mpeg2 to vcd : input resolution does not affect output !!

[koorosh]

i am recording digital satellite programs using my dvb card from the following music channels :

----------------------------
viva polska :

average bitrate : 3745
resolution : 704*576
----------------------------
magic :

average bitrate : 1132
resolution : 352*288
-----------------------------

but when i encode the files to vcd format using TMPGEnc, the quality seems to be almost the same for output files !!

now my question is why do not input resolution and bitrate affect noticeably on output quality ?

[yoda313]

Hello,

If your destination is VCD the quality will be low because that's the nature of VCD. Unless you do a nonstandard XVCD.

Kevin

[OmegaSupreme]

The VCD standard calls for

PAL Video:
1150 kbit/sec MPEG-1
352 x 288 pixels
25 frames/second

NTSC/NTSC Film Video:
1150 kbit/sec MPEG-1
352 x 240 pixels
29,97 frames/second
23,976 frames/second NTSC Film

If your video is not in the specified format, it is converted during the VCD encode.

[koorosh]

Hello,

If your destination is VCD the quality will be low because that's the nature of VCD. Unless you do a nonstandard XVCD.

Kevin

thanks for reply

but quality is not low. it is very good.
i am wondering why the quality of the 704*576 input is not better ?

[babyboo]

Because regardless of the specifications of the input file (resolution, bitrate etc), if you are creating a standard VCD the output VCD files must all meet the same standards that OmegaSupreme mentioned above.

Edit...after re-reading your question a few times I think you might mean, and I am reading between the lines here...since the data rate and resolution of the original input file would normally be thought of as being of "better quality" than the other input file with lower bitrate and resolution...I would have to say perhaps the quality of the original source that the input file was created from was not the best...or perhaps the input file was created from a source where the bitrate was maxed out (in relation to the parameters of the source) and had gotten "all" that could be gotten (quality wise) out of the source. Basically it all comes down to the quality of the original source that your input files were created from. Personaly, a dba broadcast is a fairly decent source, however, I think that a bitrate of 3745 is kind of low for a resolution of 704x576 to begin with

[koorosh]

I think that a bitrate of 3745 is kind of low for a resolution of 704x576 to begin with

most of the digital channels have bitrate lower than 4000 with 720*576 aspect ratio which results in excellent video quality for broadcast.
i have made great vcds even from files with resolution 544*576 and bitrates lower than what mentioned above.

[lordsmurf]

The only time I've 4000k 720x576 video was from professional video servers from satellite companies. We typically cannot reproduce this as home.

I have 544x480 2000k VBR files that look okay, TIVO streams. Only with PROCODER in mastering settings can I come close to reproducing this.

You should look at SVCD. 480x480 should be fine.

[monzie]

Why cant you just use 1150kbs @ 352 X 288 (PAL VCD) to start with?

Downsizing a 704 X 576 means the footage has to be 'resampled' to turn a 2 X 2 pixel 'square' into a single (1 X 1) pixel....various resize filters are available (nearset neighbour, bilinear, bicubic, lanczos are the common ones) each employing a different method of re-sampling..which one did you use?...bilinear gives good results when downsizing.

And, if you have 2 VCD's of both the same bitrate what did you expect? DVD quality? You've just thrown away 75% of the resolution of the 704 X 576 REGARDLESS of the bitrate (which should really be around 4500kbs cbr to keep things equal...1150 X 4)....which your lower capture did in the first place............

As for bitrates these are a bit of a red herring as most people 'max' them out purely because they can due to the space available on a DVDr (and some people do 'yawn' 6 pass encodings 'yawn')....then happily use DVD Shrink/DVD-Rebuilder etc on a commercial DVD...............hmmmmm, I wonder what happens to the bitrate then?..........but saying that I still like to stay in the 'sweet' spot of 4500-5500kbs whenever possible.....but have used as low as 3400 with good results (6no tv sitcoms per dvd).

