Re: [xrblock] Loss-Type concealment vs Buffer adjustment type concealment

Re: [xrblock] Loss-Type concealment vs Buffer adjustment type concealmentHi, Alan:
That's a good summary for video loss concealment method.
Please see my comments inline.
  ----- Original Message ----- 
  From: Alan Clark 
  To: Qin Wu 
  Cc: xrblock@ietf.org 
  Sent: Wednesday, October 10, 2012 5:02 PM
  Subject: Re: [xrblock] Loss-Type concealment vs Buffer adjustment type concealment

  Qin

  The wording in draft-ietf-xrblock-xr-consec-.. is definitely related to audio. Video does have loss concealment and there are a range of methods used, for example:

  (i) Frame freeze
  In this case the impaired video frame is not displayed and the previously displayed frame is hence "frozen" for the duration of the loss even

[Qin]: Agree, this method is also widely used technique in the IPTV deployment or cable TV deployment.

  (ii) 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 may simply re-use the pixels that were in the missing are, more complex decoders may try to use several frames to do a more complex extrapolation

[Qin]: I think one example of inter-frame extrapoltion is motion-compensated repetition. Motion-compensated repetition is widely used techniques for video loss concealment
and is used a repeat of the preceding frame to replace the part of the frame affected by the loss when loss occur.

(iii) Interpolation
A decoder may use the undamaged pixels in the image to estimate what the missing block of image should have

[Qin]: Two examples of interpolation are repair in the spatial domain and repair in the frequency domain
Repair in the spatial domain means relying on interpolation of a missing block, on the basis of the surrounding data. 
For example, the average pixel color for each of the surrounding blocks can be calculated, and the missing block can be set to the average of those colors. 
 The similar techiques used in repair in the spatial domain can be applied to repair in the frequency domain.For example, for codecs based on the DCT, 
such as MPEG, H.261, and H.263. The low-order DCT coefficients can be averaged across the surrounding blocks, to generate a fill-in for a missing block.

(iv) Noise insertion
A decoder may insert random pixel values - which would generally be less noticeable than a blank rectangle in the image

[Qin]: It looks to me Noise insertion also can be regarded as one kind of interpolation. At least, they have the similarity.
For example,when interpolation using repair in the spatial domain, the average pixel color for each of the surrounding blocks is calculated to replace the missing block.
In the Noise insertion, a random pixel color value is choosen for the missing block.

Alan

On 10/10/12 3:41 AM, "Qin Wu" <bill.wu@huawei.com> wrote:

    Hi,
    In draft-ietf-xrblock-rtcp-xr-concsec,concealment is splitted into two type of concealments.
    One is Loss-Type concealment and the other is Buffer adjustment type concealment.
    So the question is are these two type of concealments applied to video? If the answer is yes,
    how to take video loss concealment into account? Since in the current draft, when we define
    Loss-type concealment and buffer adjustment type concealment, only audio loss concealment 
    is considered. See section 2.2 of draft-ietf-xrblock-rtcp-xr-concsec below for defintions of loss-type concealment
    and buffer adjustment type concealment:
    "    
         Loss-type concealment is reactive insertion or deletion of samples
          in the audio playout stream due to effective frame loss at the
          audio decoder.  "Effective frame loss" is the event in which a
          frame of coded audio is simply not present at the audio decoder
          when required.  In this case, substitute audio samples are
          generally formed, at the decoder or elsewhere, to reduce audible
          impairment.

         Buffer Adjustment-type concealment is proactive or controlled
          insertion or deletion of samples in the audio playout stream due
          to jitter buffer adaptation, re-sizing or re-centering decisions
          within the endpoint. Because this insertion is controlled, rather than occurring
          randomly in response to losses, it is typically less audible than
          loss-type concealment.  For example, jitter buffer adaptation
          events may be constrained to occur during periods of talker
          silence, in which case only silence duration is affected, or
          sophisticated time-stretching methods for insertion/deletion
          during favorable periods in active speech may be employed.  For
          these reasons, buffer adjustment-type concealment MAY be exempted
          from inclusion in calculations of Concealed Seconds and Severely
          Concealed Seconds.
    "

    Regards!
    -Qin 

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