Ori Pessach wrote: > > Congratulations! > > It's not everyday that I read a technical description that causes me to cringe to > the point of physical discomfort. I'm impressed. > > Now, please don't take this personally, but this is simply the wrong thing to do. > Dropping audio, or "padding" it is definitely going to be noticable. I heard > off-by-one errors, resulting in just _one_ sample being set to zero, causing > audible clicks on buffer boundaries. Think of what you're doing to the frequency > spectrum, around the edges of the padding: basically, you're introducing a lot of > high frequency noise at the point of transition. Dropping samples causes a > discontinuity in the time domain, which translates to, again, high frequency noise > in the frequency domain. > > If you're looking for a quick and dirty approach, you're far better off dropping > or repeating the occasional video frame, instead. I guess the absolutely correct, > anal retentive thing to do would be to keep the video time line as the capture's > main time line, and resample the audio to stretch or squeeze it, so it tracks the > video. Not very easy to do without introducing some aliasing artifacts, but > certainly possible in real time. The only tricky part is determining by how much > to stretch. > > On the flip side, this approach will, indeed, maintain perfect synchronization. I > just feel that the tradeoff is unaaceptable. > > Ori Please don't knock it before trying it. 1) I don't pad with zeros - I said you duplicate the last byte. Yes, this still does introduce some distortion, but it is almost inaudible. 2) Dropping blocks does lead to clicks. Fortunately, the clicks are single sample, and are filtered out almost completely by the reconstruction filter of the sound card. 3) Dropping/duping video frames is perceptually worse (at least from what I have seen) than manipulating the audio. (You get regular jerks in video playback, where by manipulating the audio you get regular sub-perseptive audio distortions.) Just try the technique, and listen to the results - I am sure you will be pleasantly surprised (Oh yes - don't listen to the results with qtplay - it sucks). And by the way, all my high quality capture applications use post-filtering+stretching to match the streams. This technique is only supposed to be use for vcr-like applications, where it is more important to get a once-off recording, than absolute quality (in which case you wouldn't be using streamer anyway). -justin
