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..9a7822e5ff51e72e77f1b283a8b16442623688c6 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 {
@@ -123,7 +125,8 @@ void FFmpegGlue::InitializeFFmpeg() {
 }
 
 FFmpegGlue::FFmpegGlue(FFmpegURLProtocol* protocol)
-    : open_called_(false) {
+    : open_called_(false),
+      protocol_(protocol) {
   InitializeFFmpeg();
 
   // Initialize an AVIOContext using our custom read and seek operations.  Don't
@@ -155,6 +158,22 @@ 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.
+  int64 pos;
+  scoped_ptr<uint8[]> buffer(new uint8[8192]);
+
+  protocol_->GetPosition(&pos);

[acolwell GONE FROM CHROMIUM, 2013/05/18 01:22:09]

nit: I think you can use avio_context_->opaque to retrieve the protocol pointer.
It might be better to do that instead so protocol_ and avio_context_ can't get
out of sync.

It might even be worth using avio_tell(), avio_seek(), and avio_read() here so
you don't even have to worry about FFmpegURLProtocol.

[jrummell, 2013/05/22 18:27:39]

Done.

+  protocol_->SetPosition(0);
+  int numRead = protocol_->Read(8192, buffer.get());
+  protocol_->SetPosition(pos);
+  if (numRead > 0) {
+    // < 0 means Read failed
+    container_names::FFmpegContainerName container =
+        container_names::DetermineContainer(buffer.get(), 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;