Difference between encoding and transcoding?

[JamesB69]

I was just testing Intervideo DVDCopy 3 and I backed up a film that was 2 hours 8 minutes long onto one DVD+R...

The final output had a resolution of 720x480 and a bitrate of ~2700kbps! The picture quality was barely distinguishable from the original when viewed on a 21 inch CRT.

How does this work, if I were to do an encode with say CCE or Tmpgenc at this resolution and bitrate, I do not even want to know what it would look like.

I want a standalone encoder that can utilize this technology.

[ZippyP.]

...I backed up a film that was 2 hours 8 minutes long onto one DVD+R...

The final output had a resolution of 720x480 and a bitrate of ~2700kbps!

I don't know how you calculated the bitrate but when I plug 2 hrs 8 min into a bitrate calculator I get 4500 kbps. No way full dvd res at 2700 kbps looks like the original on any TV, unless the original is crappy to start out.

[JamesB69]

for some reason the program only filled 3.96GB on the disc, and i got the bitrate from VirtualDub...

It also has 4 Audio tracks, which leaves a lot less space for the video....

[DoubleShadowIce]

http://forum.doom9.org/showthread.php?&threadid=63587

[guns1inger]

The original must have been shot on a super-8 with the lens cover on.

[skebenin]

On the contrary. You will occasionally find a video that looks extremely good at low bitrates. Spirited Away for example retains excellent quality even encoded (not transcoded, but encoded) with an average bitrate below 2,000. I know it's hard to believe, but it's true.

That said, in most cases if a video looks good transcoded at a certain low bitrate, it will look as good or better encoded at that bitrate.

For this discussion, transcoder means Compressed Domain Transcoder. It doesn't actually compress the video data, merely increases the existing compression by re-quantizing the DCT data.

Encoding is completely different. With an encoder, you feed it raw video data, and it does everything. It compares one frame to the next (and previous) to get motion vectors and delta, it transforms the frame using DCT, it quantizes the DCT data, etc.

As a transcoder (compressed domain transcoder) is not capable of performing all the steps required to compress raw video data, you will never get an encoder based on transcoder technology. It's almost a contradiction in terms.

[MackemX]

Spirited Away is a cartoon isn't it?

as skebenin mentions video content also has an effect on the output. Imagine a high action movie with many changes scenes and colours

what was the original bitrate?

personally, I wouldn't judge the quality of DVDCopy3 based on just one movie only test . What was the quality setting it used out of 5?

[JamesB69]

DVDCopy used the quality setting 3.
I found a few things I do not like about DVDCopy, and did a comparison using DVDShrink.

DVDShrink used up the entire disc, and the quality seemed a little better in some scenes and a little worse in some scenes, but the differences were only noticeable when doing screen captures. I also compared with the original, and they lose some sharpness, but not a whole lot.

I did a re-encode of the original at 720x480, 2pass VBR of 2700, and it looked pretty bad, blocks everywhere...

[skebenin]

Really? What encoder did you use? Did you encode the whole movie or just one part, perhaps a high action part? Did you preserve a 24 fps frame rate or convert it to 29.97 fps? Are you certain the trascode brought the average bitrate down to 2700?

I think some of the transcode supporters (perhaps ddlooping) would like to know about a disk that transcodes significantly better than it encodes. If you don't mind my asking, what disk was it?

@MackemX
Spirited Away is a cartoon. It may not be intuitive, but cartoons are often very hard on MPG encoders, especially anime with its penchant for extreme action scenes with none of the natural blurring of motion (though more recent titles seem to be adding a more natural blurring to their action scenes). The hard transitions and clean black lines mean lots of high frequency coefficients in the DCT, which is bad for compression. I was surprised when DDogg told me Spirited away needed only 1,893 to retain good quality, suprised again when I confirmed it for myself, and surprised yet again when I encoded it and saw the results.

[Gurm]

Animation is difficult no matter what. If it has lots of clean lines and low-motion scenes, it's hard to compress for the reasons just stated.

If, however, it has lots of action and detail, then it's like a REAL movie only worse.




- Gurm

[JamesB69]

I used Tmpgenc 2.5, and I encoded the first main VTS, which was 1GB, so it was severl scenes.

I kept all aspects the same as the original, (720x480, 24fps progressive).

If I get around to it, Ill post some screenshots, but dont necessarily count on it....

[akrako1]

I would think that cartoons would compress BETTER than normal video for the simple fact that there tends to be large blocks of homogenous color in the backgrounds, or even the foreground (simpsons, south park, family guy for examples). I understand that some aspects of compression involve representing a large area of homogenous color as a single area (or block) to save information for - thus saving lots of space. Wouldn't animation be much better at this type of compression, versus a 'real' camera shot of a background, with natural color gradients and detail?

[Gurm]

akrako1,

Yes and no.

LOSSLESS compression is very effective on cartoons, because it is often a variation on RLE (run-length encoding). You'll see a gigantic block of red reduced to "red x 1000". But DVD's, being MPEG compression, are LOSSY. Specifically, what transcoders act on is the TRANSFORM data - or what changes from scene to scene. If nothing changes from scene to scene because it's mostly just big blops of color, there's LESS for a transcoder to work with, which is why cartoons get mangled so much with DVD Shrink and whatnot.

You can certainly RE-ENCODE cartoons very efficiently - especially anime. Modern animation, though, can often be just as detailed as a "real" shot. Try compressing "Finding Nemo" and you'll find out.

[akrako1]

ah... makes sense - and thanks for the info. I was thinking more of traditional hand drawn/painted cartoons - more than cgi. I'll have to move away from DVDShrink to DVD2ONE with CCE for my cartoons... thanks again.

[Gurm]

Well it depends. For modern CGI cartoons, transcoding is just as good as it is for "real" films.

But for older stuff, it's best to do as you said and switch to DVD-RB.