Batch capture FAQ

Why is batch capture important?

Unlike manual capture, where you just play your tape and press Start Capture when you get to a point you want to start capturing, batch capture is a much more controlled process. You can type in the start and end timecode values numerically and control precisely what is captured. You might do this if you have logged your tape and decided which clips to capture offline, perhaps by viewing a VHS copy with burnt in timecode, and don't want to capture everything off the tape.

The main reason batch capture is important though is that it gives you a way of repeatably recreating a project. Captured DV files are huge, and unless you have infinite disk space eventually you will need to purge old media files from your hard disk as you move on to new projects. If you ever need to go back to an old project the batch capture command EditDV will automatically recapture all your source material, prompting you to insert each tape as it needs it. For this to work, EditDV needs to be able to locate the original position on tape again using the tape's timecode, as discussed in a separate topic.

The analogy for software developers is with source and object files. Your project file, and any auxiliary media such as Photoshop images or CD audio tracks that you have imported, are your source files. They are tiny in size compared to video files and should be backed up and may as well be kept indefinitely because they are so small. Your video files, on the other hand, are massive, and behave like object files: although the process may take a little while, they can be regenerated automatically from your source files. In the case of your program files by rendering, and in the case of your source media by doing a batch capture.

What is a capture log file?

If you have logged a tape offline and have a list of in and out points for the clips you want to capture you can use the capture dialog to type these clips in one at a time. You will probably find it more convenient to type the in and out points and clip names into a text file and import them using the Import Log command. The format of a capture log file is as follows, taken from Digital Origin's web site:
EditDVĒ Batch List 1.5
Event count=7

Tape ID	Name	In	Out	Tracks	Comments 
Data
Long Tape	1st Segment	00:00:04;29	00:09:04;29 VA1A2	
Long Tape	2nd Segment	00:09:04;29	00:18:04;29	VA1A2	
Long Tape	3rd Segment	00:18:04;29	00:27:04;29	VA1A2	
Long Tape	4th Segment	00:27:04;29	00:36:04;29	VA1A2	
Long Tape	5th Segment	00:36:04;29	00:45:04;29	VA1A2	
Long Tape	6th Segment	00:45:04;29	00:54:04;29	VA1A2	
Long Tape	7th Segment	00:54:04;29	00:59:59;29	VA1A2	Change this using Modify Log Entry 
As well as importing clips that you have typed into a text file or generated from an external application, you can also use a capture log such as this one to capture an entire one-hour tape in one go and then log individual clips on the computer. This needs more disk space but can avoid additional wear on your camcorder and tape. If you prefer, you can use CatDV to generate EditDV whole tape capture logs. Note that you must adjust the final out value so it matches the last timecode value on your tape; the capture will fail if you attempt to capture past the end of the tape.

What does the "Create Log from Program" command do?

The Create Log from Program command can be useful for reducing the amount of disk space used by a project. It's useful if you tend to capture long primary clips (eg. if you use a whole tape capture log) but only find yourself using short sections of the captured material in your program. If you start running out of disk space then it can be quite frustrating knowing there's a 5 minute (1Gb) file on disk, say, of which you only need 15 seconds!

This is where Create Log from Program comes in. Effectively, it creates a completely new EditDV project from your old project, based on a completely new set of primary clips. There is one new primary clip for each clip segment used in your program. If you delete and detach all the original long clips from your bins and then do a batch re-capture you end up with just that material needed by your program, probably taking up a fraction of the original disk space.

The best place to do this is once you've already done a reasonable first cut of the editing, because if you need to add any more material to your program you'll need to capture it again. It's also a very good idea to back up your project before you do Create Log from Program, because the changes it makes to your project are pretty dramatic and irreversible! It's usually worth it though because of the disk savings.

Two minor annoyances with Create Log from Program are that all your clip names end up with an ugly ".1" appended to them (to distinguish the new files from any old ones after batch capture, I guess) and that you need to do an additional batch capture. Theoretically it should be possible to slice and dice the original long primarily clips into shorter ones in situ, without having to recapture them, but if you've already run out of disk space I guess it might be quite difficult to implement this reliably.

What common problems can occur during batch capture?

The problems that can occur if your source tapes don't have continuous timecode are discussed in a related topic. (Timecode is vital to batch capture as it's how the material to be captured from tape is identfied.)

Other errors are similar to those that can occur with a manual capture, eg. dropped frames, late interrupts and so on, which are all indicative of a system with insufficient performance, or more likely which hasn't been configured properly. If you get capture errors you should follow the advice given in the EditDV manual and support pages on the D.O. web site.

One point to note specifically regarding batch capture is that if an error does occur, details of the error aren't reported on the screen (only a summary saying something like "0 of 1 clip(s) captured successfully"). Instead, you need to refer to the separate error log file that's created on your hard disk (in the same directory as the project file) to find out what happened.

Also, because batch capture is all about repeatability, it tends to be stricter about conditions which are only warnings during manual capture. It's not obvious but the dialog option to ignore discontinuous timecode errors only applies to manual capture, for example, not to batch capture!

Problems with audio during batch capture

There are a couple of peculiarities related to what happens to the audio track during batch capture. These problems seem to be specific to the Mac version of EditDV.

One problem is a bug that can cause a "couldn't capture clip because it has the wrong number of tracks" error to be reported. If you look at the captured clip you'll notice it has a video but no audio track. There is a simple workaround for this problem: open the offending clip with the Modify Log Entry command, then press Ok without changing anything and recapture. (This bug has been fixed in later versions of EditDV.)

The other problem is just as uncommon, but rather more insiduous because there are no obvious symptoms to alert you to the fact that something has gone wrong. For performance reasons and to fit in with the QuickTime architecture, as part of the process of capturing a DV clip a separate QuickTime audio track is generated. On systems with borderline performance there is a possibility that this audio track becomes corrupted slightly, whereby the audio track is shortened compared to the video track. If you place one of these corrupt clips on your timeline then from the point of the corruption onwards you may experience audio synch errors where the audio precedes the video. (Note that this is different from the well-documented behaviour when previewing out firewire, where the video and audio follow different paths and have a fixed delay between them.)

If you suspect you might have clips with a corrupt audio track you can check by opening the clip in QuickTime Player (Pro version) and doing Get Info to compare the length of the video and audio tracks. If they differ you should delete the clip and recapture it. You can also use CatDV which can be configured so that it reports differences between the audio and video length of any movies that it imports. The workaround to recapture any corrupted clips is simple and effective, as long as you recognise what is going on!


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