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

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




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


Audio MOS, a 1-5 score that considers the effect of the audio codec, bit rate, sample rate and packet loss on viewing quality


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


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



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



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



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



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



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




Mean Absolute Packet Delay Variation (ITU-T G.1020)


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




Loss of synchronization at MPEG transport layer


Invalid MPEG transport sync byte


Incorrect packet order, duplicate packet or lost packet


Transport error indicator in MPEG transport header set


Discontinuity in program clock reference (PCR)


Time interval between two successive PCR values more than 40ms


Difference between two consecutive PCR values is over 100ms without discontinuity bit set


Interval between presentation time stamps more than 700ms



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. 

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