Improved stability for mp4 parser when dealing with corrupted FTYP bo…

…xes (#241)

* Fixing issues when inconsistent size information on ftyp boxes caused MP4 parser to throw errors instead of rejecting the files

lib/parsers/mp4_parser.rb

@@ -67,7 +67,7 @@ def call(io)
   private
 
   def file_format(box_tree)
-    major_brand = box_tree.find { |box| box.type == 'ftyp' }&.fields[:major_brand]
+    major_brand = box_tree.find { |box| box.type == 'ftyp' }&.fields&.[](:major_brand)
     BRAND_FORMATS[major_brand.downcase] if major_brand
   end
 

spec/parsers/mp4_parser_spec.rb

@@ -31,6 +31,17 @@
       end
     end
 
+    context "when when magic bytes are present but the 'ftyp' box can't be parsed" do
+      let(:io) do
+        input = [0xFF].pack('N') + 'ftyp' + 'avc1 ' + [0x1].pack('N')
+        StringIO.new(input)
+      end
+
+      it 'should be nil' do
+        expect(subject.call(io)).to be_nil
+      end
+    end
+
     Dir.glob(fixtures_dir + '/MP4/valid/video/*.*').sort.each do |path|
       context "for #{path}" do
         let(:result) { subject.call(File.open(path, 'rb')) }