MPEG2

kdk2002 wrote on 6/17/2002, 11:38 AM
My question has two parts:

1. Why does it take SO LONG to render MPEG2 files in Vegas? Is there a standard ratio between an edited AVI movie length and MP2 conversion time? Transitions and effects along with added music really doesn't seem to lengthen the rendering process by that much over a "raw" AVI clip.

2. If I want record my movies to DVD from Vegas, do I have to use MPEG2, do I also have to use the "default" quality or can I reduce it (from a rate of 8,000,000 to 3,000,000 for example)?

I'm a beginner at this stuff, thanks in advance for any responses.

Comments

BillyBoy wrote on 6/17/2002, 1:37 PM
How long rendering takes is mostly a factor of how fast your CPU is and what you're asking to be done. Vegas Video takes longer to render then some other applications, but then again those "other" applications don't do as much as Vegas does or nearly as well. So look at the time of doing the WHOLE project not just how long it takes to render. Once you get use to using Vegas the editing portion can fly along.

Vegas Video comes with templates. Pick the appropriate one for the task you have in mind. For example if you're going to 'print to tape' ie record to a DV tape in your camera then you use AVI DV template. If you're going to make a DVD disc then you need to render to MPEG-2 and choose a DV template for that. While I haven't tried myself yet you can drop the bitrate. How well or if it plays back is more dependant on what DVD player you're using. If that's what you want you'll also need some DVD authoring software. Vegas Video does everything that needs to be done up to and including rendering the appropriate MPEG-2 compliant file, but it does not create chapters (menu system) or burn directly to DVD discs. Not yet anyway. <wink>
vonhosen wrote on 6/17/2002, 2:38 PM
Your maximum bitrate for DVD is 9.8Mbs. This has to include the video & audio in your stream.

You can encode CBR(Constant bitrate) or VBR(Variable bitrate). CBR does what you expect and provides a constant rate that you set regardless of how much action is going on. VBR will have a min,avg & max level. It will encode to those levels supplying higher rate where more action requires it and low level where little action is present. Some encoders will do multiple passes reading the whole file first to assess action & then encode on a 2nd or 3rd pass.
VBR generally takes longer & there is little to gain from VBR if your project is an hour or under.

You only have a limited amount of space on which to fit your project and in simple terms higher bitrate = higher quality. Dropping from 8Mbs to 3Mbs will see a substantial difference in quality.

The audio you use is going to impact on the available bitrate available for video.
NTSC base spec states for DVD it must support Dolby Digital stereo (otherwise known as AC-3) & PCM (Pulse Code Modulation). Dolby you can set bitrate at about 192Kbs and still have reasonble quality. PCM is uncompressed (.wav) file and it's bitrate is 1600Kbs. You can see that this is going to have a large affect on amount of video you can fit on your disc. you are going to have to cut bitrate for video or limit project size. The cheapest DVD authoring I know that supports AC-3 audio is DVDit PE (your looking at about $599 to upgrade from LE version which is OEM bundled with a lot of burners)

If your project is for PAL player you are lucky in that PAL spec supports MPEG-1 layer II audio. This has similar bitrates to AC-3 but programs that support it are cheaper to buy as there is no Dolby licencing fee to pay. DVD Complete by Dazzle is a great program that supports PCM & MPEG audio for $99.

I use the following formula to work out what rate is availble to me for encoding my video stream based on how long my movie is.

The safe, useable size for Video and Audio is 3.6 gigs. As shown below in the formula:

DVD: 36096 Mbits of safe useable space
Space for AC3 audio (at 192 Kbit/s)= (number of seconds in your video*192)/1024
e.g. audio for 2 hours, (7200*192)/1024 = 1350 Mbits
Remaining space can be allocated for video, 36096-1350 = 34746 Mbits
For 2 hour project: video data rate = remaining space/number of seconds in your video
e.g. 34746/7200 = 4.825 Mbit/s
If using PCM audio, substitute 1600 in place of 192 in the audio calculation.

Since it’s easier to calculate the minutes, rather than the seconds, here’s the formula:

For AC3 audio:

(36096-(((Length of Video in Minutes*60)*192)/1024))/(Length of Video in Minutes*60)

For PCM audio:

(36096-(((Length of Video in Minutes*60)*1600)/1024))/(Length of Video in Minutes*60)

VV3 built in encoder will give you good MPEG files & allow you to encode as a multiplexed stream or seperate streams to take them to whatever authoring program you choose.
kdk2002 wrote on 6/18/2002, 7:58 AM
Thanks for the detailed information!