Internet DRAFT - draft-ietf-xrblock-rtcp-xr-video-lc
draft-ietf-xrblock-rtcp-xr-video-lc
XRBLOCK R. Huang
INTERNET-DRAFT Huawei
Intended Status: Standards Track March 30, 2016
Expires: September 30, 2016
RTCP XR Report Block for Loss Concealment Metrics Reporting on
Video Applications
draft-ietf-xrblock-rtcp-xr-video-lc-06
Abstract
This document defines a new RTCP XR Report Block that allows the
reporting of loss concealment metrics for video applications of RTP.
Status of this Memo
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Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . . 3
1.2 Performance Metrics Framework . . . . . . . . . . . . . . . 3
1.3 Applicability . . . . . . . . . . . . . . . . . . . . . . . 3
2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Video Loss Concealment Methods . . . . . . . . . . . . . . . . 4
4 Video Loss Concealment Report Block . . . . . . . . . . . . . . 5
5 SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1 SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . . 9
5.2 Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . . 9
6 Security Considerations . . . . . . . . . . . . . . . . . . . . 9
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
7.1 New RTCP XR Block Type Value . . . . . . . . . . . . . . . . 10
7.2 New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . . 10
7.3 Contact Information for registrations . . . . . . . . . . . 10
8 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1 Normative References . . . . . . . . . . . . . . . . . . . 10
9.2 Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Metrics Represented Using the Template from RFC 6390 . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1 Introduction
Multimedia applications often suffer from packet losses in IP
networks. In order to get a reasonable degree of quality in case of
packet losses, it is necessary to have loss concealment mechanisms at
the decoder. Video loss concealment is a range of techniques to mask
the effects of packet loss in video communications.
In some applications, reporting the information of receivers applying
video loss concealment could give monitors or senders useful
information on application QoE. One example is no-reference video
quality evaluation. Video probes located upstream from the video
endpoint or terminal may not see loss occurring between the probe and
the endpoint, and may also not be fully aware of the specific loss
concealment methods being dynamically applied by the video endpoint.
Evaluating error concealment is important in the circumstance in
estimating the subjective impact of impairments.
This draft defines one new video loss concealment block type to
augment those defined in [RFC3611] and [RFC7294] for use in a range
of RTP video applications. The metrics defined in this draft belong
to the class of transport-related terminal metrics defined in
[RFC6792].
1.1 RTCP and RTCP XR Reports
The use of RTCP for reporting is defined in [RFC3550]. [RFC3611]
defines an extensible structure for reporting using an RTCP Extended
Report (XR). This draft defines a new Extended Report block that is
used as defined in [RFC3550] and [RFC3611].
1.2 Performance Metrics Framework
The Performance Metrics Framework [RFC6390] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Architectures [RFC6792] provides guidelines for reporting
block format using RTCP XR. The XR block type described in this
document are in accordance with the guidelines in [RFC6390] and
[RFC6792].
1.3 Applicability
These metrics are applicable to video applications the video
component of Audio/Video applications using RTP and applying packet
loss concealment mechanisms which are incorporated into the receiving
endpoint to mitigate the impact of network impairments on QoE. For
example, in an IPTV system Set Top Boxes could use this RTCP XR block
to report loss and loss concealment metrics to an IPTV management
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system to enable the service provider to monitor the quality of the
IPTV service being delivered to end users.
2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3 Video Loss Concealment Methods
Video loss concealment mechanisms can be classified into 4 types as
follow:
a) Frame freeze
The impaired video frame is not displayed, instead, the previously
displayed frame is frozen for the duration of the loss event.
b) Inter-frame extrapolation
If an area of the video frame is damaged by loss, the same area from
the previous frame(s) can be used to estimate what the missing pixels
would have been. This can work well in a scene with no motion but can
be very noticeable if there is significant movement from one frame to
another. Simple decoders can simply re-use the pixels that were in
the missing area while more complex decoders can try to use several
frames to do a more complex extrapolation. Another example of a
sophisticated form of inter-frame repair is to estimate the motion of
the damaged region based on the motion of surrounding regions, and
use that to select what part of the previous frame to use for repair.
Some important frames, such as IDR frames, may not depend on any
other frames and may be involved in a scene change. Using inter-frame
extrapolation method to conceal the loss of these frames may not
obtain a quite satisfactory result.
c) Interpolation
A decoder uses the undamaged pixels in the video frame to estimate
what the missing block of pixels should have.
d) Error Resilient Encoding
The sender encodes the message in a redundant way so that receiver
can correct errors using the redundant information. There are usually
two kinds of Error Resilient Encoding: One is that the redundant data
useful for error resiliency performed at the decoder can be embedded
into the compressed image/video bitstream. The other is bit-block
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level encoding, e.g., FEC.
