Telchemy Video Quality Metrics
Telchemy video quality metrics are grouped into key layers – Perceptual Quality Metrics, Video Stream Metrics and Transport Metrics.
- Perceptual Quality Metrics provide high level Video and Audio Quality of Experience (QoE) scores, giving immediate visibility of the impact of a wide range of impairments on user perceived quality
- Video Stream Metrics provide essential visibility into the performance and configuration of the encoded video stream.
- Transport Metrics provide key information on performance of IP, UDP, FEC, RTP and MPEG transport protocols, which are typically the major source of transient video quality problems.
Perceptual Quality Metrics
These metrics provide high level QoS scores for Video, Audio and overall quality, giving immediate visibility of the impact of a wide range of impairments. Telchemy’s technology is unique in its ability to model the impact of transient IP problems on user perceived quality.
|
Perceptual Quality Metrics |
|
|
Metric |
Description |
|
MOS-V |
Video MOS, a 1-5 score that considers the effect of the video codec, frame rate, packet loss distribution and GoP structure on viewing quality |
|
MOS-A |
Audio MOS, a 1-5 score that considers the effect of the audio codec, bit rate, sample rate and packet loss on viewing quality |
|
MOS-AV |
Audiovisual MOS – a 1-5 score that considers the effect of picture & audio quality and audio-video synchronization on overall user experience |
|
Video Service Transmission Quality (VSTQ) |
Transmission quality, a 0-50 codec independent score measuring the ability of the IP network to carry reliable video |
|
Gap MOS-V |
Picture quality during “good” periods when little or no degradation is occurring |
|
Burst MOS-V |
Picture quality during “bad” periods when significant degradation is occurring |
|
Estimated PSNR (EPSNR) |
Estimated Peak Signal to Noise Ratio (PSNR) expressed in dB. This is an estimate of the distortion that has occurred between the source video stream and the output video stream. |
|
Degradation Factors |
0-10 scores indicating severity of degradation in quality due to (each of) packet loss, jitter, codec type, audio-video sync, delay and recency of burst packet loss |
Video Stream Metrics
The Video Stream Description provides information on the type of codec being used, Group of Pictures structure and length, image size and other key factors.
|
Video Stream Description |
|
|
Metric |
Description |
|
Codec type |
Type of codec (e.g. MPEG4) |
|
GoP type |
Group of Pictures type (e.g. IBBP…) |
|
Minimum GoP length |
Minimum number of frames in Group of Pictures |
|
Maximum GoP length |
Maximum number of frames in Group of Pictures |
|
Average inter-I frame gap |
Average number of P and B frames between I frames |
|
Image size |
Image size in pixels (X x Y) (autodetected *) |
Video Stream Metrics provide insight into the proportion of different type of video frame that are impacted by packet loss and discard, and to the overall video bandwidth.
|
Video Stream Metrics |
|
|
Metric |
Description |
|
Proportion of I frames impaired |
Percentage of I frames impaired by loss/discard |
|
Proportion of P frames impaired |
Percentage of P frames impaired by loss/discard |
|
Proportion of B frames impaired |
Percentage of B frames impaired by loss/discard |
|
I, P, B frame packets received |
Counts of the numbers of I, P and B frame packets received |
|
I, P, B frame packets lost |
Counts of the numbers of I, P and B frame packets |
|
I, P, B frame packets discarded |
Counts of the numbers of I, P and B frame packets |
|
Mean bandwidth |
Average video bandwidth excluding IP overhead, FEC and retransmissions |
|
Peak bandwidth |
Peak video bandwidth excluding IP overhead, FEC and retransmissions |
Transport Metrics
Packet Loss Metrics provide essential data on IP packet loss before and after the effects of error correction (such as FEC or Reliable UDP). Burst and gap statistics provide valuable insight into the time distribution of lost and discarded packets.
|
Packet Loss Metrics |
|
|
Metric |
Description |
|
Uncorrected Packet Loss Rate |
Percentage of IP packets lost in the network |
|
Corrected Packet Loss Rate |
Packet loss rate after correction by Forward Error Correction or retransmission |
|
Packet Discard Rate |
Percentage of packets discarded due to late arrival |
|
Out of Sequence Packet Rate |
Percentage of packets arriving out of sequence |
|
Duplicate Packet Rate |
Percentage of duplicate packets |
|
Burst Loss Rate |
Percentage of packets lost within burst periods |
|
Burst Length |
Average length of burst periods |
|
Gap Loss Rate |
Percentage of packets lost within gap periods |
|
Gap Length |
Average length of gaps between bursts |
Forward Error Correction can replace lost packets however carries some overhead. The FEC metrics provide a measure of the effectiveness of FEC if used, and provide information on optimum FEC configuration independently of whether FEC is in use or not (allowing service providers to assess whether FEC would be useful).
|
FEC Metrics |
|
|
Metric |
Description |
|
FEC Effectiveness |
Percentage improvement in packet loss rate due to Forward Error Correction |
|
Optimum FEC Block Size |
Optimum FEC block size (packets) |
|
Optimum FEC Correctable Packets |
Optimum number of correctable packets within a block |
Reliable UDP metrics provide insight into the performance of retransmission based protocols such as Reliable UDP. These protocols improve packet loss rate but increase the variability of bandwidth.
|
Reliable UDP Metrics |
|
|
Metric |
Description |
|
Proportion of packets retransmitted |
Percentage of packets retransmitted |
|
Ratio of peak to mean bandwidth |
Ratio of bandwidth peak due to retransmission to average bandwidth |
Jitter and Delay metrics provide a view of the impact of deliberate packet smoothing/ rate shaping and network congestion on overall delay and delay variation.
|
Jitter and Delay Metrics |
|
|
Metric |
Description |
|
MAPDV |
Mean Absolute Packet Delay Variation (ITU-T G.1020) |
|
PPDV |
Packet to Packet Delay Variation (RFC3550) |
|
Round trip delay |
Round trip delay |
TR101 290 metrics provide information on certain key error types that occur with MPEG Transport protocols, and are useful in identifying and resulting these error conditions.
|
TR 101 290 MPEG Metrics |
|
|
Metric |
Description |
|
TS_sync_loss |
Loss of synchronization at MPEG transport layer |
|
Sync_byte_error |
Invalid MPEG transport sync byte |
|
Continuity_count_error |
Incorrect packet order, duplicate packet or lost packet |
|
Transport_error |
Transport error indicator in MPEG transport header set |
|
PCR_error |
Discontinuity in program clock reference (PCR) |
|
PCR_repetition_error |
Time interval between two successive PCR values more than 40ms |
|
PCR_discontinuity_indicator_error |
Difference between two consecutive PCR values is over 100ms without discontinuity bit set |
|
PTS_error |
Interval between presentation time stamps more than 700ms |
Summary
Telchemy’s video quality metrics provide a rich set of performance and diagnostic information that allows service providers to instantly understand their subscribers’ Quality of Experience and rapidly identify key factors impacting quality.
Conditions of use: The material on this site is copyright Telchemy and may be freely used but not copied or downloaded. In making use of this site the user acknowledges that Telchemy or Contributor has no liability for any issues or problems that may arise directly or indirectly as a result of such use. Telchemy and Contributor are providing this material as-is with no warranty as to correctness or completeness and do not accept any responsibility for any issues or problems of any nature whatsoever that may arise from the use of the material on this site.