The capturing process starts by selecting "Capture | Setup" from the main menu or "Setup" from the program toolbar. The Capture Setup dialog box will display with a list of the active DV cameras on the system. The user selects which cameras to collect data from, along with additional information such as the names of the files for saving captured data and the time period for data capture. Then a preview window will appear for each selected camera with the live data displayed. Recording the selected cameras is initiated by clicking on the "record" button on the program toolbar. Capture proceeds until either the previous specified time period has elapsed or the user clicks the "stop" button on the program toolbar.
When the capture process completes or is terminated manually, a summary report of dropped frames is displayed The data can be simply saved as is without any synch or trim of the data or a synch and/or trim can be applied before saving the data. The captured files can be recalled and synch/trim processing can be performed at a later time. Additionally synch times for the captured data can be determined either automatically or manually and the video can optionally be trimmed using specified times before and after the synch event.
When automatic synch is selected, the software scans the audio track of each sequence and detects a clearly defined audio event. The onset of this audio event becomes the synchronizing point for the video sequences. Since audio is typically sampled at 32,000 hz the synchronizing point can be identified with a high degree of precision, much greater than the typical 60 hz of the video. In the event that the software cannot detect the synchronizing event or if the wrong audio event is detected as the synch, the situation can be corrected using the "manual synch" option described later. Upon completion of the automatic synch detection, the first, synch, and last images are displayed for each captured sequence. The first and last images refer to the first and last images to be saved. If trimming was selected these would correspond to the images at the specified time before and after synch. A Video/Trimming control allows the user to adjust the first and last images to be saved and the control also allows the user to manually synch any of the captured sequences.
When manual synch is selected at the completion of capture, the software proceeds directly to the display of first, synch, and last images as described it the preceding section, skipping the analysis of the audio track. The user can then use the manual synch option to locate the synch event for the video sequences if so desired. When "Synch" is selected from the Video/Trimming control the software enters its "Manual Synch" mode. A dialog appears which displays the video and audio data for the selected video sequence along with a control. One window displays the video images. Another displays the audio as a graph of activity vs time. A marker on the graph indicates the current synch time and the image corresponding to this time is displayed in the video window. The control displays the current synch time and the corresponding video image number. Also there are buttons that control the "current" synch such as rewind, fast forward, step forward, step reverse, and play. When "play" is selected the audio plays through the speakers as well. There are also buttons that control the zoom for the audio data in the graph of activity. One can have the software locate the synch event in a specified time range. A range is selected by clicking and dragging the mouse on the audio activity graph. The selected range will be displayed on the graph as a different color. Then press the "Locate" button and the software will search only the selected range of audio for the synch event. This function is useful in the event that the are multiple events on the audio track and the "auto synch" locates the wrong one.
Saving the Data
To actually permanently save the captured video, select "Ok" from the Video/Trimming control. The video clips will be saved with whatever trimming was specified and the synch time will be properly stored. At this point the files are ready to be digitized with the Digi4 module. Upon completion of the save operation the captured files will be displayed as described in the next section.
Processing Saved Video Sequences
When CapDV saves a set of captured video sequences a naming convention is used so that the files can be easily identified as a group of related files. The user supplies a base name and the software suffixes this base name as follows: basename.cam1.avi, basename.cam2.avi etc for the cameras active for capture. To recall previously captured video clips, select "Playback | Setup" from the main menu or select the "Playback" icon on the program toolbar. Then click the "select" button and the standard open file dialog will appear. Select any one from the set of captured files. Then from the playback setup dialog check or uncheck the individual files as appropriate. When "Ok" is selected a window will appear for each video clip much as a live video window was displayed for each camera during the capture process. Then to synch or trim the clips select from the main menu "Edit | Synch/Trim" or "Synch-Trim" from the program toolbar. From there everything proceeds the same as when dealing with live video. The data can be synched either automatically or manually and optionally trimmed.