Entering Video Bitrate Makes Preset Switch To SVCD

[akulier]

Strange thing:

When I try to convert a DivX into a DVD, the video bitrate is preset to 4000, and shows in green. When I press Best, a new rate is calculated (e.g. 2700), again in green. When I then change it back to 4000, it shows in blue, and the preset in the summary autmatically switches to SVCD!!!!!

So, what do I do to get the best possible quality of a movie, using the full space of a DVD4, without having the thing select SVCD by itself?

Please help me!

thx a lot!!!

Alexander

[akulier]

To clarify:
when I enter the bitrate MANUALLY, it does NOT switch to SVCD, but when I hit the RATE button, the automatic switch happens.

[Case]

The developer will have to fix that in a future version, I guess. But after getting the bitrate right, you can set it back to DVD by selecting the DVD Profile in the Options tab.

[akulier]

The problem still is that it is not recommended to crank up the bitrate too much beyond the "Best" rate which I don´t understand, but follow. To me, it seems like a waste to burn a 700 MB movie onto a DVD-R and leave the rest empty.

What does happen if you increase the bit rate like 2-3fold over the Best rate?

Alexander

[Case]

Set-top DVD players are certified for a maximum bitrate of about 10000 kbps (could be 9800), so that there is a defined read speed that all players should be capable of. This is for pressed 'silver' DVDs (pre-recorded), which are easy to read. A movie wih a higher bitrate would not be a DVD®, because it doesn't meet the DVD specification.

If you burn a 10 Mbps movie to DVD-Recordable, then a set-top DVD player might have trouble reading it so fast. DVD-Recordable uses different material, and is not as easy to read as a store-bought movie on DVD. Some research says DVD±R(W) should stay below 6500 kbps for good compatibility.

This bitrate maximum is the total bitrate of video, audio and subpicture streams. The bitrate in ffmpegX's Bitrate Calculator is for the video only (hence the field name "Video Bitrate").

--
A second thing to note is what bitrate is needed to encode your footage. What is needed might be a lot less than 10 Mbps.
- DivX 512x384 to DVD 720x576 is upscaling, so the frame only holds so much information to encode, that is, the finest details in the movie are larger than the finest possible for DVD, requiring less bytes to describe them.
- Original film to DVD to DivX to DVD is 4rd generation of lossy encoding, so a lot of the finer details, like grain/noise, which are hard to encode, are lost already. 'Softer' footage is easier to encode.
- If you set the bitrate way too high, then ffmpegX won't use all of it: If a frame can be described at best quantizer level using X bytes, where X is below the bitrate maximum, then what should the encoder do with the remaining bytes? It just doesn't use the remainder.

[akulier]

Thx a lot, now I am getting the idea.

All I really wanted is to crank it up from 935 to let´s say 1400, 2000, 4000 or whatever. Does that make sense or is it just a waste of time and computer power without increasing quality?

After all, the manual says NOT to increase the picture size.

Alexander

[Case]

DivX (mpeg-4 asp) uses a more complex encoding scheme than MPEG-2 (DVD). DivX was designed to get better quality at lower bitrates than other codecs before that, including MPEG-2. So when you encode from DivX 935 kbps to DVD, the needed bitrate will be higher. The default bitrate in ffmpegX for any full resolution DVD preset is 4000 kbps, which is a bit above the [Best] bitrate, so to make the default work in all cases. That is, if you go with default settings, the DVD will look fine, bitrate-wise.

For a PAL DVD (720x576, 25 fps), the [Best] bitrate suggests 3746 kbps. The number stays in green ('good') between 3372 and 4120 kbps. You could set it to 6000, and everything would be okay, but the quality will possibly only be a tiny bit better compared to 4000 kbps. Maybe you can't even tell the difference by looking at it.

Some scenes are harder to encode than others, so some movies may benefit more from a higher bitrate than others. Things like high speed motion, erratic motion (fire, water waves, etc) and noise (analog dead tv channel) are hard to encode, because the movie frame don't look like the previous frame, which requires more data to describe them.

All I really wanted is to crank [the bitrate] up. Does that make sense or is it just a waste of time and computer power without increasing quality?

The bitrate setting doesn't change the encoding time or required CPU cycles that much; the only thing possibly wasted would be disk space.

After all, the manual says NOT to increase the picture size.

The DVD specification has very strict rules on frame size. Only a limited list of resolutions are allowed.

[akulier]

Well, I have settled on just burning the DivX Files on a data DVD and using a DivX certified standalone Player. Before that, I do a "conversion" Avi - Avi DivX with a little bit higher bitrate and fixed subtitles.

The result is really fine, even on a 42" HD TV (which is usually pretty unforgiving when it comes to bad quality). Today, I will try it on my videobeamer.