MPEG Question regarding specs (Bitrate, Ratio, Resolution)

[hcowan]

Hello,

I have a bunch of questions that I am hoping to get sorted out. I have a JVC MiniDV Camcorder which I have used to shoot lots of home video. I wanted to e-mail some of the clips to people so I dumped the DV video from tape to my DVD-recorder (which has a DV input) and recorded it onto DVD+R. I set the quality to the highest so I get just over an 1 hr per disc.

I used the tool "MPEG Stream Clip" to isolate (trim / cut) specific clips for e-mailing. When I opened the initial DVD (VOBs) in StreamClip and looked at the stream info option I get:

Video Track:
720x480
4:3
10.00 Mbps

My Camcorder has the option to record in 16:9 which I used. How come it states then that the ratio is 4:3 and NOT 16:9. In addition, when I view the clip using VLC it looks squished, but when I view it on the Camcorder it isn't.

Also, does anyone know what the resolution would be 16:9 widescreen? I understand the 480 as that is the scan lines, but if that is the case, should the vertical be 854? (480 x 1.7778)

Finally, when I used "MPEG Stream Clip" to save the trimmed video, and then re-open that file, my Bitrate goes from 10 Mbps down to 8 Mbps. I was under the impression that "MPEG Stream Clip" allowed you to edit video without re-encoding.

If that's true, why did my bitrate change?

Thanks so much.

Hugh

[PuzZLeR]

Can we get you to post a small sample, or at least give us a text readout from MediaInfo? It would help. But we can try.

Video Track:
720x480
4:3
10.00 Mbps

Assuming it's just the video portion that is 10mbps, it's not DvD compliant past 9.8mbps.

My Camcorder has the option to record in 16:9 which I used. How come it states then that the ratio is 4:3 and NOT 16:9. In addition, when I view the clip using VLC it looks squished, but when I view it on the Camcorder it isn't.

A sample here would help. Maybe your settings, or your camera, aren't doing it right. As well, do you see any black banding anywhere?

Wondering as well, are you confusing DV video with MPEG-2 somewhere? Both may have a different Pixel Aspect Ratio (PAR) and causing disortion.

Also, does anyone know what the resolution would be 16:9 widescreen?

Both, 720x480 and 720x576, the full DvD resolutions for NTSC and PAL respectively, support, both, 4:3 and 16:9.

I understand the 480 as that is the scan lines, but if that is the case, should the vertical be 854? (480 x 1.7778)

You assumed square pixels in the Pixel Aspect Ratio (PAR =1:1), which is not the case for DvD video, and you're confusing it with Display Aspect Ratio (DAR), which can be either 4:3, or 16:9, for DvD.

Your mathematics would work with these values:

720x480 (NTSC)
DAR = 4:3 -> PAR = 8:9
DAR = 16:9 -> PAR = 32:27

720x576 (PAL)
DAR = 4:3 -> PAR = 16:15
DAR = 16:9 -> PAR = 64:45

Using the following equation, and some algebra, will always steer you correct :

Width / Height = DAR / PAR

Finally, when I used "MPEG Stream Clip" to save the trimmed video, and then re-open that file, my Bitrate goes from 10 Mbps down to 8 Mbps. I was under the impression that "MPEG Stream Clip" allowed you to edit video without re-encoding.

If that's true, why did my bitrate change?

I can't say for sure since I don't have a sample stream, and don't use MPEG Stream Clip, but maybe it's only just changing some header, not re-encoding the video, that "changes" the bitrate flag.

Maybe your MPEG-2 video is indeed compliant at its "true" bitrate of 8mbps instead of the initial reading at 10mbps, which MPEG Stream Clip may be correcting.

Personally, whenever I capture any MPEG, via camera, TV, VHS, etc, I always run it through VideoReDo using QuickStream Fix. This corrects the GOPs, timing errors, heading errors, and more, usually associated with captured MPEG video that is encoded on the fly.

[jagabo]

It sounds like your DVD recorder marked the video as 4:3 instead of 16:9.

Regarding bitrates: use a reliable program like GSpot or Bitrate Viewer. Those actually read through the entire file and report the bitrate. Most other programs just look at the header which may no reflect the true bitrate.

[poisondeathray]

You could use dvd patcher or restream to "fix" the AR

[hcowan]

Hi,

Thanks so much for your reply and detailed information. Sorry it took me so long to respond, but I have never heard of PAR / SAR / DAR so I wanted to gather some more information before posting so I don't appear too stupid.........

