data rate, bitrate, irate: quality loss DV to DVD?

[maxfrost01]

The original 60 min DV is a 13 GB AVI file.

If I click on properties of this file it says "data rate 28,754" and "total bitrate 28,754" (so what's the difference?)

If I click on an edited clip in the timeline (taken from that same AVI file) it tells me that the data rate of that clip is 1,350.46 kbps. (so where did the missing 27,400 go?)

I create a 30 minute DVD burning at 7000 kbps (standard default setting)

I end up with a DVD that is 25 mins long (approx) and takes up 1.44 GB on the disc. (How come AVI was 13 gig for 60 minutes but it's only 1.44 gig for 25 minutes by the time it gets to the disc?)

If I import a chapter from the DVD and click on the clip in the timeline the bitrate is 7,000 kbps.

Here are the questions:
1. How come the bitrate of a clip in the timeline is so low? (1,350)
2. If the bitrate starts at 28,754 and ends at 7,000 am I losing a lot of potential quality on my DVD? The quality of the DVD is okay but not great.
3. Should I set the bitrate higher than 7,000 when burning?
4. What is the meaning of life and is there a tutorial that will give me the answer?

[lancecarr]

Hi Max,
1. How come the bitrate of a clip in the timeline is so low? (1,350)

The original file is in a format called DV AVI. It records relatively uncompressed (but not totally...befre anyone jumps in here!) at 25 mbs. Never changes. I too have never understood the file properties reported for DV AVI files both in VS and by Windows. Best to let it go. Just remember, DVD AVI 25mbs.


2. If the bitrate starts at 28,754 and ends at 7,000 am I losing a lot of potential quality on my DVD? The quality of the DVD is okay but not great.

The reason for the reduction in size is that you are taking your 25mbs DV AVI files and converting it to MPEG2 to satisfy the DVD standard. So you went from 25mbs down to 7000kbs,=smaller file.


3. Should I set the bitrate higher than 7,000 when burning?

8000 is the general consensus for highest quality DVD.

4. What is the meaning of life and is there a tutorial that will give me the answer?
Simple Max, the meaning of life is the setting and achieving of known goals by overcoming sufficient barriers to make the achievment of the goal rewarding. The goal, once achieved, must then be replaced with a new goal. No goal, you die.

[maxfrost01]

So just to check that I understand you correctly.........

1. Yes, I do lose a lot of quality when I go from the DV AVI to the DVD standard - and so does everyone else. This is normal and I should not take it personally. Sometimes video life just sucks.

2. The fact that I want the answers to my questions is of itself a goal and therefore there is happiness & meaning within my frustration.

Now can I walk on rice paper without leaving a footprint?

[lancecarr]

1. Yes, I do lose a lot of quality when I go from the DV AVI to the DVD standard - and so does everyone else. This is normal and I should not take it personally. Sometimes video life just sucks.

Actually no. Stock standard DV AVI should convert to MPEG2 for a DVD at about 8000kbs without noticable loss. You would have to post your workflow here and the exact files properteis and project properties so we can take a look at where it is going wrong.

2. The fact that I want the answers to my questions is of itself a goal and therefore there is happiness & meaning within my frustration.

Yes and no, there is happiness in the overcoming of the barriers but the big slice comes when you atain the goal.

Now can I walk on rice paper without leaving a footprint?
Depends on whether you walked in dog poop.

[maxfrost01]

LOL

But let me stay with the quality thing a moment longer..........

Here is my logic:

Fact 1: bitrate is the key determinant of image quality
Fact 2: bitrate falls from 28,754 to 7,000 kbps
Conclusion based on facts 1 & 2: I am suffering a major loss of quality

What am I failing to understand, master?

[Devil]

The answer is compression methods.

DV is I-frame compression throughout; that means each frame is complete in itself, taking quite a bit of file real estate.

MPEG-2, which is the basis of DVD, consists of a compressed I-frame only once every ½-second (roughly, with standard DVD-compliant encoding). All the other frames are P or B frames, respectively containing only the differences between it and the previous and next I-frames. With slow-moving scenes, it is clear that the differences are small, so the bytes of data needed are small.

So, we now come to bitrate. The default compression method is, IIRC, 7000 kbit/s VARIABLE bitrate. This means that fast-changing scenes (in reality, mostly transitions and similar effects) are encoded at about 7000 kbit/s and the slower moving scenes may be down to, say, 4000 kbit/s, ie a higher compression, therefore a poorer quality. Theoretically, this is not noticeable in normal viewing because the resultant artefacts are minor. Now, variable bitrate is useful to help squeeze long projects (>90 mins) onto a SD DVD. However, your 25 min project is not long, so you have no need for the extra compression offered by using a variable bitrate. Change your settings to 7000 kbit/s CONSTANT video bitrate.

I have calculated that 1.44 Gb over 25 min works out at 8053 kbit/s but this includes your audio as well as video. My guess is that you are using uncompressed audio which works out at a tad more than 1500 kbit/s, so your average video bitrate is about 6500 kbit/s which is surprisingly high for a VBR (are you panning a F1 race?). I therefore suggest that a 7000 kbit/s CBR will be only a marginal improvement, possibly unnoticeable. I suggest you may care to consider using Dolby Digital (AC-3) audio compression when you encode at, say 192 kbit/s for 2/0 stereo. This will give you much more space for longer projects.

