DTT Video Files

Johnboy1951

Mods .... if there is a more suitable location for this, I could not locate it.

In this case I am recording video streams to a PC using a DVB dongle.

The video files recorded to PC from the Saorview signal are apparently either

544 x 576 25fps AVC 16:9 AR H.264/MPEG-4 AVC
or
1440 x 1080 25fps AVC 16:9 AR H.264/MPEG-4 AVC

with main audio a 2 channel MPEG Audio (Version 1) (Layer 2) --- mp2 --- at 192 kbps; what seems like a mono narration stream, along with Teletext/Subtitle

It seems obvious from the figures above that the video, as recorded, is not in 16:9 natively, which has me a little puzzled about what is done before and after transmission to get the best out of the video stream.

Can anyone explain or link to some explanation of how the video is to be treated?

To my way of thinking HD video in 16:9 would be
1920 x 1080 ... and not 1440 x 1080

and SD would be
1280 x 720

I am trying to reconcile my expectations of SD & HD to the information from the recorded streams.

regards.

Machinehead

AFIK BBC One HD & BBC HD use 1440x1080 for their freesat transmissions. (Lots of stuff on this on the DS forums re picture quality differences between BBC HD, ITV HD & Channel 4 HD). This mode of transmission requires less bandwith thereby allowing more channels per mux. I figure the same would apply to DTT, although RTÉ TWO may go to 1920x1080 when it moves to mux 2 allowing it more space.

fat-tony

There isn't a 1:1 correspondence between the transmitted pixel information and the pixels on your full HD display(TV) unless you're viewing full native 1920x1080 transmission. A couple of the ITV regions do display in this format (and also CH4 I think), but BBC and most ITV (and now RTE Two) use 1440x1080. This process is called anamorphic widescreen and reduces the horizontal resolution into fewer pixels which is then restored by the TV circuitry onto the full area of the screen - some parts of the picture are cropped or lost in the process due to the overscan of the TV.

Full SD resolution is 720x576 and only RTE Two used to broadcast in that format. RTE One and the others all use 544x576 and use the same anamorphic flag to indicate 16:9 material, which is then stretched back to the TV display size appropriately. Obviously using 544x576 instead of 720x576 loses picture resolution, but also saves on transmission bandwidth - which seems to be a more important criteria for our national broadcasting network provider:rolleyes:

Some German HD channels use 1280x720 transmissions in progressive format so there is a natural 16:9 ratio between them, but most full HD TVs have more pixels so it requires some re-scaling anyway.

Johnboy1951

EDIT: I am only speaking of Saorview .... I have no other reception over the air.

1440 x 1080 to display on a full HD screen will require black bars to fill the 1920.

BUT ...... has the video been scaled down (squeezed) into 1440, so that in transmission it is not to scale, on the assumption that it is to be scaled/stretched to 1920 on receipt?

I guess the question is ...... is 1440 x 1080 the correct AR to display the transmitted signal, without any distortion, or is there 'distortion' built in that can be corrected by displaying at 1920 x 1080?

regards

fat-tony

Johnboy1951 wrote: »

EDIT: I am only speaking of Saorview .... I have no other reception over the air.

OK - let's stick to Saorview!

1440 x 1080 to display on a full HD screen will require black bars to fill the 1920.

No - it's stretched to the 16:9 display ratio. Commercial movies which have a higher ratio will have black bars inserted by the TV playout system usually.

BUT ...... has the video been scaled down (squeezed) into 1440, so that in transmission it is not to scale, on the assumption that it is to be scaled/stretched to 1920 on receipt?

Yes - it's "squeezed" by the anamorphic process at transmission to fit and "unsqueezed" by the TV to fit back into 1920x1080. If the TV is not full HD it will still "unsqueeze" it to the correct ratio, but obviously has fewer pixels to play with, so will lose resolution. If you display the 1440x1080 on a PC (say) in 4:3 ratio the picture appears squeezed.

I guess the question is ...... is 1440 x 1080 the correct AR to display the transmitted signal, without any distortion, or is there 'distortion' built in that can be corrected by displaying at 1920 x 1080?

The aspect ratio is not 1440x1080 (it's set as either 4:3 or 16:9 in the transmission data). It's just a container for the picture information.

