[SBE] The life of a spot after DG sends it to you...

[Henry M. Seiden]

As everyone suggested, the path taken decoding and in retransmitting  
as baseband via satellite (as detailed by Ryan, if that's really what  
happened), then re-encoding may have been the final straw causing huge  
potential for artifacts.

Regardless of how it happened, without careful control of the  
distribution of commercial and program content, electronic relay of  
material is not without flaw.

Henry
On May 20, 2009, at 20:41 , Chris Spacone wrote:


> CBS may have pulled the spot from the SpotBox (it is just a Windows  

> box) and

> transcoded (perhaps using something like FlipFactory) it to the file  

> format

> used on by their video server. Poorly configured FF, low bitrates  

> and a host

> of other problems could account for the artifacts. Consider that the  

> local

> station that actually played the spot OTA may well have done something

> similar to the spot.

>

> As the source material undergoes multiple ingest / encodes / transcode

> operations something called concatenation errors begin to creep in.

> Essentially the quantization step reduces the 'dynamic range' (for  

> lack of a

> better way to describe it) of the video signal which can result in  

> blocky

> artifacts. These become more and more pronounced as the material  

> undergoes

> multiple passes. Quantization problems are clearly seen with the  

> very low

> bitrate video delivered by satellite services. If you watch a black  

> field

> you can see 'rings' or contours where the black jumps from one value  

> to

> another instead of being smoothly continuous. Another error  

> introduced is

> motion artifacting. As each frame of video is analyzed by the  

> encoder a

> series of decisions are made that determine how much of the picture  

> can be

> thrown away and how much should be kept. Motion vectors from frame  

> to frame

> are calculated and a series of MPEG I, P and B frames are generated  

> as part

> of a GOP (Group Of Pictures).

>

> These artifacts can become quite obvious when the material has lots  

> of very

> small type / detail. If you can pause the playback and check  the  

> edges of

> vertical and horizontal elements you will see a sort of 'noise' (I  

> have

> heard it called mosquito noise). This noise is directly related to the

> amount of quantization being applied to the video.

>

> But all of this is speculation and partly lecture; unless you know the

> precise chain the material took along each of the steps you are stuck

> guessing. It is possible to 'objectively' measure the end result  

> against the

> source material and quantify the underlying impairments by using PQA

> testing. Again, all this helps to do is objectively determine if  

> there is a

> problem, not precisely where it was introduced (or worse yet how to  

> fix it).

>

> Chris Spacone

>

>

>

> -----Original Message-----

> From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of  

> Ryan

> Salazar

> Sent: Wednesday, May 20, 2009 12:12 PM

> To: sbe member discussion mail list

> Subject: [SBE] The life of a spot after DG sends it to you...

>

> Everyone,

>

> I figured this would be the best place for me to ask this question...

>

> We send spots (post production facility), to DG Fast Channel via  

> automation.

> DG always tells us the spots look great, in fact, better than most  

> spots

> they receive. They then send the spot to stations via their "Spotbox".

>

> Recently, we had an instance where they sent a spot to CBS-National.  

> CBS

> then fed the spot live via satellite to a local station. That local  

> station

> then fed it to the viewers. We received a complaint that the spot was

> pixelated and blurry. I will admit, our disclaimers were way to  

> small, but

> we had strange artifacting that we don't normally have an issue  

> with. I also

> saw a considerable amount of blocks on the screen during fast  

> movement of

> graphics. I've seen this before after files were converted over and  

> over.

>

> I assume this is because of all the levels the file went through. Us  

> to DG,

> DG to CBS. Then, CBS via Satellite to the station and the station

> broadcasts.

>

> Any ideas? I know I can't really control all the points, but want to  

> see

> what else I can come up with.

>

> Thanks!

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Techworks Professional Systems, Inc. Henry M. Seiden, Founder
henry<at>techworkspro<dot>com