Image for No Reference metrics

No reference metrics

No reference metrics measure the quality of a video by measuring the distortions that may have been generated by the encoding. Therefore, a no reference metric is always dedicated to a particular encoding format.

AccepTV has developped no reference metrics for the two most used encoding formats: the first metric is designed for MPEG-2 whereas the second one is designed for H.264 (MPEG4/AVC).

For each codec, the corresponding metric measures the distortions generated by the encoding:

  • No Reference metric for MPEG-2 video: measurement of blockiness visibility, measurement of blur perception.
  • No Reference metric for H.264 (MPEG-4/AVC) video: measurement of blockiness visibility, measurement of blur perception, measurement of contrast between macroblocs (because of the deblocking filter).

This is essential and makes a great difference with some other existing video quality measurement solutions. Indeed, some of these solutions are designed using one given encoding format, then vendors claim that they work for any format. For example, many solutions are designed for MPEG-2 because they measure the visibility of MPEG-2 artefacts like blockiness and blur (please note that measuring blockiness on MPEG-2 is quite easy since all the blocks have a known location and size). And yet, these solutions are also proposed to measure the quality of videos that have been encoded using H.264 (MPEG-4/AVC). However :

  • using H.264 encoding, the blocks have varied sizes and don't have previously defined locations (so blockiness measurement has to be adapted to H.264)
  • the H.264 decoder contains a deblocking filter (so the main cause of blockiness is packets loss)
  • the main distortion in H.264 encoded videos is not blockiness but is more contrast loss (so the importance given to the different distortions types has to be adapted to each format).

Therefore, you must understand that a video quality metric designed for MPEG-2 must not be used to measure the quality of videos encoded with H.264.

Related product: Video Quality Monitor (get a free evaluation version).