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Andy Quested

Listed below are comments made by Andy Quested between Wednesday, 9th December 2009 and Saturday, 12th December 2009.

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The Hitchhiker's Guide to Encoding: The Salmon of Style (Or how programmes styles can change your view) 7:45pm on 12 Dec 2009 Dear all

I am away for the next few days - will try and post when I have an internet connection but it may be intermittent

Andy
The Hitchhiker's Guide to Encoding: The Salmon of Style (Or how programmes styles can change your view) 11:01am on 12 Dec 2009 Some posts will take a while to answer so this is a quick scan through - I will come back to some of the once I step over

Dear hdblogger Thanks for the post #3. Sorry you feel that way but we have had post suggesting HD should always be sharp
Dear Technogran Thanks for your post #4 - quite interesting it came after hdblogger's comment. We do have programmes that are pin sharp from foreground to background where appropriate (the CIN concert for example) but surely you wouldn't suggests dramas such as Cranford, Wallander and Silent Witness should do the same
Dear Balderdash Thanks for post #7 and Midzone1 #15 - yes I am very proud of the work we have done from the beginning of the BBC's involvement HD to date
Dear Mark Jones thank you for post #9 although I do not comment on other HD channels I do watch then and can say we not only stand up well against them, we exceed the quality many times.
Dear domsmith Thank you for your post #11. You are spot on when you say the technology is still evolving - and it is very quickly. We are looking at various changes to the encoder with the next software upgrade which I hope will start testing very soon
Dear HD1080 #16 and daveac #17 thanks for the comments. At the moment the choice of 25i or 25p lies with a producer (fiction or non), it is not a technical issue. If a producer wanted to give a programme a colour wash or use graduated filters or make a scene in monochrome, as long as it meets the technical requirements for delivery it is an editorial decision signed off by who ever commissioned the programme.

Dear tagmclaren thank you for the comment - re updated can I just refer you to the answer I gave domsmith above?
Dear Mike Bentley and burnlea thank you for your posts - other than day one, the whole blog has been about the PQ in relation to the new encoder. This is common to all programmes and the question I always ask is - has the new encoder affected a programme more to less than the old. In general the answer has been "less" except the comments I made in yesterday's blog about noise.
Dear jtemplar thank you for your post #26. As a multi genre channel we do have to deal with a lot of different programme types and styles. The current technology does not allow us to do VBR at the moment but that does not mean it will never happen. VBR would allow bursts of higher bit rate if the encoder believed it needed it but it would also allocate lower bit rates if it thought it didn't. The question here is, how do we make sure it uses the most appropriate for the picture?

I will come back to the rest later

Andy
The Hitchhiker's Guide to Encoding: The Salmon of Style (Or how programmes styles can change your view) 08:15am on 12 Dec 2009 Dear Squegg
I don't actually have an office - not sure I would know what to do with one! The only elephant I have seen recently is a rather "fetching" ornament my daughter found at a craft fair or something

I talked a bit about motion in the blog and at the moment we don't plan to make motion a technical requirement - quite difficult to do with the volume of programmes using it. But we do try and make programmes use it properly

Andy
The Hitchhiker's Guide to Encoding: The Salmon of Style (Or how programmes styles can change your view) 08:09am on 12 Dec 2009 Dear PixelJunkie (and others)

Thank you for the post. I know several people who can spot things just as you can by the way! PSNR is not perfect and if we had used it alone to asses actual picture quality we would have been seriously at fault. PSNR is one of several methods of measurement and if you work within its limitations it is very useful.. Normally we wouldn’t publish these results as interpreting them can often lead to more questions than the results themselves. But in this case (and because some of the posts had asked for the results) we did because we were making a comparison between two devices using the same codec through the same path. I even used the Wikipedia link that says
"...it is only conclusively valid when it is used to compare results from the same codec (or codec type) and same content…"
Using expert viewers is the primary method of assessment as always

Andyused
The Hitchhiker's Guide to Encoding: The Salmon of Style (Or how programmes styles can change your view) 07:51am on 12 Dec 2009
Dear all - catching up with the comment and in no particular order

Deaf Simon #80 - the encoders are not faulty they do their job but they can be improved. The old coders were no different but did not handle audio in the same way and were always a potential for errors. The mix/fade issue was known about as I said very early on but the overall improvement in coding was still worth doing. I was at BBC R&D yesterday and we should be able to start testing the fix very soon (have a look at the first blog re what has to be tested)

Andy
The Hitchhiker's Guide to Encoding: And Another Test...(Or PSNR and all that...) 11:33pm on 11 Dec 2009 Sorry Paul

May be too many tomorrows - I meant I would reply to the Friday blog comments tomorrow. I have just had a quick scan through and I have too many comments to start now!

