Render Loss

boomhower wrote on 2/23/2005, 2:42 PM
I've read through some of the old posts on this topic but I recently noticed a loss in quality from my raw footage to DVDA. I'm using MPEG2 (I don't use the default choice) and used the batch render script for the first time on this particular project. Couple of Qs:

Does the batch render script have a known issue that might cause this? I went in and selected the appropriate DVDA mpeg2 ac3 settings under the batch command so I would think it would be the same.

How much quality loss is inevitable in the render process in a best case scenario?

The footage looked really smooth and clear in the preview but the quality loss was obvious to me while viewing the DVD although others claimed they thought it looked fine. I'm sure it stood out more to me because I had seen the raw footage and I'm a bit anal about little things like this. This falls under my "the person I made it for was thrilled but I'm still playing with the footage 2 days after delivering the DVD" category.


Keith

[edit] I did not use two passes on this.....but I haven't in the past either. Total vid was 8mins

Comments

johnmeyer wrote on 2/23/2005, 3:28 PM
Not quite sure of the video format for your source footage. I assume it is DV, not MPEG-2.

Quality for MPEG-2 encoding requires:

1. A bitrate above 6,000,000 (average bitrate). Some might disagree and give you a larger or smaller number. However, if you encode at 4,000,000 (average), it will definitely look far worse than the original.

2. The "Video Quality" in the MPEG-2 Custom section (on the Video tab), should be all the way to the right (High, 31). If it is not (which unfortunately is the case for the "Default" template), the video will look lousy.
boomhower wrote on 2/23/2005, 6:36 PM
Yes, the source is DV (PD170).

I'm using variable bit rate with max of 8 average 6 and min 192,000. Are you saying I should use a constant rate of 8 or continue with the variable but bump up the max and average?

Thanks....
John_Cline wrote on 2/23/2005, 7:31 PM
If your video is less that about 74 minutes and you're using 192 Kbit AC3 audio, then you can use CBR at 8 megabits/sec. Throw all the bits at it that you can. In fact, since the maximum bitrate spec of the audio and video combined is 9.8 Mbits/sec, if your video is an hour or less, you could go so far as to use a CBR of 9 Mbits/sec for video and 192Kbits/sec for the audio.

Keep in mind, however, some DVD players will choke on video encoded near the maximum bitrate. Also, MPEG2 encoders will sometimes spike above the set bitrate and, if you're pushing the limits, your video may may momentarily exceed the maximum allowed bitrate. As was already mentioned, always keep the quality slider all the way up at 31.

If you'd like to check the actual bitrate of your encoded video, there is a free bitrate analyzer at www.tecoltd.com. Very handy if you're looking for spikes.

John