I've tried to answer your queries without getting into too much tech speak. Several of us on this forum have issues with the sacrifice of video and audio quality in Saorview transmissions because the services have been squashed into one multiplex. We hope that when a second multiplex is used, some of the existing services will be improved in resolution and use lower levels of compression.

Johnboy1951

Thanks for the info

So as I understand it, the HD transmission should be scaled from 1440 x 1080 to 1920 x 1080 in order to display the original content correctly.


Presumably something similar is done with the SD transmissions ...... which can be scaled to 1920 x 1080 (?) also displaying the original content correctly?


Thanks again.

fat-tony

There's no difference in aspect ratio handling between SD and HD. It's just the pixel count which is higher in the HD transmissions which makes for the higher resolution possibility. There are lots of TVs which won't have 1920 x 1080 pixels but still display a very acceptable picture quality in the correct aspect ratio. I have a 37" Panasonic which I bought years ago which is 1360 (and something) by 768 and has a smashing picture both on SD and HD transmissions. I'd say it's the equal of my other set (which is full HD) at normal viewing distance. Don't forget that most TVs overscan, so you are losing some information from all around the borders of the picture anyway. My full HD set can turn off the overscan to display the exact picture information from the source. In this mode, one of my terrestrial tuner boxes will not display a full picture on the screen, but the other will.
The other side of the coin is that RTE Two are transmitting everything at the moment with the widescreen flag set on. Have a look at cartoons (The Simpsons) which are natively in 4:3. This is stretched by the TV to fill the screen, but technically should have black bars at each side and be displayed as a 4:3 image. They will fix this once their HD playout system is in place, I guess. Some people don't like 4:3 material displayed with black bars at the side and will set their TVs to "stretchyvision" to eliminate them. I have a preference for material to be displayed in the correct aspect ratio.

Johnboy1951

Should not be done I guess but I am posting again ....

Here is a pic of a SD video being played on my PC ..... an excerpt I recorded from TG4 last weekend.

The full screen pic shows black bars all around.

This implies to me ..... and am of course open to correction .... that some black has been included in the transmitted video, and VLC (in this case) is maintaining the aspect ratio by automatically adding black bars to the other two sides.

If there were no blak bars in the original, then VLC on Full Screen setting would be expected to scale the video to the max while maintaining the pic at 16:9

Your comments on this would be appreciated.

Thank you.

Pic available here to show what I mean. The display's resolution in this case in 1680 x 1050

fat-tony

I saw your post on the other thread, so I can see what technical details you posted there. I would assume that this is a movie rather than a TV production, so the aspect ratio would be greater than 16:9, which would result in black bars at the top and bottom being inserted for the TV release (or the DVD release for that matter). The side bars are some artefact of how you are playing it in VLC player. I can display any recording from Saorview in DVBViewer Pro or in VLC Player or in Media Player Classic in full screen and there are no bars at the side of any widescreen programme. There may be bars at the top and bottom, but not on the side also. Any chance of posting part of the recorded file on some file-sharing site?

Johnboy1951

If I can get a short bit uploaded I will post a link in this post ..... my upload speed is almost non-existant so it might take some time

Thanks for taking an interest

regards.

EDIT:
Here is a link to a 16sec clip of the film. The video stream is untouched but the nar and teletext streams are omitted ..... they were dropped when I 'corrected' the wrapper format from Kaffeine so VLC could play it.

It does not seem to matter which player I use I still get the same 4 black bars .... and they are there on the original recording as well as any clips I have 'played' with since.

fat-tony

Of all the movies, in all the world, you had to pick this one:eek:

Seriously though, from looking at a couple of excerpts and trailers on youtube etc. it looks like this movie was letterboxed into a 4:3 TV frame at some stage and now when it is shown on 16:9 TV it appears that you are looking through a window frame at the movie as it is pillarboxed as well as letterboxed.
Some of the cheapo movie channels on satellite often show cheapo movie prints at either the wrong aspect ratio or with dreadful sound or in this windowboxed format. I suspect this particular movie suffered a poor transfer to video tape or to DVD or whatever at some time and this is the copy that TG4 had.

Now if ALL your recordings from TG4 or RTE One or whatever, look like this, then that is a different matter. Note that TV3 and 3E often show 4:3 material with the 16:9 flag set so everything is stretched out.