[koorosh]

You've just thrown away 75% of the resolution of the 704 X 576 REGARDLESS of the bitrate (which should really be around 4500kbs cbr to keep things equal...1150 X 4)....which your lower capture did in the first place............

thanks monzie

but i have not captured using a capture card , i have recorded the video clips using a dvb card which records digital broadcast without any quality loss.
the given resolutions and bitrates are satellite channel properties.they are broadcasting contents with these different resolutions and bitrates.
i expected the encoded clips to have at least some quality difference when converted to vcd ( 720*576 to have better quality when converted).
so my question is not answered yet.

[monzie]

But your question IS answered imo.

Why should the 720 X 576 (or 704 X 576) be ANY BETTER than the lower res when converted to VCD?

YOU ARE CONVERTING IT TO A LOWER RES/BITRATE.....why should it look better?

I cant understand your train of thought regarding this.

[SatStorm]

No, you need filtering. I do those things about 6 full years now. There was a time magic TV italy use to be 352 x 576 with a 2300 bitrate (and crappy picture, as still has...)
Viva Polska has good picture for now (expect a degration after 1/1/2005 - Viacom took charge of Viva Group, and that means crappy results - as happened already at Holland with TMF NL)
You can use both magic and viva as an "as is" source for DVDs (using TMPGenc author, just ignore the GOP limititation - if they pop up - and the bitrate limitation - it is fake).
In case you wish to re-encode to VCD then you MUST filter to have the best possible quality.
I suggest for this virtualdub mpeg 2, a modification of virtualdub capable to handle perfect ANY DVB source. Use Static Noise reduction ( 6 ) and Dynamic Noise Reduction ( 8 ) and frameserve to your encoder to re-encode to VCD.

Theory and practice are not always match you know. The perfect example, is Magic TV Italy. You see a DVB channel, and you don't know the background... Since it happens and I know it, let me post it here, just for the laugh of it...


First of all, for those who don't know, this is a local music station, outside Roma, with limited terrestrial broadcasting. It is among the few music station from Italy, not controlled by the "big ones"
We receive this channel in Europe, through Hotbird 3 satellite, at 13 East. But what we see, is a product of various previus convertions. Start counting:
1. Magic TV Italy sources are mostly VHS tapes (some bootlegs, taped from MCM Euromusique, early 90s...)
2. They link analogue from their studios, outside Roma, to the uplink station (about 12 km away). The uplink is a product of a realtime mpeg 2 convertion from analogue link. The uplink take places at the satelite NSS 7 at 22 West (SCPC form)
3. That feed is received at Slovenia (!) by RTV Slovenija, multiplexxed with other DVB channels (at this time 15 TV channels and 9 radio stations - all this in a 27 Mhz TP !!!!) and uplink again to Hotbird 3 at 13 East...

So, what you receive my friend is a VHS tape (or any analogue source), realtime converted to mpeg 2, uploaded to a satellite as an SCPC DVB channel, received by a company, remuxed with other channels (how that happens, I don't know. But I do know that the cheapest way is a digital reception to a DVB receiver- analogue transfer through S-video to the multiplexxor and a brand new digital convertion to a new TS stream for uplink), a second uplink to a commercial satellite (hotbird) and reception from your card...

Don't expect quality from something like this...

[koorosh]

But your question IS answered imo.

Why should the 720 X 576 (or 704 X 576) be ANY BETTER than the lower res when converted to VCD?

YOU ARE CONVERTING IT TO A LOWER RES/BITRATE.....why should it look better?

I cant understand your train of thought regarding this.

may be i am wrong, but i think 704 X 576 contains more picture details ( note that it's bitrate is about 3 times the other) and it will preserve more detials compared to the 352 X 288 when converted.

[ronnylov]

You are saying that your encoded VCD looks as good as your original source, despite the fact that the resoltion and bitrate of VCD is much lower, correct? It would be a similar case as if you encoded a DVD to VCD and you could not see any difference in the quality...

I do also have a DVB card, but dvb-c for cable TV and from my 704x576 sources of the better channels the quality is much better than an encoded VCD from the same source. Maybe your source did not contain much details (you can have high pixel resolution but still low details) or perhaps your TV is of low quality so the difference is hard to see.