Usually, methods b,c,d are deployed together to provide a
comprehensive loss concealment in some complex decoders, while method
a is relatively independent and may be only applied in some simple
decoders. Moreover, frame freeze method repairs video based on frames
while the other methods repair video based on fine-grained elements,
such as macroblock or bit-block, which will cause the measurement
metrics of frame freeze and the other methods slightly different.
Thus, In this document, we differentiate between frame freeze and the
other 3 concealment mechanisms described.
4 Video Loss Concealment Report Block
This block reports the video loss concealment metrics to complement
the audio metrics defined in [RFC7294]. The report block MUST be sent
in conjunction with the information from the Measurement Information
Block [RFC6776]. Instances of this metric block refer by SSRC to the
separate auxiliary Measurement Information Block [RFC6776]. This
metric block relies on the measurement period in the Measurement
Information Block indicating the span of the report. If the
measurement period is not received in the same compound RTCP packet
as this metric block, this metric block MUST be discarded at the
receiving side. The metrics in this report block are based on
measurements that are typically made at the time that a video frame
is decoded and rendered for playout.
The video loss concealment report block has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=VLC | I | V | RSV | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Impaired Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Concealed Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean Frame Freeze Duration (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MIFP | MCFP | FFSC | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for the Video Loss Concealment Report Block
Block Type (BT): 8 bits
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A Video Loss Concealment Report Block is identified by the
constant VLC.
[Note to RFC Editor: Please replace VLC with the IANA provided
RTCP XR block type for this block.]
Interval Metric Flag (I): 2 bits
This field indicates whether the reported metrics are interval,
cumulative, or sampled metrics [RFC6792]:
I=10: Interval Duration - the reported value applies to the
most recent measurement interval duration between successive
metrics reports.
I=11: Cumulative Duration - the reported value applies to the
accumulation period characteristic of cumulative measurements.
I=01: Sampled Value - this value MUST NOT be used for this
block type.
I=00: Reserved.
Video Loss Concealment Method Type (V): 2 bits
This field is used to identify the video loss concealment method
type used at the receiver. The value is defined as follow:
V=10 - Frame freeze
V=11 - Other Loss Concealment Method
V=01&00 - Reserved
If Frame freeze and other loss concealment method are used
together for the media stream, 2 report blocks, one with V=10 for
frame freeze and one with V=11 for other loss concealment method
SHOULD be compounded together to report the whole concealment
information.
RSV: 4 bits
These bits are reserved for future use. They MUST be set to zero
by senders and ignored by receivers (see Section 4.2 of
[RFC6709]).
block length: 16 bits
This field is in accordance with the definition in [RFC3611]. In
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this report block, it MUST be set to 5 when V=10 and be set to 4
when V=11. The block MUST be discarded if the block length is set
to a different value.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
Impaired Duration: 32 bits
The total time length, expressed in units of RTP timestamp from
the sending side of the reporting block, of video impaired by
transmission loss before applying any loss concealment methods.
Two values are reserved: A value of 0xFFFFFFFE indicates out of
range (that is, a measured value exceeding 0xFFFFFFFD) and a value
of 0xFFFFFFFF indicates that the measurement is unavailable.
Concealed Duration: 32 bits
The total time length, expressed in units of RTP timestamp from
the sending side of the reporting block, of concealed damaged
video pictures on which loss concealment method corresponding to
Video Loss Concealment Method Type is applied.
Two values are reserved: A value of 0xFFFFFFFE indicates out of
range (that is, a measured value exceeding 0xFFFFFFFD) and a value
of 0xFFFFFFFF indicates that the measurement is unavailable.
Mean Frame Freeze Duration: 32 bits
Mean Frame Freeze Duration is the mean duration, expressed in
units of RTP timestamp from the sending side of the reporting
block, of the frame freeze events. The value of Mean Frame Freeze
Duration is calculated by summing the total duration of all frame
freeze events and dividing by the number of events. This metric is
optional. It only exists when Video Loss Concealment Method
Type=10.
Mean Impaired Frame Proportion (MIFP): 8 bits
Mean Impaired Frame Proportion is the mean proportion of each
video frame impaired by loss before applying any loss concealment
method during the interval, expressed as a fixed point number with
the binary point at the left edge of the field. It is calculated
by summing the impaired proportion of each video frame and
dividing by the number of frames during this period. The impaired
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proportion of each video frame is obtained by dividing the number
of missing macroblocks from this video frame by the total
macroblock number of the video frame, which is equivalent to
multiplying the result of the division by 256, limiting the
maximum value to 255 (to avoid overflow), and taking the integer
part.
If a video frame is totally lost, a value of 0xFF SHOULD be used
for the frame when calculating the mean value.
