Cast: Limit number of events/packets in EncodingEventSubscriber protos.

media/cast/logging/encoding_event_subscriber.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_CAST_LOGGING_ENCODING_EVENT_SUBSCRIBER_H_
 #define MEDIA_CAST_LOGGING_ENCODING_EVENT_SUBSCRIBER_H_
 
 #include <map>
 
 #include "base/memory/linked_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "media/cast/logging/logging_defines.h"
 #include "media/cast/logging/proto/raw_events.pb.h"
 #include "media/cast/logging/raw_event_subscriber.h"
 
 namespace media {
 namespace cast {
 
 typedef std::map<RtpTimestamp,
                  linked_ptr<media::cast::proto::AggregatedFrameEvent> >
     FrameEventMap;
 typedef std::map<RtpTimestamp,
                  linked_ptr<media::cast::proto::AggregatedPacketEvent> >
     PacketEventMap;
 
+// Number of packets per frame recorded by the subscriber.
+// Once the max number of packets has been reached, incoming events will be
+// discarded.
+const int kMaxPacketsPerFrame = 64;

[Alpha Left Google, 2014/04/17 22:59:00]

This number seems small. Why is this 64? Instead of dropping events can we log
with an extra protobuf?

[imcheng, 2014/04/18 00:05:31]

How often will we have more than 64 packets per frame? What number would you
suggest?

I would rather keep it simple and just pick a max number here.

[Alpha Left Google, 2014/04/21 18:14:04]

Sometimes this can happen. A scene change frame can be large (~100kb). Plus
retransmission there can be many more. 

[imcheng, 2014/04/22 01:17:39]

ACK.

On 2014/04/21 18:14:04, Alpha wrote:

+// Number of events per proto recorded by the subscriber.
+// Once the max number of events has been reached, incoming events will be
+// discarded.
+const int kMaxEventsPerProto = 16;

[Alpha Left Google, 2014/04/17 22:59:00]

Why is this 16? It seems small..

[imcheng, 2014/04/18 00:05:31]

How about 32? Normally a proto will rarely have more than 10 events. The only
events that would repeat are retransmission and rtcp events (to a limited
extent).

[Alpha Left Google, 2014/04/21 18:14:04]

I don't see much value in this limit. This limits the types of events in a proto
right? If the most common event type is packet event then having this value
isn't very useful I think.

[imcheng, 2014/04/22 01:17:39]

This limits the number of events, this helps keep individual protos down in
size, when there are a lot of retransmit events for the same packet.

On 2014/04/21 18:14:04, Alpha wrote:

+
 // A RawEventSubscriber implementation that subscribes to events,
 // encodes them in protocol buffer format, and aggregates them into a more
 // compact structure.
 class EncodingEventSubscriber : public RawEventSubscriber {
  public:
   // |event_media_type|: The subscriber will only process events that
   // corresponds to this type.
   // |max_frames|: How many events to keep in the frame / packet map.
   // This helps keep memory usage bounded.
   // Every time one of |OnReceive[Frame,Packet]Event()| is
@@ skipping 48 matching lines @@
   // Set to RTP timestamp of first event encountered after a |Reset()|.
   RtpTimestamp first_rtp_timestamp_;
 
   DISALLOW_COPY_AND_ASSIGN(EncodingEventSubscriber);
 };
 
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_LOGGING_ENCODING_EVENT_SUBSCRIBER_H_