There is no time limit on a DVD, just a capacity in bits and bytes. The more hours you want to squeeze on a disc, the less bits per second will be available and the lower the image quality will be.
Whether or not two and a half hours will produce an acceptable result depends on:
- The quality of your source material. Clean (little noise) video compresses better.
- The nature of the material. If there is relatively little movement, the MPEG encoder has an easy job. If there is lots of movement, or fine detail (like leaves moving in the wind), the encoder will need more bits.
- The quality of the MPEG encoder. Not all encoders are created equal. The encoder in Encore is quite good, but for more than 150 minutes you would probably better be using another encoder.
- How much of the available bit rate will be used up by the audio. Luckily Encore has an integrated Dolby Digital (AC3) encoder. AC3 stereo audio typically uses 0.2Mb/s, compared to uncompressed PCM at nearly 1.6Mb/s. On a 150 minute job that makes a huge difference: The total bit rate you can use is 4Mb/s - leaving 3.8Mb/s for the MPEG-2 video if you are using AC3 audio, but no more than 2.4Mb/s if you would have had to use PCM audio.
- Your expectations/standards. ;-) If you are only satisfied with the absolute highest quality possible on a DVD, the limit for a single layer DVD would be about 60 minutes. If you are happy as long as you can more or less recognize the original video, the same disc could hold 4 hours.