Mean Concealed Frame Proportion (MCFP): 8 bits
Mean Concealed Frame Proportion is the mean proportion of each
video frame to which loss concealment (depicted as "V" in the
definition of "Video Loss Concealment Method Type") was applied
during the interval, expressed as a fixed point number with the
binary point at the left edge of the field. It is calculated by
summing the concealed proportion of each video frame and dividing
by the number of frames during this period. The concealed
proportion of each video frame is obtained by dividing the number
of concealed macroblocks from this video frame by the total
macroblock number of the video frame, which is equivalent to
multiplying the result of the division by 256, limiting the
maximum value to 255 (to avoid overflow), and taking the integer
part.
If a lost video frame is totally concealed, a value of 0xFF and if
there are no concealed macroblocks, a value of 0, SHOULD be used
for the frame when calculating the mean value. For Video Loss
Concealment Method Type=10, each frame covered in the period of
frame freeze is considered to be totally concealed, which means a
value of 0xFF MUST be assigned.
Fraction of Frames Subject to Concealment (FFSC): 8 bits
Fraction of Frames Subject to Concealment is calculated by
dividing the number of frames to which loss concealment (using
Video Loss Concealment Method Type) was applied by the total
number of frames and expressing this value as a fixed point number
with the binary point at the left edge of the field. It is
equivalent to multiplying the result of the division by 256,
limiting the maximum value to 255 (to avoid overflow), and taking
the integer part.
A value of 0 indicates that there were no concealed frame and a
value of 0xFF indicates that the frames in the entire measurement
interval are all concealed.
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Reserved: 8 bits
These bits are reserved for future use. They MUST be set to zero
by senders and ignored by receivers (see Section 4.2 of
[RFC6709]).
5 SDP Signaling
[RFC3611] defines the use of SDP (Session Description Protocol) for
signaling the use of RTCP XR blocks.
5.1 SDP rtcp-xr-attrib Attribute Extension
This session augments the SDP attribute "rtcp-xr" defined in Section
5.1 of [RFC3611] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document.
xr-format =/ xr-vlc-block
xr-vlc-block = "vlc"
5.2 Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in section 5.2 of [RFC3611] for unilateral "rtcp-xr"
attribute parameters applies. For detailed usage of Offer/Answer for
unilateral parameter, refer to section 5.2 of [RFC3611].
6 Security Considerations
It is believed that this RTCP XR block introduces no new security
considerations beyond those described in [RFC3611]. This block does
not provide per-packet statistics, so the risk to confidentially
documented in Section 7, paragraph 3 of [RFC3611] does not apply.
An attacker is likely to put incorrect information in the Video Loss
Concealment reports, which will affect the estimation of video loss
concealment mechanisms performance and QoE of users. Implementers
SHOULD consider the guidance in [RFC7202] for using appropriate
security mechanisms, i.e., where security is a concern, the
implementation SHOULD apply encryption and authentication to the
report block. For example, this can be achieved by using the AVPF
profile together with the Secure RTP profile as defined in [RFC3711];
an appropriate combination of the two profiles (an "SAVPF") is
specified in [RFC5124]. However, other mechanisms also exist
(documented in [RFC7201]) and might be more suitable.
7 IANA Considerations
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New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, please refer
to [RFC3611].
7.1 New RTCP XR Block Type Value
This document assigns the block type value VLC in the IANA "RTP
Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
the "Video Loss Concealment Metric Report Block".
[Note to RFC Editor: please replace VLC with the IANA provided RTCP
XR block type for this block.]
7.2 New RTCP XR SDP Parameter
This document also registers a new parameter "video-loss-concealment"
in the "RTP Control Protocol Extended Reports (RTCP XR) Session
Description Protocol (SDP) Parameters Registry".
7.3 Contact Information for registrations
The contact information for the registration is:
RAI Area Directors
rai-ads@tools.ietf.org
8 Acknowledgements
The author would like to thank Colin Perkins, Roni Even for their
valuable comments.
9 References
9.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)", RFC
3611, November 2003.
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[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC5124] Ott, J., and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, February 2008.
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information
Reporting Using a Source Description (SDES) Item and an
RTCP Extended Report (XR) Block", RFC6776, October 2012.
[RFC7294] Clark, A., Zorn, G., Bi, C. and Q., Wu, "RTCP XR Report
Block for Concealment Metrics Reporting on Audio
Applications", April 2014.
9.2 Informative References
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[RFC6709] Carpenter, B., and S. Cheshire, "Design Considerations for
Protocol Extensions", RFC 6709, September 2012.
[RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", RFC 6792, November 2012.
[RFC7201] Westerlund, M. and C., Perkins, "Qptions for Securing RTP
Sessions", RFC 7201, April 2014.
[RFC7202] Perkins, C. and M., Westerlund, "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, April 2014.