Anyway, I don't see this as a problem, because that's what everybody wants - a result of your encoding that have the same quality as the original source!

EDIT: Ahaa, I missed that you are comparing the encoded result from two different channels and not compared one source with it's encoded version.
Well VCD cut outs all details above 352x288 no matter if the input resolution is higher and the channel with lower bitrate also had only 25 % resolution compared to the other so the bits/pixels was actually better for the magic source. That is why the end result would be about the same if you convert them both to VCD.

[koorosh]

Ahaa, I missed that you are comparing the encoded result from two different channels and not compared one source with it's encoded version.
Well VCD cut outs all details above 352x288 no matter if the input resolution is higher and the channel with lower bitrate also had only 25 % resolution compared to the other so the bits/pixels was actually better for the magic source. That is why the end result would be about the same if you convert them both to VCD.

thanks ronnylov
your description seems reasonable.
you say that bits/pixels value is the important parameter.

any other ideas ?

[junkmalle]

But your question IS answered imo.

Why should the 720 X 576 (or 704 X 576) be ANY BETTER than the lower res when converted to VCD?

YOU ARE CONVERTING IT TO A LOWER RES/BITRATE.....why should it look better?

I cant understand your train of thought regarding this.

may be i am wrong, but i think 704 X 576 contains more picture details ( note that it's bitrate is about 3 times the other) and it will preserve more detials compared to the 352 X 288 when converted.

Just think of it like this: the original video was probably full D1 (720x576). The version you get at 352x288 was reduced by the broadcaster and sent to you that way. The version you captured at 720x576 was sent to you that way and you converted it to 352x288. The only difference between the two VCD files is who did the conversion.

[lordsmurf]

I do not know of anybody sending signals at 352x288, so that conclusion is sort of ... off.

[koorosh]

Just think of it like this: the original video was probably full D1 (720x576). The version you get at 352x288 was reduced by the broadcaster and sent to you that way. The version you captured at 720x576 was sent to you that way and you converted it to 352x288. The only difference between the two VCD files is who did the conversion.

very good junkmalle

but there is something you have not taken into account.
dvb contents are transmitted in mpeg2 format.
so i have to encode the 352 X 288 file again to make a vcd.

[koorosh]

I do not know of anybody sending signals at 352x288, so that conclusion is sort of ... off.

this one is an example:

satellite : hotbird
channel name : magic tv
frequency : 12303
polarization : vertical
symbol rate : 27500

[junkmalle]

Just think of it like this: the original video was probably full D1 (720x576). The version you get at 352x288 was reduced by the broadcaster and sent to you that way. The version you captured at 720x576 was sent to you that way and you converted it to 352x288. The only difference between the two VCD files is who did the conversion.

very good junkmalle

but there is something you have not taken into account.
dvb contents are transmitted in mpeg2 format.
so i have to encode the 352 X 288 file again to make a vcd.

And your final files are VCD MPEG 1 -- a crappy format no matter what. There's no reason to expect either method to be significantly better than the other.

[ronnylov]

[quote="koorosh"]

thanks ronnylov
your description seems reasonable.
you say that bits/pixels value is the important parameter.

any other ideas ?

A lower resolution do not need the same bitrate as a higher resolution. I'm not sure the relation is linear (25 % resolution may require more than 25 % bitrate because the pixels are "zoomed" and encoding artifacts more visible).

I think 352x288 mpeg2 at 1132 kbit/s may have similar quality as 704*576 mpeg2 at 3745 kbit/s resized to 352x288 resolution, especially if you then reencode it to VCD quality. The encoder will resize your source before encoding to mpeg1 in VCD quality if it has another resolution. So I say Yes, bitrate and resolution of the source must both be concidered when judging the quality of the source. A higher resolution needs a higher bitrate to have the same relative quality.

But after encoding to VCD the quality differencies of the sources may be removed because VCD is a lower quality format and can not be better than the limits of the format.