Diagnosing Problems in IP Video Systems

Gaps in Playout

Buffer starvation in TCP based systems

When server congestion or packet loss occurs, there is an insufficient flow of packets into the playout buffer in the set top box.  This will result in playout being paused while the buffer is refilling.  Typical gaps may range from 5-20 seconds.

Excessive packet loss in UDP based systems

Packet loss can occur in bursts. If the burst density is high then the image will be severely degraded.  Some playback systems/ decoders will simply output a blank image rather than a severely degraded image (see also Frame Freeze).

Frame Freeze

Excessive packet loss in UDP based systems

Packet loss can occur in bursts. If the burst density is high then the image will be severely degraded.  Some playback systems/ decoders will simply output the last good image rather than a severely degraded or blank image (see also Gaps in Playout).

Blockiness

Packet loss in UDP based systems

Packet loss will result in some of the blocks (macroblocks) within the image being corrupted, which leads to visible blocks within the image.  Low rates of loss will result in occasional blocks in different parts of the image whereas very high rates of loss will cause extensive degradation and frame freezes.

Transcoding errors

Transcoding errors can lead to blocks of mis-colored pixels appearing within the image.  These could be due to read errors from disk drives or magnetic tape, or to transmission errors between the video source and the transcoding system.

High rate of compression

High rates of compression will result in the block structure of the image being visible.  This will generally persist throughout a video sequence at a fairly constant level.

Image noise

Edge noise

Noise around sharp edges in the image may be edge noise or mosquito noise.  This is typically due to the compression level being too high.

Quantization noise

Quantization noise will appear as overall degradation of the image and is due to the use of coarse quantization within the encoding process.

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