Reencoding HDTV 1080i to DVD Mpeg2

[bedlam]

Hi all, this my first post....be nice with me.

I have a 1080i ts Video file which I want to convert to DVD, the video file is 2.5GB 38min long.

Now here is the bit I'm confused with....

The ts video is 1920x1080 resolution and 2.5GB in file size.
When I convert the video to DVD which is 720x576 resolution (more than half the resolution of the HDTV file), why is the resulting DVD mpeg video file the same size ???? I would of thought since the DVD is half the resolution of the HDTV file, then it would be half the file size ????

Can anyone xplain this ?????

[ChrissyBoy]

Resolution has nothing to do with it. it is the video bitrate which is important. What is the bitrate of the ts file? i suspect it is the same as the bitrate for the mpeg2 file.

[Baldrick]

What do you convert with?

If you want to lower the output size you just change the video bitrate and it has nothing to do with the video resolution.

[Cornucopia]

38 min. * 60 sec./min. = 2280

Very high quality DVD MPEG2 ~= 8500kbps

8500kbps * 2280 = 19380000 kb or 2.365GB

It'll be more when you add in the audio, but that's close. That's your target.

Why worry about what the source bitrate or size was, as long as: you could fit it onto your hard drive to begin with, and it was good enough quality to watch enjoyably?

Don't need to think about anything else.

Scott

[bedlam]

The HDTV ts video is 29.97fps 80000kb/s according to DivXToDvd.
The Reencoded DVD mpg file is 29.97fps 7800kb/s.

It just doesn't add up to me ????

I thought the bit rate is related to the image resolution, larger image resolution = more bits to process.

It still doesn't explain why the reencoded dvd mpg file which is less than half the resolution and 10 times less the bitrate, but it is still the same size video file as the HDTV video ???????

The quality of the HDTV video is very impressive but the reencoded DVD mpg is not as good (just your avergae dvd quality).

But why the video file sizes the same ???

[Baldrick]

Resolution has nothing to do with the bitrate.

DivXtoDVD just uses the highest possible bitrate so it will fit on a DVD. If you change/lower the output size in divxtodvd the video bitrate will be lower.

[bedlam]

38 min. * 60 sec./min. = 2280

Very high quality DVD MPEG2 ~= 8500kbps

8500kbps * 2280 = 19380000 kb or 2.365GB

Well if I use your equation for the HDTV video, it should be 18.92GB and not 2.5GB:

38 min. * 60 sec./min. = 2280

HDTV ts video ~= 80000kbps

80000kbps * 2280 = 182400000kb or 18.92GB


Why is the HDTV video which is 80000kbps only 2.5GB in size ?????

[bedlam]

Resolution has nothing to do with the bitrate.

DivXtoDVD just uses the highest possible bitrate so it will fit on a DVD. If you change/lower the output size in divxtodvd the video bitrate will be lower.

Your reply doesn't make sense, you say the bitrate has nothing to do with the resolution of the image/video, but then you say if I change/lower the output size (say 352x576) of the image/video then the bitrate wil be lower.

this suggests the resolution does have somthing to do with the bitrate.

[borax]

80000kb/s

I think this is just a garbage value (something like the 15000 kBit that is used for dvb in nearly all german dvb channels - the actual max. rate is rarely higher than 6000 kBit). The actual (average!) bitrate of your HDTV can't be anything other than 9600 kBit (as the 'total' bits are 21978152960, total time in sek is 2280, the quotient is 9639540 bits/sec!!!). The bitrates are completly independent from the resolution. It would be possible to have a resolution of 4000x3000 with a bitrate of 100 kBit (although you would probably not recognize a 'picture')...

[Cornucopia]

Bitrate is only related to image resolution if you're talking about UNCOMPRESSED video (e.g.: 720 x 480 x 24bit x 30fps).

Since 90% of what we're talking about is DV or MPEG related (both compressed), you must divest yourself of these quaint notions.

Each resolution, using a particular codec scheme, has a certain QUALITY associated with it that roughly corresponds with bitrate. This is also "Scene Complexity" dependant.

