VirtualDub help - Capture: Timing dialog
Processing: Main UI Editing Filtering Rendering/saving Artifacts The pipeline Direct mode Display panes Frameserver Video filter reference Video shader reference Video capture Hardware setup Driver selection Audio setup Pipeline Filtering Info panel Multi-segment mode Timing dialog Performance Troubleshooting Dialogs: Video filters Video frame rate control Video color depth Video range Video compression Audio filters Audio interleaving Audio compression Audio conversion Audio volume Capture settings Preferences On a crash... | The Capture timing dialog allows control of the way VirtualDub matches video to audio during a capture operation. Video frames can arrive from the video capture driver with non-regular timestamps due to timing accuracy issues and interference with background tasks in the system; timing disturbances can also occur due to irregularities in the source video signal. During the video capture process, the varying timestamps have to be matched to regular frame slots in the output video stream. Drop frames when captured frames are too close together If enabled, VirtualDub discards frames that are spaced too close together for the output frame rate. For instance, three frames with timestamps 10ms apart (100 fps) cannot fit into a 29.97 fps stream. If this option is disabled, all captured frames are written to the output stream, which will result in desync from the audio unless frames are missing in other parts of the video. This option is enabled by default. Insert null frames when captured frames are too far apart If enabled, VirtualDub inserts dummy frames into the output video whenever captured frames are spaced too far apart for the output frame rate. For example, two captured frames spaced 66ms apart would have a dummy frame between them in a 29.97 fps stream. This dummy frame is identifiable in the video stream as a zero-byte frame and displays the same image as the previous non-dummy frame. If this option is disabled, frames arriving slower than normal will cause the video to lag behind the audio unless that is balanced by another portion of the captured stream has frames arriving too quickly. This option is enabled by default. Null frame burst limit Controls the maximum number of dummy frames in a row that VirtualDub will insert when captured frames are too far apart. This limits the amount of damage that occurs if timestamps in the video stream are wildly incorrect for a moment, such as a full day ahead. The default for this option is 10. Resync mode: Do not resync between audio and video streams In this mode, auto-resync is disabled: VirtualDub will not monitor the audio and video streams for timing discrepancies. This means that the quality of synchronization in the output video is dependant on the accuracy of the audio and video clocks; for example, if the sound device is recording slightly slower than the requested sampling rate, or the video capture device reports timestamps that are 0.1% too fast, the output video will be accordingly desynchronized. It is highly recommended that you enable auto-resync, as the audio and video clocks are never exactly identical unless both are being captured on the same device. Resync mode: Sync video to audio by adjusting video timing VirtualDub will speed up or slow down the video clock to match the audio clock. This will affect the number of frame drops and inserts in the video stream. If the audio clock is more inaccurate this will result in more drops/inserts; if the video clock is the worse one, this can sometimes reduce the number of drops and inserts. The amount of adjustment to the video clock is reported on the information side bar as the VT adjust field. Resync mode: Sync audio to video by resampling the audio to a faster or slower rate The audio will be stretched or compressed to match the video clock. The video stream is not affected, but the audio stream will have a slightly higher or lower pitch and speed. As the discrepancy in clocks is typically very small, this change is not normally noticeable. This mode is only usable if the audio device is capturing in an uncompressed (PCM) format; if a compressed format is in use and this mode is selected, the sync video to audio mode is used instead. Note that this only applies to the raw audio capture format; any audio codec can still be used. The amount of adjustment to the audio stream is noted in the information side bar as the Resample field. This mode is selected by default. Correct video timing if it is off from real-time If enabled, the video timestamps are correlated against the real-time clock, and scaled accordingly if the capture timestamps are faster or slower than real-time. This can sometimes reduce the number of frame inserts and drops if the capture driver or hardware is using a time base that is not calibrated correctly. Automatically disable resync when integrated audio/video capture is detected Capture devices that have both audio and video capture integrated usually use a shared clock to avoid sync errors between the streams. When enabled, this option causes VirtualDub to automatically disable auto-resync when such a situation is detected. Note that VirtualDub must see both audio and video devices on the same capture driver for this option to take effect. If you are using a capture device which exposes its audio capture as a separate sound driver in Windows, VirtualDub will not see it as integrated.