+struct Response {
+  std::string name;
+  int bit_rate;
+  int duration;
+};
+
+Response c_openfile() {
+    FILE *file = fopen("testingfs", "rb");
+    if (!file) {
+      printf("cannot open file\n");
+    }
+    fclose(file);
+
+    AVFormatContext *pFormatContext = avformat_alloc_context();
+    if (!pFormatContext) {
+      printf("ERROR: could not allocate memory for Format Context\n");
+    }
+    printf("%p\n", pFormatContext);
+
+    printf("opening the input file: %s and loading format (container) header\n", "testingfs");
+
+    // Open the file and read header.
+    int ret;
+    if ((ret = avformat_open_input(&pFormatContext, "testingfs", NULL, NULL)) < 0) {
+        printf("ERROR: could not open the file. Error: %d\n", ret);
+        printf("%s", av_err2str(ret));
+    }
+
+    printf("format: %s, duration: %lld us, bit_rate: %lld\n",
+      pFormatContext->iformat->name,
+      pFormatContext->duration,
+      pFormatContext->bit_rate);
+
+    Response r;
+    r.name = pFormatContext->iformat->name;
+    r.duration = pFormatContext->duration;
+    r.bit_rate = pFormatContext->bit_rate;
+    return r;
+}
+};
+
+
+EMSCRIPTEN_BINDINGS(my_constant_example) {
+    function("c_avformat_version", &c_avformat_version);
+}
+
+EMSCRIPTEN_BINDINGS(a_struct) {
+  emscripten::value_object<Response>("Response")
+  .field("name", &Response::name)
+  .field("duration", &Response::duration)
+  .field("bit_rate", &Response::bit_rate)
+  ;
+  function("c_openfile", &c_openfile);
+}

www/src/components/File.vue

@@ -22,7 +22,10 @@
           <div class="mt-3">Selected file: {{ file ? `${file.name}: ${file.size} bytes` : '' }}</div>
           <hr />
           {{ info }}
+
+          avformat_version: {{ avformat_version }}
         </div>
+
     </div>
 </template>
 
@@ -40,14 +43,17 @@ export default {
     }
   },
   computed: {
+    avformat_version() {
+      // return window.Module.ccall('c_avformat_version', 'string');
+      return window.Module.c_avformat_version();
+    },
     info() {
-
       const data = this.data;
       console.log('writing data to memfs');
       window.Module.FS.writeFile('testingfs', new Uint8Array(data));
       console.log('writing data to memfs done');
 
-      window.Module.ccall('version');
+      // window.Module.ccall('version');
       // Window.Module.ccall('openfile');
       return 'info';
     }