stagefright: fix issues with bitrate handling

- parse btrt mp4 box
- write max and avg. bitrates into avcc
- fix the use of "bit-rate" vs. the correct "bitrate"
- document ESDS better
- fix some spacing

Bug: 28671284
Change-Id: I94961a095c6d162af38b7999cc946f899a1b1b09
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
index 4ae8e82..e59a498 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
+++ b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
@@ -1770,7 +1770,7 @@
                     mime.c_str(), audioFormat);
 
             int avgBitRate = -1;
-            format->findInt32("bit-rate", &avgBitRate);
+            format->findInt32("bitrate", &avgBitRate);
 
             int32_t aacProfile = -1;
             if (audioFormat == AUDIO_FORMAT_AAC