converting from mp4 to mpeg2

[haytham501]

hello I have a mp4 video with frame size 1280*720 and data bitrate 4442 kbps and I want to convert it to mpeg2
if I convert it using the simple way in vs pro x6 through dvd then mpeg2 it will convert it with higher size and higher bitrate
what data rate should I put using custom then mpg files to keep same quality and size

[Ken Berry]

if I convert it using the simple way in vs pro x6 through dvd then mpeg2 it will convert it with higher size and higher bitrate
what data rate should I put using custom then mpg files to keep same quality and size

The question of quality and size are in fact the key, but not in the sense you might think. First off, mpeg -- be it mpeg-4 or mpeg-2 -- is a lossy format. In other words, every time you render it (and that includes conversion), it will lose some quality.

Next, mpeg-4 is much more highly compressed than mpeg-2. That's how they get a smaller file, though with the algorithms used, the quality remains high. But converting it to mpeg-2 means you are lowering the compression, so the resulting file will be bigger. And again you have to think of the loss of quality caused by the conversion in its own right. So to compensate, you need to use as high a bitrate as is consistent with mpeg-2. On top of that, you are going from high definition mpeg-2 (which is what 1280 x 720 video is) to what I am presuming is meant to be standard definition mpeg-2... or is it? You haven't in fact told us what you are wanting to make with the converted video. If it is a DVD, then that is standard definition mpeg-2, which will have a smaller frame size (720 x 576 PAL or 720 x 480 NTSC) which will notionally be of lesser quality than the original. And the highest quality you can achieve with that format is from a bitrate of around 8000 kbps.

Your original mpeg-4 has a bitrate of 4442 kbps -- which I have to say is relatively low for high def video. But converting that to standard def mpeg-2 using that bitrate I mentioned above (8000 kbps) means you will never be able to maintain the same size in the end video, even if the quality remains fairly high. One hour of such video would be around 4.3 GB.

The matter becomes even more complicated if, instead of DVD quality mpeg-2, you are talking about converting the mpeg-4 to high def mpeg-2 which in effect is Blu-Ray (leaving aside the question of HDV mpeg-2 though similar arguments apply). But again, you would be converting a highly compressed format to a format using less compression, and thus producing larger files -- and depending on the bitrate used (and bitrate determines quality), the end file would be very much larger that DVD-quality mpeg-2. You would probably also be moving from 1280 x 720 to 1920 x 1080 (0r perhaps 1440 x 1080) which will require in effect the invention of new pixels which is usually done by simply duplicating existing pixels (and thus producing further quality loss).

I can't say with any exactitude, but converting your original mpeg-4 to high def Blu-Ray compatible mpeg-2 would probably require roughly double, and probably higher, the original bitrate to maintain roughly a similar level quality. But the file size would be much larger than the original and the quality possibly less than the original.

[haytham501]

I want to convert the file to mpeg2 in order to watch it on my starsat receiver 6300 usb
the file has to be in 4:3 aspect ratio and frame of 720*576
I want to know if I put same data rate I will have same quality or should I put higher data rate

[lata]

Hi

Using Settings Make Movie Templates Manager create a new Mpeg2 Template
You are limited in using the industries standard properties for DVD
I assume you will be using 25fps, your Mpeg 4 could however be using 30fps?
You do not give full details of your video file, right click in the timeline and select properties, what are they?

These are typical settings for Mpeg2:-

MPEG files
24 bits, 720 x 576, 25 fps
Frame-based
(DVD-PAL), 4:3
Video data rate: Variable (Max. 8000 kbps)
Audio data rate: 256 kbps
Dolby Digital Audio, 48 KHz, 2/0(L,R)

The data rate of 8000 allows for 60ish minutes at 4Gb file size, this is high DVD quality, at 4000kbps is equivalent to VSH quality (2 Gb)

I chose Frame Based as your original Mpeg4 will probably be using that and not interlaced.

Aspect Ratio
May be a problem as your original is using widescreen 16:9 (1280 x 720)
If you convert to 4:3 either :-
1 / the frame will be distorted – people will look quite tall and thin.
2 / the left and right border can be cropped to create the 4:3 shape, you will lose that detail. (use the Distort option or overlay tracks to resize the frame)

Run a few tests using lower data rates to compare quality against file size.

[skier-hughes]

I want to know if I put same data rate I will have same quality or should I put higher data rate

You are converting it to a lower quality file, so you'll never get the same quality. A higher bitrate will, as has been said, help offset the losses.
If this is a one off, I'd plump for Lata & Ken's 8,000
If you intend to do lots of conversions, it's simply a case of you playing with the settings, gradually coming down lower and lower until you find the point where the quality drops off to much for you.
What I may find to low, you might find acceptable.