Andy
The Hitchhiker's Guide to Encoding: And Another Test...(Or PSNR and all that...) 11:19pm on 11 Dec 2009 Dear all (again)

I will move on to Friday's blog tomorrow - too late now and it's my turn to shut the rabbits in
The Hitchhiker's Guide to Encoding: And Another Test...(Or PSNR and all that...) 10:33pm on 11 Dec 2009 Dear all - meetings went on far too long and through today...
I thought I would do a couple of big posts covering several questions at a time - also will carry over answers into tomorrow. Apologies fir spelling and grammar

A couple of things first re the press. We have not closed off blogs to prevent comment. There has ALWAYS been another blog carrying on the discussion. Also after about 500 posts they get to big to track properly for you and me. I am more than happy to carry on the discussions and (as fair notice) when I get to the bottom of this blog I will concentrate answers in the next. I can keep scanning the others for new posts but may miss some. Also as this is a series and tomorrow is the last, I don’t consider any PQ post to be off topic
I would like to make one house rule - I will not call anyone a geek - as long as no one gives themselves the title!
Second general point - BBC HD of Virgin. Several blogs ago (and even pre this series) I said we don't do the encoding for the Virgin platform. The signal from the playout and continuity area goes straight to an inject point somewhere in the bottom of Television Centre and (I assume) off to Virgin's distribution centre. The Virgin distributed HD signal MPEG2 at around 17Mbs and has been for sometime. In fact I believe there has only been one encoder change since the test channel launched. MPEG2 is a mature codec so updates (hard and soft) don't come along very often.
So to the post
Dear bob - I would love to but to do PSNR tests you need access to the pre encoded material and I'm not sure we could do that!
Dear Mo - the playout server is the common point in the chain. Just about every non live programme is played out from the server. The server uses MPEG2 100Mbs I-Frame. This may change in the future to an MPEG4 AVC codec.
Dear IanMac1 - This series of blogs is an in depth look at some of the processes we use to get the channel on-air. We didn't just want to say "tests show the quality hasn't changed" Not sure what you mean by PR exercise though as we have just told you what we have done.
Dear hdblogger - If I'm correct, what you are saying is the new encoders are showing up noise more because they are more sensitive right?" - not more sensitive - but better at passing on the source.
Dear Midzone1 - I have never hidden behind "smoke and mirrors", I think we have been very open and honest in these blogs and I have persuaded people to share far more information that they normally would.
Dear Easybourne and fridaysboy - I will save this till tomorrow's blog but if I forget please remind me.

Dear HD1080 & Simon Loach & burnlea - the test method was discussed in yesterdays blog at the distances generally used for expert viewing. The PSNR and eyeball assessments included EBU and BBC material. The EBU material is designed to stress encoders to show coding errors without noise and other codec (both of which are variables) getting in the way of the results. But real programme material is used because we transmit a real channel!!
One important point though, the test were primarily comparison tests i.e. was the new coder as good as the old over a range of material.
Dear burnlea.& dpgs400 Forgive me for not answering here - the question list keep growing and changing. I will try to answer the latest version in tomorrows posts
Dear tagmclaren The mix/fade issue was probably the only reason the new encoder didn’t show a larger PQ improvement BUT it is there and it is a distraction and it will be improved

Dear rwgladwin We are discussing this in the blogs and I do read every post (sometimes a few days late though). We have acknowledged the mix/fade problem that does cause picture degradation and are working to fix it as soon as possible..

Dear trevorjharris you are indeed correct and we are looking at other methods. At the moment we use PSNR because although it may have inconsistencies with eyeballs, we do know it's short comings.

Dear speedwayfan22 thanks for the comment. I do believe we have a first rate channel - we do have problems and it's my job to get rid of as many as possible and I will continue to do so

Dear rmgalley & PixelJunkie The key to quality is good processing (encoding tools) and clean pictures. We are testing the next version of software that should minimise the mix/fade issues and improve the noise handling of the encoder. I would rather have no noise than noise reproduced faithfully but that may take some time and much persuasion

Dear citizenloz - sorry you think it's "Pointless obfuscation in an attempt to blind us with science" The blogs are a straight forward report of the processes we go through to test encoders and the results
Dear GarySargent. Both encoders were tested and measured against the playout server The old encoder was tested at 16Mbs with the same setting used for transmission.. The target was to achieve the same quality.

Dear digitalscoobiedoo #41 - I covered this document in the EBU episode

Dear Andy Hampshire the professional decoder is there to turn the output of the encoder into the same SDI signal as the input. As this happens for both encoders it removes the STB variable i.e. allows a more accurate measurement of the effect of encoding

Dear digitalscoobiedoo I talked about screen shots in Monday's post. Re your post 53 the target was to make sure the new encoder was capable of delivering at least the same quality as the old over a wide range of material (including test sequences). Having established this as a benchmark we can (and are always) trying to improve quality. As has been said in all the news paper article the old encoders were not going to get any better - there would be no further upgrades.

Dear mikerb Current MPEG4 (AVC) encoders are about twice as efficient as MPEG2. The old encoder was doing it's best but as I said to digitalscoobiedoo it was going to do no more. At least your cat thinks it's OK!!

Dear SkyCaddie we hope a software update will be sent to use soon and we can start testing.
The Hitchhiker's Guide to Encoding: And Another Test...(Or PSNR and all that...) 11:47pm on 10 Dec 2009 Dear all - only just back so no chance to read all the posts. Will look tomorrow and post some replies. On a quick scan though I have one thing to add here.

The tests were comparison tests between the new and old encoders. The material on the playout server was used as the reference. As they were comparison tests the results only show the differences between the two encoders.

Andy
The Hitchhiker's Guide to Encoding: Mostly Testing (Or how to set up an encoder test) 11:40pm on 09 Dec 2009 Dear wednesday83, thank you for the post - can I refer you to post 31

Andy

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