Quality of downconversion to SD in editing?

[Ola Christoffersson]

I am still waiting for my camera so I have lots of time to spend on thinking and trying things out in my head and with the few EX1-clips I have access to. One thing that has worried me is how to be able to produce good masters in SD-quality. When I started my investigations on the EX1 I was comforted reading about how easy it would be to downconvert HD to SD in your editor with potentially better result than if it was shot in SD in the first place.

I have now been experimenting some and I'm starting to get worried again. I am using Avid Media Composer 2.7.7. I have some SP 1080i50 material that I have transcoded to PAL50i and something seems to be wrong. It does not have the same crisp quality that original PAL50-material has and I can also see a disturbing blocky pattern in the fine details. Almost like moaire.
This is still very unscientific but nevertheless I would be very interested in hearing about all you others experiences on this matter. Especially with Avid. What is the quality of the transcoding in Avid?
In theory I realise downconverted HDV should be as good as or better than DV but how do I achieve this in the best way?
Is it better to transcode outside the editing software in Canopus Procoder or Squeeze?

/ola

[Andreas Johansson]

What are you using to down convert? Avid? What container and what codec? Avid has lots to fix in the file export department.

[Jiri Bakala]

Since we are talking about downconverting and Avid, I have some relevant questions:

1. Would it be possible to capture SD from the EX1 directly into Avid with Mojo SDI while using the SDI output on the camera and its internal downconvertor?

2. And if so, can one control the 'deck' (the camera in this case) via the SD connection?

3. And last, would the signal from the SDI connector on the camera in the HD -> SD downconversion mode contain video, audio and TC as well?

[Ola Christoffersson]

Originally Posted by Andreas Johansson

What are you using to down convert? Avid? What container and what codec? Avid has lots to fix in the file export department.

I imported 1080i50-images in native format (HDV) into Avid MC. I then created a 50i-project and opened up the bin with the 1080i50-clips inside that project. The clips now play back fine in realtime in SD instead of HD which I find impressing. I assume this is a rough rescaling only though.
To get my final downconvert I used the Avid Transcode feature and transcoded the native HDV-material to uncompressed 10-bit SD. No losses in the final format that is.
But I still don't think it looks good. Is there a better way to do it?

[Ali Husain]

this might not help you, but sony vegas downconverts pretty well, and trivially easy without issues. you'll get 960x540 @4:4:4 color, and about half the noise. for SD this camera looks really really good.

[Ola Christoffersson]

Originally Posted by Ali Husain

this might not help you, but sony vegas downconverts pretty well, and trivially easy without issues. you'll get 960x540 @4:4:4 color, and about half the noise. for SD this camera looks really really good.

It's good to hear it is possible! I just expected the "world leader in editing" to have better transcoding. Still - my findings are very unscientific. I have tried a few clips and judged them with my eyes only.

[Per-Axel Gjores]

Originally Posted by Ola Christoffersson

I imported 1080i50-images in native format (HDV) into Avid MC. I then created a 50i-project and opened up the bin with the 1080i50-clips inside that project. The clips now play back fine in realtime in SD instead of HD which I find impressing. I assume this is a rough rescaling only though.

Do you mean that you create a standard definition project and open up the 1080i50 bin in that project, getting an instantaneous down convert to SD?

I haven't thought about that before, but now I've tested it and it really works! We have Avid Media Composers with Adrenaline hardware and DVCPRO25 decks connected via SDI to the Adrenaline. Running HD footage in an SD project enables our SD monitor, and it looks pretty good, I'm actually quite surprised! There is a slight interlace judder in the picture, but for basic SD conversion use, without the need to convert, transcode or render, it's really useful.

Actually you don't have to make an SD project first and then open up the HD bins. In the project bin you can just change the format of the project, from 1080i50 to 25iPAL!

This also enables us to make SD masters onto DVCPRO25 which can be useful.

Have you tried to make a DVCAM SD master yet?

Last night we made some SD conversions first converting into HDV and then using ffmpeg for the conversion to SD. I haven't looked closely at the quality. All I can say is that it took a lot of time, the timeline was 1½ hour long...

We will keep on trying finding other ways to down convert and if we find something out we will keep you posted!

/Ackel

[Ola Christoffersson]

Originally Posted by Per-Axel Gjores

Do you mean that you create a standard definition project and open up the 1080i50 bin in that project, getting an instantaneous down convert to SD?

