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VCM: Added condition(s) for setting FEC protection factor to zero at low bitrates.

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Review URL: https://webrtc-codereview.appspot.com/494001

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2084 4adac7df-926f-26a2-2b94-8c16560cd09d
This commit is contained in:
marpan@webrtc.org 2012-04-20 16:05:24 +00:00
parent 63a34f4f29
commit 88ad06b999
2 changed files with 41 additions and 1 deletions
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29
src/modules/video_coding/main/source/media_opt_util.cc
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@ -141,6 +141,31 @@ int VCMNackFecMethod::MaxFramesFec() const {
return _maxFramesFec;
}
bool VCMNackFecMethod::BitRateTooLowForFec(
const VCMProtectionParameters* parameters) {
// Bitrate below which we turn off FEC, regardless of reported packet loss.
// The condition should depend on resolution and content. For now, use
// threshold on bytes per frame, with some effect for the frame size.
// The condition for turning off FEC is also based on other factors,
// such as |_numLayers|, |_maxFramesFec|, and |_rtt|.
int estimate_bytes_per_frame = 1000 * BitsPerFrame(parameters) / 8;
int max_bytes_per_frame = kMaxBytesPerFrameForFec;
int num_pixels = parameters->codecWidth * parameters->codecHeight;
if (num_pixels <= 352 * 288) {
max_bytes_per_frame = kMaxBytesPerFrameForFecLow;
} else if (num_pixels > 640 * 480) {
max_bytes_per_frame = kMaxBytesPerFrameForFecHigh;
}
// TODO (marpan): add condition based on maximum frames used for FEC,
// and expand condition based on frame size.
if (estimate_bytes_per_frame < max_bytes_per_frame &&
parameters->numLayers < 3 &&
parameters->rtt < kMaxRttTurnOffFec) {
return true;
}
return false;
}
bool
VCMNackFecMethod::EffectivePacketLoss(const VCMProtectionParameters* parameters)
{
@ -156,6 +181,10 @@ VCMNackFecMethod::UpdateParameters(const VCMProtectionParameters* parameters)
ProtectionFactor(parameters);
EffectivePacketLoss(parameters);
_maxFramesFec = ComputeMaxFramesFec(parameters);
if (BitRateTooLowForFec(parameters)) {
_protectionFactorK = 0;
_protectionFactorD = 0;
}
// Efficiency computation is based on FEC and NACK

13
src/modules/video_coding/main/source/media_opt_util.h
View File

@ -203,6 +203,16 @@ public:
protected:
enum { kUpperLimitFramesFec = 6 };
// Thresholds values for the bytes/frame and round trip time, below which we
// may turn off FEC, depending on |_numLayers| and |_maxFramesFec|.
// Max bytes/frame for VGA, corresponds to ~140k at 25fps.
enum { kMaxBytesPerFrameForFec = 700 };
// Max bytes/frame for CIF and lower: corresponds to ~80k at 25fps.
enum { kMaxBytesPerFrameForFecLow = 400 };
// Max bytes/frame for frame size larger than VGA, ~200k at 25fps.
enum { kMaxBytesPerFrameForFecHigh = 1000 };
// Max round trip time threshold in ms.
enum { kMaxRttTurnOffFec = 200 };
};
@ -219,7 +229,8 @@ public:
bool ProtectionFactor(const VCMProtectionParameters* parameters);
// Get the max number of frames the FEC is allowed to be based on.
int MaxFramesFec() const;
// Turn off the FEC based on low bitrate and other factors.
bool BitRateTooLowForFec(const VCMProtectionParameters* parameters);
private:
int ComputeMaxFramesFec(const VCMProtectionParameters* parameters);