Add UMA stats for audio/video containers.

media/filters/ffmpeg_glue.cc

Index: media/filters/ffmpeg_glue.cc
diff --git a/media/filters/ffmpeg_glue.cc b/media/filters/ffmpeg_glue.cc
index e3b227b2ac5140f74f9057090d0bafdb26429961..c74b0654e9983525dac71216df568ae0c1327c1e 100644
--- a/media/filters/ffmpeg_glue.cc
+++ b/media/filters/ffmpeg_glue.cc
@@ -6,7 +6,9 @@
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/synchronization/lock.h"
+#include "media/base/container_names.h"
 #include "media/ffmpeg/ffmpeg_common.h"
 
 namespace media {
@@ -155,6 +157,22 @@ bool FFmpegGlue::OpenContext() {
   // destruction path to avoid double frees.
   open_called_ = true;
 
+  // Attempt to recognize the container by looking at the first few bytes of the
+  // stream. The stream position is left unchanged.
+  scoped_ptr<std::vector<uint8> > buffer(new std::vector<uint8>(8192));
+
+  int64 pos = AVIOSeekOperation(avio_context_.get()->opaque, 0, SEEK_CUR);
+  AVIOSeekOperation(avio_context_.get()->opaque, 0, SEEK_SET);
+  int numRead = AVIOReadOperation(
+      avio_context_.get()->opaque, buffer.get()->data(), buffer.get()->size());
+  AVIOSeekOperation(avio_context_.get()->opaque, pos, SEEK_SET);
+  if (numRead > 0) {
+    // < 0 means Read failed
+    container_names::MediaContainerName container =
+        container_names::DetermineContainer(buffer.get()->data(), numRead);
+    UMA_HISTOGRAM_SPARSE_SLOWLY("Media.DetectedContainer", container);
+  }
+
   // By passing NULL for the filename (second parameter) we are telling FFmpeg
   // to use the AVIO context we setup from the AVFormatContext structure.
   return avformat_open_input(&format_context_, NULL, NULL, NULL) == 0;