Therefore:

NTSC 720x480, DV codec = 25Mbps (only)
NTSC 704or720x480, MPEG2 (DVD constrained) codec = 1-9.8Mbps, with quality being acceptable usually around the 3.5Mbps mark and above, and being excellent usually around the 7.5Mbps mark and above.
NTSC 352x480, MPEG2 (DVD constrained) codec = 1-9.8Mbps, with quality being acceptable usually around the 2Mbps mark and above, and being excellent (for such reduced resolution) usually around the 4Mbps mark and above, and being a waste of bitrate/space if used for >5.5Mbps (because of no visible improvement in the "transparency" of the codec).
NTSC 352x240, MPEG1 (DVD constrained) codec = ~1-2Mbps, with quality being acceptable at VCD rates (1150kbps) and being excellent (for it's much-reduced resolution) at 1.8Mbps and above.

HD has similar ranges ((EDIT: "with bitrates extended in the upper limit to accommodate quality required with such increase in resolution")), but with obviously much greater compression efficiencies if using MPEG4 codecs (particularly H.264) or WMV codecs.

<<I think that's what was confusing you.


Scott

[DVWannaB]

bedlam,

There is something wrong or should I say odd about the bitrate of your HiDef file. If the source of you video was TRUE HiDef the bitrate would be around 20 Mbps or higher. For me I get about 1 hour ~ 8GB file size. So for 38 minutes you should be around 5GB. My guess is that you probably recorded an upscaled video source from 720x480 up to 1920x1080, but in so doing, they did not bump up the video bitrate to match a true HD broadcast. 8 Mpbs is not true HD bitrate. 8 Mbps sounds like a doubling of a satellite TV regular movie channel bitrate, which is around 3.5 to 4 Mbps (like HBO, Showtime, etc). Could be an explanation for your small file size. Unless they source video is using MPEG4 compression algorithm, which I hear are starting to roll out now. MPEG4 requires a lower bitrate to achieve similar PQ.

[Cornucopia]

Could be nothing wrong with the file or filesize if it happened to be encoded as MPEG4, etc. (Or if the scene/content is so simple and unmoving)

Scott

[bedlam]

HD has similar ranges, but with obviously much greater compression efficiencies if using MPEG4 codecs (particularly H.264) or WMV codecs.

<<I think that's what was confusing you.

Ahh, I think I begin to understand now, so it's the actual compression scheme (encoder) that determines the size/quality of the video ??

So DVD is mpeg2 based which is not as good as HDTV mpeg4 encoders ???

[Cornucopia]

(Somewhat) Yes

and

Yes.

Scott

[bedlam]

bedlam,
There is something wrong or should I say odd about the bitrate of your HiDef file.

The bitrate 80000kbps is shown as Maximum [VBR]. The quality is very impressive (twice as good as DVD) so I guess it is true 1920x1080 HDTV video. It was recodred from INHD2 cable channel.

[bedlam]

(Somewhat) Yes

and

Yes.

Scott

Gooood....

So if I were reencoding to DVD standard size/bitrate using Mpeg4 encoder instead of Mpeg2 then I would probably expect the size to be much smaller......it makes sense now....thanks all.

[DVWannaB]

bedlam,
There is something wrong or should I say odd about the bitrate of your HiDef file.

The bitrate 80000kbps is shown as Maximum [VBR]. The quality is very impressive (twice as good as DVD) so I guess it is true 1920x1080 HDTV video. It was recodred from INHD2 cable channel.

I forgot to mention in my post, but some HD subscription services are starting to use MPEG4 compression codec in their HD broadcasts, which uses a lower bitrate to achieve simialr picture quality. this may be the reason for your small file size, great picture and HD resolution (1920x1080). I know Verizon FIOS TV has done this is small pockets throughout the US and I believe DirectTV is starting to do the same.

[DVWannaB]

So if I were reencoding to DVD standard size/bitrate using Mpeg4 encoder instead of Mpeg2 then I would probably expect the size to be much smaller......it makes sense now....thanks all.

Hmmmm, not quite (I think). See I can make sense of this. DVD uses MPEG2 (not MPEG4). So you cant relate DVD and MPEG4. They are different standards, as far as compliancy is concerned. The only thing that makes them similar is bitrates, resolutions, etc. In that 5Mbps will yield a similar file size whether it is an MPEG2 (DVD) or MPEG4 file. So MPEG4 is not a DVD standard.

So to convert your HD file to play in your DVD player, I would say use the same bitrate (8000) and just lower resolution to 720x480.

[Cornucopia]

(Somewhat) Yes

and

Yes.

Scott

Gooood....

So if I were reencoding to DVD standard size/bitrate using Mpeg4 encoder instead of Mpeg2 then I would probably expect the size to be much smaller......it makes sense now....thanks all.

