Problem rendering video

Gigi wrote on 8/18/2009, 2:52 PM
Sorry, this is rather long:
I have experienced an issue rendering a video into a wmv format, and I wanted to ask if anyone has any opinion where the problem may be .

I have a HP laptop with 4G of memory and 2.53 GHz Core2Duo processor, my harddrive is 7200RPM. I am relatively new to video editing. Not too long ago I worked with a short video, the soundtrack on which is a timecode that is meant to drive the corresponding MIDI file on a Yamaha Disklavier piano. The quality of the soundtrack, therefore is absolutely crucial, because even the slightest distortion in the sound will affect the relationship between the time code and MIDI file and thus the resulting playback. The video (and audio) worked just fine when I was working on it in Vegas ( I had my computer connected to the Disklavier and I tested things out throughout editing process), but after I rendered it into WMV, the playback using that new video file was distorted, and the MIDI file was not playing properly. I think something happened in the rendering process.
What do you think caused it?
Is it the format into which video was rendered? (I probably can experiment with different formats, when I have the time).
Could it be that my computer is not powerful enough to deal with rendering process?

Any insight and help would be very much appreciated.
Gigi

Comments

Chienworks wrote on 8/18/2009, 3:01 PM
WMV files usually have less than wonderful audio. Most of the available bandwidth is used by video. You can go into custom settings when setting up the render and choose a much higher bitrate for the audio. However, no matter how high you raise it you'll still be dealing with compression which adds distortion and artifacts.

I guess the obvious question is why don't you include a recording of the piano as the soundtrack of the video file?
Gigi wrote on 8/18/2009, 3:12 PM
I actually was aware of the audio issue with WMV files, so I made sure that my audio settings were decent. Audio: 64 Kbps, 44,100 Hz, 16 Bit, Stereo. Also, the interesting thing is that the problems with the soundtrack are not consistent. Altogether I did 6 videos, two of them were flawless - no distortions. The other 4 had issues in a few spots, not prevalent, but quite noticeable.

To answer your last question is that these video/MIDI file combination produces a far superior musical experience. Once the sound is recorded in audio, so much of the playback depends on the equipment being used in the playback scenario. With my set up: video with timecode that drives MIDI file on the Disklavier: The image of the performer is displayed on the screen, while the sound of the performance is produced by a concert grand, acoustical piano (in this case Yamaha Disklavier).

Do you think my problem will be solved if I did try a higher audio resolution for Render? Or do I have to beef up my system?

Thanks
rs170a wrote on 8/18/2009, 3:36 PM
Your laptop should have no problems playing back DV-AVI files.
Picture and sound will be both be much better than WMV.

Mike
PerroneFord wrote on 8/18/2009, 5:33 PM
* Audio: 64 Kbps, 44,100 Hz, 16 Bit, Stereo *

I use settings higher than these for spoken word. Change the bit-rate to 320kbps at a MINIMUM. Heck, even iPod audio is usually 128 Kbps or higher.

Chienworks wrote on 8/18/2009, 6:25 PM
Yep. MP3 can be acceptable for background noise at 64Kbps. WM*[VA] doesn't even get up to scummy until you pass 128Kbps.
MarkWWWW wrote on 8/19/2009, 6:07 AM
> The quality of the soundtrack, therefore is absolutely crucial

Indeed it is, for this sort of application.

Unfortunately that is where the problems begin. The timecode audio signal is not intended ever to be listened to by the human ear, and if you do listen to it you will hear that it isn't at all musical sounding - it's a very unpleasant squawking noise made up of very rapid shifts between a couple of frequencies, representing the ones and zeroes of the underlying time code.

In order to detect and decode the information carried by the audio timecode signal, the detector relies on the audio signal having quite tightly defined phase properties. Interestingly, (static) phase is something that the human ear is very insensitive to indeed and this is where the problems start when you try to put audio timecodeinto a video file. Most video formats use lossy compression for their video and audio signals as this allows the size of the file to be reduced dramatically with only a small effect on the percieved quality. All lossy audio compression schemes work by throwing away the information that is least important and only keeping the information that is most important to the human ear. Unfortunately this means that most of the (static) phase information (which the human ear doesn't care much about) get thrown away.

The upshot is that an audio timecode signal is likely to be unusable after it has been through a lossy audio compression porocess like MP2, MP3, WMA, etc, even if quite a high bit rate has been used. To ensure that the audio timecode is able to be decoded from the video soundtrack you should choose a video format that allows uncompressed audio, sometimes referred.to as PCM, to be used. A DV .avi would be my first choice.

Mark