I haven't thought about that before, but now I've tested it and it really works! //SNIPSNIP//
Have you tried to make a DVCAM SD master yet?


/Ackel

Yes I've tried outputting to DV. No problem. The workflow is actually very good going from 1080i to PALi. Thank's for the tip on changeing project format. Did not know you could do that.
What I am worried about is the quality though. I think I can see problems in the downconverted picture like I mentioned before. I´d like to know what is going on under the hood, so to speak. Is this downconversion optimal?
Have you tried downconverting using transcode? What do you thing about the picture quality?
Does anyone have some kind of resolution chart or something that can be used for testing this?

[Jiri Bakala]

Guys, what about my suggestion (as mentioned above)?

Use the camera to downconvert through its SDI out and take it into Avid via Mojo SDI?

Anyone?

[Per-Axel Gjores]

Originally Posted by Jiri Bakala

Since we are talking about downconverting and Avid, I have some relevant questions:

1. Would it be possible to capture SD from the EX1 directly into Avid with Mojo SDI while using the SDI output on the camera and its internal downconvertor?

2. And if so, can one control the 'deck' (the camera in this case) via the SD connection?

3. And last, would the signal from the SDI connector on the camera in the HD -> SD downconversion mode contain video, audio and TC as well?

Yes, it is possible to capture in standard def from the EX1's SDI output, video and embedded audio. We haven't tried it yet but it should work. The problem is you can't control the camera via SDI so you would have to 'crash' it into the Avid. And you will of course also loose the HD quality! I think most would like to be able to get two masters out of their EX1/Avid workflow, one HD and one SD. That's why down converting before inputting the footage is not the ideal way to go, at least that's how we feel.

/Ackel

[Ola Christoffersson]

Originally Posted by Per-Axel Gjores

Yes, it is possible to capture in standard def from the EX1's SDI output, video and embedded audio. We haven't tried it yet but it should work. The problem is you can't control the camera via SDI so you would have to 'crash' it into the Avid. And you will of course also loose the HD quality! I think most would like to be able to get two masters out of their EX1/Avid workflow, one HD and one SD. That's why down converting before inputting the footage is not the ideal way to go, at least that's how we feel.

/Ackel

Agreed! Also - it would feel horrible "recording" in real time from a $500-Sxs-card. That would make you loose all the benefits from solid state. Also - I don't own a Mojo... ;-)

[Jiri Bakala]

Originally Posted by Per-Axel Gjores

...And you will of course also loose the HD quality! I think most would like to be able to get two masters out of their EX1/Avid workflow, one HD and one SD. That's why down converting before inputting the footage is not the ideal way to go, at least that's how we feel.

Well, that's quite fine... because I am thinking about it in a little different way;

-shoot HD
-ingest from cards in HD into Avid/edit
-export final project in HD back to camera (card)
-capture again from the camera 'on the fly' in SD via SDI/Mojo SDI combo
-reorganize in Avid (TC, bars, other deliverables) and export to tape

Result: HD and SD masters of the same program.

Would this work?

[Ola Christoffersson]

Originally Posted by Jiri Bakala

Well, that's quite fine... because I am thinking about it in a little different way;

-shoot HD
-ingest from cards in HD into Avid/edit
-export final project in HD back to camera (card)
-capture again from the camera 'on the fly' in SD via SDI/Mojo SDI combo
-reorganize in Avid (TC, bars, other deliverables) and export to tape

Result: HD and SD masters of the same program.

Would this work?

To me this seems like a very complicated workflow. It would be much easier to just render to SD in the edit app. or other software. The only reason I can think of doing it that way would be if the cameras downconversion is superior to all software solutions, which i doubt.

[Per-Axel Gjores]

Originally Posted by Jiri Bakala

-export final project in HD back to camera (card)

Would this work?

At the moment I don't think any editing system is able to export back to the camera's card in native MP4 wrapped MPEG2 EX1 format. When this becomes possible your proposed SD mastering workflow would be feasible.

/Ackel

[Jiri Bakala]

Yes, I am aware that the NLEs are not yet capable of writing back to the card. I am trying to look ahead.

As for using the camera downconversion engine, yes, that proposed workflow is based on the presumption that hardware downconversion is better/faster or whatever else. If software path is better, great. In some situations it maybe a matter of time, though. Especially, if the program is long and the software conversion is slow.

I guess we'll see.... :-)