Yes, except LOSE the "size/bitrate" part. Say "resolution & quality" and you will be targeting a range of bitrates with MPEG4 that is somewhere between 1.25-4x more efficient than MPEG2 (depending on content again).

Remember, in EVERY corner of the video and audio world--

• BITRATE * TIME = FILESIZE

(and of course, if you want DVD compatibility, you can't use MPEG4, only MPEG2 or MPEG1--constrained to DVD parameters)

Scott

[Cornucopia]

Remember, in EVERY corner of the video and audio world--

• BITRATE * TIME = FILESIZE

(and of course, if you want DVD compatibility, you can't use MPEG4, only MPEG2 or MPEG1--constrained to DVD parameters)

Scott

Notice there is no mention of RESOLUTION or QUALITY...

Scott

[bedlam]

So if I were reencoding to DVD standard size/bitrate using Mpeg4 encoder instead of Mpeg2 then I would probably expect the size to be much smaller......it makes sense now....thanks all.

Hmmmm, not quite (I think). See I can make sense of this. DVD uses MPEG2 (not MPEG4). So you cant relate DVD and MPEG4. They are different standards, as far as compliancy is concerned. The only thing that makes them similar is bitrates, resolutions, etc. In that 5Mbps will yield a similar file size whether it is an MPEG2 (DVD) or MPEG4 file. So MPEG4 is not a DVD standard.

So to convert your HD file to play in your DVD player, I would say use the same bitrate (8000) and just lower resolution to 720x480.

I was just using that as an example, I have already sucessfully converted the file to DVD and I'm happy with (obviously the quality is not as good as the HDTV because it's half the resolution).

Guess what........I'm confused again

Just checked the HDTV ts video file in TmpGenc and it's a Mpeg2 video file not Mpeg4 ?????

So given that the HDTV 2.5GB video file is Mpeg2 with higher resolution/bitrate than the lower resolution/birate DVD Mpeg2 video file which is still the same size +- a few MB ????

I'M CONFUSED AGAIN....sorry

[bedlam]

OK...here is some more details:

I did 2 conversions of the HDTV video file:

1. Using DivxToDvd gave me a 770MB 9100kbps VBR DVD Vob File.

2. Using HDTV2DVD gave me a 2.5GB 7800kbps VBR Mpeg2 File.

It seems the HDTV2DVD conversion has gone wrong somewhere as the file size doesn't make sense here ??

The HDTV2DVD conversion looks better quality than the Divx2Dvd conversion but only a very small difference. Not enough to justify almost an extra 2GB of data.

So it must be the HDTV2DVD program which is giving me badly sized video files. It's much slower a converting than DivxToDvd too.

Stupid program, I been scrathing my head over this and it's all down to HDTV2DVD giving wrong info.

Anyone else here had similar experience of this ?????

[borax]

1. Using DivxToDvd gave me a 770MB 9100kbps VBR DVD Vob File.
2. Using HDTV2DVD gave me a 2.5GB 7800kbps VBR Mpeg2 File.

Again: Do not believe these kbps values! Once more:
BITRATE * TIME = FILESIZE

IIRC HDTV2DVD can be used as demultiplexer only too. In this case it will not change the resolution, just remove the broadcast info and split the movie in one video and one audio stream. You may then reencode the video stream with CCE, TMPGEnc, HC... with the best possible settings (to keep as much quality on the final dvd as possible) and author the elementary streams with a dvd authoring program.
But if you are content with the output of divx2dvd with an average bitrate of only 2800 kbps, the original quality can't be that good...

[Cornucopia]

what borax means is that given the "bitrate * time = filesize" equation, that means:

• FILESIZE / TIME = BITRATE (average, not peak/max)

So you have 770 (*8bit/1Byte) / 2280 = 2.7Mbps!
Not very good quality at all for 720x480 rez. (Remember my ranges above..)

It may say 9100kbps VBR, but that is its peak, not average, value.

Scott

[edDV]

bedlam,

... 8 Mbps sounds like a doubling of a satellite TV regular movie channel bitrate, which is around 3.5 to 4 Mbps (like HBO, Showtime, etc). Could be an explanation for your small file size. Unless they source video is using MPEG4 compression algorithm, which I hear are starting to roll out now. MPEG4 requires a lower bitrate to achieve similar PQ.

Interesting, are satellite "premium" channels only 3.5-4.0 Mbps MPeg2 ?