Can we get you to post a small sample, or at least give us a text readout from MediaInfo? It would help. But we can try.

These are screen shots taken from the converted DVD source. I can post a small clip if you still need it.

The first screen below shows what "MPEG StreamClip" shows:



As you can see, "MPEG StreamClip" reports the bitrate as 10.00 Mbps for the video field, 720 x 480 for the resolution, and 4:3 as the ratio.


"MediaInfo" reports the following.................


General

Complete name : D:\VIDEO_TS\VTS_01_1.VOB
Format : MPEG-PS
File size : 435 MiB
Duration : 7mn 12s
Overall bit rate : 8 422 Kbps


Video

ID : 224 (0xE0)
Format : MPEG Video
Format version : Version 2
Format profile : Main@Main
Format settings, BVOP : Yes F
ormat settings, Matrix : Default
Format settings, GOP : M=3, N=15
Duration : 7mn 12s
Bit rate mode : Variable
Bit rate : 7 999 Kbps
Nominal bit rate : 10 000 Kbps
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 4:3
Frame rate : 29.970 fps
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.772
Stream size : 413 MiB (95%)

It reports the "nominal" bitrate as 10,000 Kbps but the bitrate as 7,999 Kbps. I had set the DVD recorder quality to high which gives 1 hour and 12 minutes recording time per disc.

If a DVD+R is 4.7 GBs (4,812 MBs), 72 minutes (4,320 seconds) of recording time would give an average rate of 8.92 Mbps if my calculation is correct, which doesn't match either value?

When I use the "Bitrate Viewer" application I get the following:




And finally, "GSpot" reports:




Which you will notice shows the resolution as 720 x 480, but indicates that the DAR is still 1.33 or 4:3 (ie: not widescreen).

I finally understand the difference between PAR, SAR, and DAR, and can make the calculations work out properly. But I am still confused as to why the original DV recording is 720 x 480 widescreen (16:9) and the DVD recording is also 720 x 480 but fullscreen (4:3).

To try and figure it out I did a direct MiniDV to Computer transfer via firewire and got the following screen from "GSpot":



Which you will notice has the same resolution of 720 x 480, but has a DAR of 16:9 or Widescreen. I am not sure why then when converted to Mpeg2 it wouldn't keep the same DAR.

I would assume that as the storage resolution or SAR is the same, the actual pixel information does not change (other than being recompressed), so shouldn't the PAR remain the same?

Is the PAR fixed for a specific format (ie: MPEG, DV) or can it be variable / different?

Is the PAR stored within the actual file / header, or is it just calculated based on other factors (ie: resolution and display ratio)?

Funny, when I run "MediaInfo" for the MiniDV file, it reports the ratio as 3:2 which is the same as the SAR, which it seems would assume a PAR of 1:1.

General

Complete name : C:\test.avi
Format : AVI
Format/Info : Audio Video Interleave
Format_Commercial_IfAny : DV
File size : 127 MiB
Duration : 35s 869ms
Overall bit rate : 29.7 Mbps

Video

ID : 0
Format : DV
Codec ID : dvsd
Codec ID/Hint : Sony
Duration : 35s 869ms
Bit rate : 28.5 Mbps
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 3:2
Frame rate : 29.970 fps
Standard : NTSC
Color space : YUV
Compression mode :
Lossy Bits/(Pixel*Frame) : 2.747
Stream size : 122 MiB (96%)

So I understand a bit more than I did, but I am still somewhat confused. I don't know if any of this information helps or not.

In the specific case of MPEG, to determine how to display the picture (ie: full frame or widescreen), is that done based on the PAR value or ratio flag?

Both, 720x480 and 720x576, the full DvD resolutions for NTSC and PAL respectively, support, both, 4:3 and 16:9.

In this case, as the SAR is the same for both fullscreen and widescreen, but the DAR is different, the PAR would also be different, I would think?

As an aside, nothing to do with my original question, but it would appear then that while a 16:9 picture is actually wider than a 4:3 picture, but because it is made up of the same physical number of pixels at the 4:3 picture, the 16:9 would contain less detail?

And to think I thought this would be an easy exercise......................

Thanks so much,

Hugh

[hcowan]

Regarding bitrates: use a reliable program like GSpot or Bitrate Viewer. Those actually read through the entire file and report the bitrate. Most other programs just look at the header which may no reflect the true bitrate.

Thanks so much for recommending GSpot and Bitrate. I had previously never used the programs before and found them very, very helpful!!

Hugh