As for 8000 kbit/s, I do not recommend it: you are getting into the hairy zone where many DVD players have difficulty decoding DVD¡ÓR/RW discs, which are much more difficult to read than commercial pressed discs. Some players are OK, others aren't. This is especially so if you intend to diffuse DVD¡ÓR discs to 3rd parties who may not have the same equipment as you. For best results choose quality (reliably named) blanks and always burn them at half their rated speed or less.

Finally, there is a lot of codswallop talked about how high bitrates are so much better. Did you know that most Hollywood blockbusters are encoded at an average 4500-5000 kbit/s VBR video bitrate? OK, the encoding process used by them is not the same as you have and you don't have a 6-figure $ hardware 25-pass encoder allowing manual tweaking (that I know of ) or a hundred or so man-hours to encode a single film! Yes, they may go up, at times, to close to 9000 kbit/s and they may go down to 1000 kbit/s for static shots, and they can switch between the two from frame to frame. Low cost encoders cannot do this kind of thing, but my point is that good results can still be obtained at low bitrates.

[Devil]

Fact 1: bitrate is the key determinant of image quality
Fact 2: bitrate falls from 28,754 to 7,000 kbps
Conclusion based on facts 1 & 2: I am suffering a major loss of quality

Not necessarily so. As a complement to the above.

You have a hypothetical case of a still pic lasting one hour. You have 13 Gb of DV over 90,000 frames (PAL) or 151 kb/frame. You have the same scene with MPEG-2 style compression (not possible, just for illustration) with a group of pictures of 90,000 frames. This will consist of a first frame and a last frame of 151 kb each and 0 bytes for each of the 89,998 P and B frames: total file length 302 kb. Viewing quality: absolutely identical, even though the DV file is 45,000 times bigger.

OK this is an ultra-gross exaggeration but it should give you an idea.

[lancecarr]

Hi Max,
Devil has summed it all up pretty well there.
In doing a conversion to MPEG2 from DV AVI you really should not be getting any great degradation of the picture. Like I said, if you are then let us know the exact properteis that you are using to burn the DVD and we will see if there is something else going on here.

[maxfrost01]

With you all the way (and very helpful) until I got to the bit:

I have calculated that 1.44 Gb over 25 min works out at 8053 kbit/s but this includes your audio as well as video. My guess is that you are using uncompressed audio which works out at a tad more than 1500 kbit/s, so your average video bitrate is about 6500 kbit/s which is surprisingly high for a VBR (are you panning a F1 race?). I therefore suggest that a 7000 kbit/s CBR will be only a marginal improvement, possibly unnoticeable. I suggest you may care to consider using Dolby Digital (AC-3) audio compression when you encode at, say 192 kbit/s for 2/0 stereo. This will give you much more space for longer projects.

I'm not panning F1 so I don't know why the kbps would be so high. How do you do the maths on the rate? I'd be interested to know.
I guess your recommendation on audio would only be applicable when space on the disc is an issue (which it is not on this one but has been on others). Just checked the settings for the burn and audio is Dolby; 2/0 (L,R); 256 bit rate.

Really appreciate your help - I'm beginning to get it.

I guess all that stuff about encoding as an mpeg2 is something to do with keyframes?

Slightly surprised that as the Devil you have no comments on the meaning of life.

[maxfrost01]

Lance,

Have recently been guilty of blaming my editing/playing problems on VS when the cause lies elsewhere. I may be doing it again (and maybe not).

Just took a look at two almost identical copies of the video side by side. Did this by playing back two DVDs in the two drives I have. One was playing in WinDVD 9 (as distributed with VS12 Ultimate) and one played back in Media Player Classic. The picture in WinDVD is noticeably better and perfectly acceptable. Picture in Media Player Classic is not as good - slightly grainy/blurred. I then swapped the DVDs and got the same result - WinDVD gives me a better quality picture both times.
I also played one of the DVDs in Windows Media Player and, again, the picture was inferior to WinDVD9.

Didn't appreciate the application you use for playback could have a noticeable impact on the image quality. Or maybe there are setting I just don't know about.

Had any similar experiences?

[lancecarr]

I was thinking about that also. It is very dependant on what you are using for playback as software can use codecs from different developers. As far as WMP goes I feel it is a total pig for MPEG2 playback.
Will these DVD files be used for viewing on actual TVs? If they are then that is the real test.

[maxfrost01]

Lance

It wasn't WMP but WMC (Windows Media Center) that I was using - but both give a pretty poor image.

And I've just played back a DVD on my TV and it looks good - much better than on my computer.

As you say, it is very dependant on what you are using for playback.

Lance/Devil - many thanks for all your advice and help. It may look like I never had a problem in the first place but now I know that, and I have some understanding of how bitrates work.

Keep doing what you're doing - IMHO it is this forum that makes VS a good choice for video editing.