Here is what Comcast is feeding on a new 750MHz rebuild. (all MPeg2 TS streams)

InHD - 25Mbps 1080i
HBO HD - 20Mbps 1080i
ESPN HD - 25Mbps 720p
HD Locals - 20-25 Mbps 1080i or 720p

HBO SD etc. - 15 Mbps 528x480

Typical "digital" channels 8-15 Mbps 528x480

DirecTV is converting HD to MPeg4. Broadcasters factor MPeg4 to about half MPeg2 (13-19 Mbps for HDTV). So that would put MPeg4 1080i around 6.5-9.5 Mbps range.

It will be interesting to see what DirecTV actually feeds for HD.

[ChrissyBoy]

2. Using HDTV2DVD gave me a 2.5GB 7800kbps VBR Mpeg2 File.

...

Stupid program, I been scrathing my head over this and it's all down to HDTV2DVD giving wrong info.

WRONG. So wrong...:


Your source is 38min duration. 38 mins is 2280 secs. As you state HDTV2DVD used 7800Kbps which results in 17784000 kbits. Which is 2223000 KBytes, which is 2.12 GB. Add your audio and you have your 2.5GB....

This is what you would expect from any source of 38 mins duration encoded at 7800kbs.

Nothing wrong with HDTV2DVD: it is being ask to encode 38 mins @ 7800kbs... yet YOU have a problem with 2.5GB as a result

[bedlam]

WRONG. So wrong...:

Your source is 38min duration. 38 mins is 2280 secs. As you state HDTV2DVD used 7800Kbps which results in 17784000 kbits. Which is 2223000 KBytes, which is 2.12 GB. Add your audio and you have your 2.5GB....

This is what you would expect from any source of 38 mins duration encoded at 7800kbs.

Ok, then explain why the HDTV video file which is 80000kbs, twice the resolution and quality but also 2.5GB in size...it just doesn't add up.

If I'm reencoding to a lower bitrate and resolution and also losing some quality in the process, explain why the video file is still 2.5GB ?????

There is not much difference in quality with the 770MB and 2.5GB encodes. Certainly not 2GB of extra video data difference.

I'm no mathemation but I do know that if you take a bag of marbles and take away half of them, you are left with half and not the same full bag......so to speak.

What is the average bitrate of a good quality 1920x1080i HDTV mpeg2 video ????

What file size could I expect if it were 38mins long ????

[bedlam]

I just been reading some of the articles and it looks like the only explaination could be that the HDTV ts video file that I have is encoded
as 8Mbps and not 18 or 19Mbps as you would expect for a broadcast HDTV video.

This explains why the size of the video file is no different when re-encoded to DVD.

Does that make sense ???

Just say yes if you are growing tired of this discussion

[DVWannaB]

I just been reading some of the articles and it looks like the only explaination could be that the HDTV ts video file that I have is encoded
as 8Mbps and not 18 or 19Mbps as you would expect for a broadcast HDTV video.

This explains why the size of the video file is no different when re-encoded to DVD.

Does that make sense ???

Just say yes if you are growing tired of this discussion

I guess you just totally blew off my post above I think thats what I at least attempted to say. What you should do is ask you HD provider if they are broadcasting HD content with MPEG4 or MPEG2. Like I said earlier MPEG2 *.ts stream is around 19-25 Mbps. MPEG4 *.ts stream will be much lower at around 8-12 Mbps or even lower. If they are using MPEG4 this ends this discussion.

Also HDTV2DVD converts your *.ts stream to DVD MPEG2 (not MPEG4). DVD is MPEG2. HD resolution above 720x480 is not DVD compatible, so that is why when you convert your file it shrinks from 1920x1080 to 720x480. Therefore, although bitrate is the same in converted file as original HD file, it does not look as good.

Do some more reading on MPEG2 and MPEG4. Generally speaking MPEG4 uses a lower bitrate to achieve the same PQ as MPEG2. So your 8 Mbps HD file, if it is MPEG4, is the equivalent to a 20 Mbps HD MPEG2 file. Only thing, is that the file size is more than doubled. Therefore, MPEG4 is more efficient at compressing video than MPEG2.

[bedlam]

Yep, you're right. The HDTV stream is 9.1Mbs. you and ChrissyBoy did mention it but I been thinking it was much higher than that and getting confused with picture image resolution/bit depth like you said.

Well, I guess this ends the topic...thanks all for the replies.

If only customer support forum's were like this and you guys do it for free....great stuff.