Appendix A. Metrics Represented Using the Template from RFC 6390
a. Video Impaired Duration Metric
* Metric Name: Video Impaired Duration Metric
* Metric Description: The total time length of video impaired by
transmission loss before applying any loss concealment methods.
* Method of Measurement or Calculation: The metric is based on
measurements that are typically made at the time that a video
frame is decoded and rendered for playout.
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* Units of Measurement: This metric is expressed in units of RTP
timestamp.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
* Use and Applications: The metric is applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
applied to the receiving endpoint to mitigate the impact of
network impairments on QoE.
b. Video Concealed Duration Metric
* Metric Name: Video Concealed Duration Metric
* Metric Description: The total time length of concealed damaged
video pictures on which loss concealment method corresponding to
Video Loss Concealment Method Type is applied.
* Method of Measurement or Calculation: The metric is based on
measurements that are typically made at the time that a video
frame is decoded and rendered for playout.
* Units of Measurement: This metric is expressed in units of RTP
timestamp.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
* Use and Applications: These metrics are applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
incorporated into the receiving endpoint to mitigate the impact of
network impairments on QoE.
c. Mean Video Frame Freeze Duration Metric
* Metric Name: Mean Video Frame Freeze Duration Metric
* Metric Description: The mean duration of the frame freeze
events.
* Method of Measurement or Calculation: The metric is based on
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measurements that are typically made at the time that a video
frame is decoded and rendered for playout. The metric is
calculated by summing the total duration of all frame freeze
events and dividing by the number of events.
* Units of Measurement: This metric is expressed in units of RTP
timestamp.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
* Use and Applications: These metrics are applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
incorporated into the receiving endpoint to mitigate the impact of
network impairments on QoE.
d. Mean Impaired Video Frame Proportion Metric
* Metric Name: Mean Impaired Video Frame Proportion Metric
* Metric Description: Mean proportion of each video frame impaired
by loss before applying any loss concealment method during the
interval.
* Method of Measurement or Calculation: The metric is based on
measurements that are typically made at the time that a video
frame is decoded and rendered for playout. It is calculated by
summing the impaired proportion of each video frame and dividing
by the number of frames during this period. The impaired
proportion of each video frame is obtained by dividing the number
of missing macroblocks from this video frame by the total
macroblock number of the video frame, which is equivalent to
multiplying the result of the division by 256, limiting the
maximum value to 255 (to avoid overflow), and taking the integer
part.
* Units of Measurement: This metric is expressed as a fixed point
number with the binary point at the left edge of the field.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
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* Use and Applications: These metrics are applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
incorporated into the receiving endpoint to mitigate the impact of
network impairments on QoE.
e. Mean Concealed Video Frame Proportion Metric
* Metric Name: Mean Concealed Video Frame Proportion Metric
* Metric Description: Mean proportion of each video frame to which
loss concealment (using Video Loss Concealment Method Type) was
applied during the interval.
* Method of Measurement or Calculation: The metric is based on
measurements that are typically made at the time that a video
frame is decoded and rendered for playout. It is calculated by
summing the concealed proportion of each video frame and dividing
by the number of frames during this period. The concealed
proportion of each video frame is obtained by dividing the number
of concealed macroblocks from this video frame by the total
macroblock number of the video frame, which is equivalent to
multiplying the result of the division by 256, limiting the
maximum value to 255 (to avoid overflow), and taking the integer
part.
* Units of Measurement: This metric is expressed as a fixed point
number with the binary point at the left edge of the field.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
* Use and Applications: These metrics are applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
incorporated into the receiving endpoint to mitigate the impact of
network impairments on QoE.
f. Fraction of Video Frames Subject to Concealment Metric
* Metric Name: Fraction of Video Frames Subject to Concealment
Metric
* Metric Description: Proportion of concealed video frames to
which loss concealment (using Video Loss Concealment Method Type)
was applied comparing to the total number of frames during the
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interval.
* Method of Measurement or Calculation: The metric is based on
measurements that are typically made at the time that a video
frame is decoded and rendered for playout. This metric is
calculated by dividing the number of frames to which loss
concealment (using Video Loss Concealment Method Type) was applied
by the total number of frames. It is equivalent to multiplying the
result of the division by 256, limiting the maximum value to 255
(to avoid overflow), and taking the integer part.
* Units of Measurement: This metric is expressed as a fixed point
number with the binary point at the left edge of the field.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: See paragraph 1 of Section 4.
* Use and Applications: These metrics are applicable to video
applications of RTP and the video component of Audio/Video
applications in which packet loss concealment mechanisms are
incorporated into the receiving endpoint to mitigate the impact of
network impairments on QoE.
Authors' Addresses
Rachel Huang
Huawei
101 Software Avenue, Yuhua District
Nanjing 210012
China
EMail: rachel.huang@huawei.com
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