VirtualDub help - Processing: Rendering and saving the processed output
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... | Once the source video has been edited as necessary and appropriate processing parameters set, the video can be rendered to generate the final result. This can either be previewed live or saved to a file on disk. ## Previewing the edited result The File > Preview output from start... command begins rendering the timeline to the video display so that it can be previewed. Most video and audio processing operations are active in this mode, with the notable exception of audio and video compression, which are disabled. The result that is seen in the output display pane and heard from the system speakers is thus representative of the output of the video and audio filter systems, but may be of higher quality than what would be stored in compressed form. Rendering filtered audio and video in real-time consumes a lot of CPU power and in many cases VirtualDub will have difficulty attaining full frame rate given a complex filter chain. When this occurs, the audio may lose sync and begin to stutter as the video frame rate drops below real-time, since all video frames are still displayed. The Option > Drop video frames when behind option can help here by allowing VirtualDub to process only a portion of the video frames in order to maintain real-time performance. This only affects preview and does not remove frames during any save-to-disk operation. Note that this may not be sufficient in extreme cases where the audio chain or the hard disk is unable to attain real-time either. The Sync to audio option also affects preview by changing the way that VirtualDub synchronizes audio and video playback; it should normally be left on, but if there are problems with audio timing that prevent synchronized playback from occurring, disabling this option may allow preview to proceed. Like the option to drop frames, this option too only pertains to previewing and does not affect renders to disk. ## Saving the processed result to disk File > Save AVI... starts a render process to disk. A new AVI file is then generated containing the processed video and audio. VirtualDub is normally able to write AVI files larger than 2GB using a extension to the AVI file format called the OpenDML hierarchical index. This is done in such a way that older applications that do not understand the hierarchical index can still open the first 2GB of the file. However, occasionally an application cannot open such AVI files at all. The File > Save old format AVI command disables VirtualDub's use of that extension so that only an original-format AVI is written. Note that this format does not support AVI files larger than 2GB, so care must be taken to appropriately trim or compress the video to fit below this threshold. If only the audio is desired, the File > Save WAV... menu option produces an audio file on disk using the WAV format. All audio options are active, except for the interleaving interval, which does not apply since no video is being written. Video is not processed in this mode. Note that audio compression is active since WAV files can either be compressed or uncompressed, so be sure to disable audio compression if an uncompressed WAV file is desired. Although VirtualDub can read MPEG-1 files, it is not currently able to write them, even in Direct mode. ## Analysis passes Some video filters and video codecs may require analysis passes in order to effectively filter or compress video. In the analysis passes, the video is scanned to determine difficult areas of motion or other features; knowledge of the entire video can then be used to optimize the final output. This is known as multi-pass processing. For various reasons, VirtualDub does not know that a multi-pass operation is required by a video filter or codec and cannot automate the process. However, the File > Run video analysis pass assists in running analysis passes by running the video pipeline without writing a dummy file to disk. The audio pipeline is disabled as well for additional speed.