neily
13th July 2004, 00:13
Hi,
I am curious to know where the frame time stamps come from when you capture a file, and what can influence them? The chain I guess is camcorder - firewire card - firewire driver - capture software, but what bits can affect the time stamp?
The reason why I ask is that I was getting a few dropped frames in camcorder captures both from tape and via passthough so I wrote a small applet to find the drops which analyses the subcode and vaux blocks in the files. As well as finding the odd drop which the capture programs didn't report, there were other occasional anomalies. For instance, with passthrough captures the vaux frame sequence numbers were occasionally out of sequence (0,1,2,3,4,5,6,4,8,9,10,11,0) and also there were occasions when despite there being a dropped frame (24 frames sharing a time code rather than 25), the frame sequence numbers were all OK. Obviously, being passthrough captures, the subcode timestamps are not defined, so I can't use them for correlation.
I am curious to know where the frame time stamps come from when you capture a file, and what can influence them? The chain I guess is camcorder - firewire card - firewire driver - capture software, but what bits can affect the time stamp?
The reason why I ask is that I was getting a few dropped frames in camcorder captures both from tape and via passthough so I wrote a small applet to find the drops which analyses the subcode and vaux blocks in the files. As well as finding the odd drop which the capture programs didn't report, there were other occasional anomalies. For instance, with passthrough captures the vaux frame sequence numbers were occasionally out of sequence (0,1,2,3,4,5,6,4,8,9,10,11,0) and also there were occasions when despite there being a dropped frame (24 frames sharing a time code rather than 25), the frame sequence numbers were all OK. Obviously, being passthrough captures, the subcode timestamps are not defined, so I can't use them for correlation.