Johnboy1951

Thank you for looking at this.
As this was the only thing I had recorded ..... just began trying out a few things ..... like getting the wee remote working and recording and such .... I never gave much thought to other films .

Thanks for the explanation of what might have caused this to be so.

regards

Johnboy1951

To finalise this thread ...... as I understand the situation, some of the content being broadcast has those black bars in the original content and thus they are displayed as part of the film.
In the case of the film I mentioned above those bars are on all four sides.
I did notice - again on TG4 - while playing about, that the series Bonanza also seems to be 'windowed'.

All other content I have viewed is as expected.

***

I am becoming more enamoured with this means of recording Saorview content due to the reports of encryption being applied to the recordings in some (what percentage I do not know) PVR STBs.
I suppose until there are many official Saorview certified boxes on sale the percentage will not become clear.

I would be rather upset to find I could only view a PVR recording from the STB that recorded it and nothing else ......

regards.

Apogee

Johnboy1951 wrote: »

I am becoming more enamoured with this means of recording Saorview content due to the reports of encryption being applied to the recordings in some (what percentage I do not know) PVR STBs.

I don't recall RTÉ/RTÉNL making any mention of encrypting Saorview content on PVRs thus far.

The problem we've seen reported is with the use of UK Freeview HD equipment, not Saorview certified boxes.

Johnboy1951

Apogee wrote: »

I don't recall RTÉ/RTÉNL making any mention of encrypting Saorview content on PVRs thus far.

The problem we've seen reported is with the use of UK Freeview HD equipment, not Saorview certified boxes.

It is good to know that RTE are not making a demand for it ...... but of course the manufacturers of the STBs may still include it I suppose .....

It is something that will be a deciding factor for me when it comes to buying a PVR STB or not ....... should I decide to go down that route.

regards.

Apogee

Johnboy1951 wrote: »

It is good to know that RTE are not making a demand for it ...... but of course the manufacturers of the STBs may still include it I suppose .....

Manufacturers of STBs don't care - they only want to sell more STBs. If the ability to transfer material from their STB to USB means higher sales, fine by them.

The pressure comes from programme copyright holders. They have a vested interest in making the copying of HD material as difficult as possible.

fat-tony

Johnboy1951 wrote: »

To finalise this thread ...... as I understand the situation, some of the content being broadcast has those black bars in the original content and thus they are displayed as part of the film.
In the case of the film I mentioned above those bars are on all four sides.
I did notice - again on TG4 - while playing about, that the series Bonanza also seems to be 'windowed'.

All other content I have viewed is as expected.

***

I am becoming more enamoured with this means of recording Saorview content due to the reports of encryption being applied to the recordings in some (what percentage I do not know) PVR STBs.
I suppose until there are many official Saorview certified boxes on sale the percentage will not become clear.

I would be rather upset to find I could only view a PVR recording from the STB that recorded it and nothing else ......

regards.

Bonanza is a TV series shot in 4:3 aspect ratio and should be "pillarboxed" on a 16:9 TV - black bars each side. I haven't noticed any "letterbox" bars particularly, but I'll keep an eye out for when it's next on:)

As Apogee said - don't worry particularly about encryption of video files on boxes. The manufacturers only put that on Freeview and Freesat boxes because they had to as part of the licence terms. It is, though, a point to be aware of if you are contemplating buying a branded Freeview HD recorder and you want the facility of playing the recordings on other platforms without extra hassle.

Johnboy1951

fat-tony wrote: »

Bonanza is a TV series shot in 4:3 aspect ratio and should be "pillarboxed" on a 16:9 TV - black bars each side. I haven't noticed any "letterbox" bars particularly, but I'll keep an eye out for when it's next on:)

As Apogee said - don't worry particularly about encryption of video files on boxes. The manufacturers only put that on Freeview and Freesat boxes because they had to as part of the licence terms. It is, though, a point to be aware of if you are contemplating buying a branded Freeview HD recorder and you want the facility of playing the recordings on other platforms without extra hassle.

Please do let me know if you see the same behaviour on some of those old TV series ..... I would like to be certain it is not some setting here that is causing it. Thanks

I have also had an interesting time multicasting the mux over the LAN and being able to play any TV channel on any PC connected to the LAN ..... fun times

regards