stagefright: httplive: Decouple block size from bandwidth estimate

A very small block size in PlaylistFetcher can lead to framework
overhead and difficulty streaming high bitrate content, but since
HTTPBase keeps a constant history of the past 100 HTTP reads, the
block size directly affects bandwidth estimation and in turn,
switching latency.

Add setBandwidthHistorySize() to HTTPBase to allow setting the
history size for bandwidth estimation. Call this within LiveSession
based on the current block size to ensure that the number of bytes
used for estimating bandwidth does not change if the block size is
changed in PlaylistFetcher.

Since a single TCP/IP packet can contain up to 64k of data, increase
the block size in PlaylistFetcher from 2k to lcm(188, 1024) or 47k to
avoid inaccuracies in read timings due to up to a comparable 47 reads
from the same locally-cached packet instead of from the network.

Also make HTTPBase::addBandwidthMeasurement() virtual to allow
bandwidth estimation extensions that do not rely on a history list.

Bug: 18821145
Change-Id: I5f957be01f5346e74cfb7eeb150ca4b397ad5798

1 files changed, 4 insertions, 1 deletions

diff --git a/media/libstagefright/include/HTTPBase.h b/media/libstagefright/include/HTTPBase.h
index 1c3cd5e..0c66e27 100644
--- a/media/libstagefright/include/HTTPBase.h
+++ b/media/libstagefright/include/HTTPBase.h
@@ -48,6 +48,8 @@ struct HTTPBase : public DataSource {
 
     virtual status_t setBandwidthStatCollectFreq(int32_t freqMs);
 
+    virtual void setBandwidthHistorySize(size_t numHistoryItems);
+
     static void RegisterSocketUserTag(int sockfd, uid_t uid, uint32_t kTag);
     static void UnRegisterSocketUserTag(int sockfd);
 
@@ -55,7 +57,7 @@ struct HTTPBase : public DataSource {
     static void UnRegisterSocketUserMark(int sockfd);
 
 protected:
-    void addBandwidthMeasurement(size_t numBytes, int64_t delayUs);
+    virtual void addBandwidthMeasurement(size_t numBytes, int64_t delayUs);
 
 private:
     struct BandwidthEntry {
@@ -69,6 +71,7 @@ private:
     size_t mNumBandwidthHistoryItems;
     int64_t mTotalTransferTimeUs;
     size_t mTotalTransferBytes;
+    size_t mMaxBandwidthHistoryItems;
 
     enum {
         kMinBandwidthCollectFreqMs = 1000,   // 1 second