ios support (ffmpegwasm#15)

* Revert "Upgrade to emscripten v2.0.24"
Because of confusing due to API changes.

* ios support

Co-authored-by: jeromewu <jeromewus@gmail.com>

Author: novogrammer

wasm/build-scripts/build-ffmpeg.sh

@@ -30,10 +30,11 @@ FLAGS=(
   -s EXIT_RUNTIME=1                             # exit runtime after execution
   -s MODULARIZE=1                               # use modularized version to be more flexible
   -s EXPORT_NAME="createFFmpegCore"             # assign export name for browser
-
   -s EXPORTED_FUNCTIONS="$EXPORTED_FUNCTIONS"  # export main and proxy_main funcs
-  -s EXPORTED_RUNTIME_METHODS="[FS, cwrap, ccall, setValue, writeAsciiToMemory, lengthBytesUTF8, stringToUTF8, UTF8ToString]"   # export preamble funcs
-  -s INITIAL_MEMORY=2146435072                  # 64 KB * 1024 * 16 * 2047 = 2146435072 bytes ~= 2 GB
+  -s EXTRA_EXPORTED_RUNTIME_METHODS="[FS, cwrap, ccall, setValue, writeAsciiToMemory, lengthBytesUTF8, stringToUTF8, UTF8ToString]"   # export preamble funcs
+  -s INITIAL_MEMORY=33554432                    # 32MB
+  -s MAXIMUM_MEMORY=1073741824                  # 1GB
+  -s ALLOW_MEMORY_GROWTH=1
   --post-js wasm/src/post.js
   --pre-js wasm/src/pre.js
   $OPTIM_FLAGS