Only run container name detection upon ffmpeg parse failure.

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 77cf6700868cd63c442e5b87e3cabc2c856cd902..c1a2145d4c1f343635b884861d9a45c8ad0f0eb7 100644
--- a/media/filters/ffmpeg_glue.cc
+++ b/media/filters/ffmpeg_glue.cc
@@ -137,25 +137,63 @@ 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.
-  std::unique_ptr<std::vector<uint8_t>> buffer(new std::vector<uint8_t>(8192));
-
-  int64_t 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 nullptr 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_, nullptr, nullptr, nullptr) == 0;
+  const int ret =
+      avformat_open_input(&format_context_, nullptr, nullptr, nullptr);
+
+  // If FFmpeg can't identify the file, read the first 8k and attempt to guess
+  // at the container type ourselves. This way we can track emergent formats.
+  // Only try on AVERROR_INVALIDDATA to avoid running after I/O errors.
+  if (ret == AVERROR_INVALIDDATA) {
+    std::vector<uint8_t> buffer(8192);
+
+    const int64_t pos = AVIOSeekOperation(avio_context_->opaque, 0, SEEK_SET);
+    if (pos < 0)
+      return false;
+
+    const int num_read =
+        AVIOReadOperation(avio_context_->opaque, buffer.data(), buffer.size());
+    if (num_read < container_names::kMinimumContainerSize)
+      return false;
+
+    UMA_HISTOGRAM_SPARSE_SLOWLY(
+        "Media.DetectedContainer",
+        container_names::DetermineContainer(buffer.data(), num_read));
+    return false;
+  } else if (ret < 0) {
+    return false;
+  }
+
+  // Rely on ffmpeg's parsing if we're able to succesfully open the file.
+  container_names::MediaContainerName container =
+      container_names::CONTAINER_UNKNOWN;
+  if (strcmp(format_context_->iformat->name, "mov,mp4,m4a,3gp,3g2,mj2") == 0)

[jrummell, 2017/04/17 18:00:15]

Too bad there isn't a better way to compute this without comparing strings.

[DaleCurtis, 2017/04/17 19:08:46]

Yeah, hence all the test cases to make sure we still match, wish they had an
enum instead for this :( Not sure why they decided not to have one for formats
while having one for codecs.

+    container = container_names::CONTAINER_MOV;
+  else if (strcmp(format_context_->iformat->name, "flac") == 0)
+    container = container_names::CONTAINER_FLAC;
+  else if (strcmp(format_context_->iformat->name, "matroska,webm") == 0)
+    container = container_names::CONTAINER_WEBM;
+  else if (strcmp(format_context_->iformat->name, "ogg") == 0)
+    container = container_names::CONTAINER_OGG;
+  else if (strcmp(format_context_->iformat->name, "wav") == 0)
+    container = container_names::CONTAINER_WAV;
+  else if (strcmp(format_context_->iformat->name, "aac") == 0)
+    container = container_names::CONTAINER_AAC;
+  else if (strcmp(format_context_->iformat->name, "mp3") == 0)
+    container = container_names::CONTAINER_MP3;
+  else if (strcmp(format_context_->iformat->name, "amr") == 0)
+    container = container_names::CONTAINER_AMR;
+  else if (strcmp(format_context_->iformat->name, "avi") == 0)
+    container = container_names::CONTAINER_AVI;
+  // TODO(jrummell): Remove GSM detection. http://crbug.com/711774
+  else if (strcmp(format_context_->iformat->name, "gsm") == 0)
+    container = container_names::CONTAINER_GSM;
+
+  DCHECK_NE(container, container_names::CONTAINER_UNKNOWN);
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Media.DetectedContainer", container);
+
+  return true;
 }
 
 FFmpegGlue::~FFmpegGlue() {