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720 24P timecode discrepancies in FCP
I am editing a show right now that is shooting DVCPRO HD 720p24 and capturing from a Panasonic AJ HD 4200 deck to Final Cut ver 5.14 via Decklink HD Extreme SDI capture card. We are editing in the native codec in a 23.98 project.
Yesterday we checked some clips in our project to make sure that their timecodes matched those of the tapes. While there have been no problems at any point in our project with FCP introducting duplicate frames, we found some discrepancies between the timecode of the offline footage and that of the tapes. It seemed that in some clips, all the timecode was frame accurate to what was on the tape, while in others a discrepancy of 1 frame was introduced onto the FCP clips every 5 frames. The discrepancy did not compound, it would correct itself after each occurrence.
To test how this would affect our eventual online, we created an EDL of a short sequence and then conformed the sequence from our masters. The result was that picture in some of the clips in the conformed sequence matched that of the the corresponding offline sequence perfectly, and others were shifted by one frame.
Someone advised us that the cause for our problems could be that we weren’t making a point of starting the capture of clips on A frames, or, even more specifically, on frames ending in “00”. So we looked at some clips that were captured starting on “00” frames and compared them to tape, and there were the same timecode discrapancies. But we did an online test with these clips anyway and found that, despite the inaccuracy of the timecode on the offline clips, the conform yielded a sequence whose picture matched the original offline sequence perfectly.
We also noticed that our tapes don’t all follow the same frame duplication pattern. I assumed that on each tape, the D-frame would be duplicated (over timecodes ending with 3 and 4, and 8 and 9). But this is not the case, it seems that the duplicated frames happen over different digits on each tape.
So my question is whether there is a way of dealing with this format in capture to ensure 100% frame accurate timecode all the time, or if these 1-frame discrepancies between offline clips and the master tapes are just par for the course with DVCPRO HD 720p24?
Also, let’s say there IS one frame that we are supposed to start capturing on, like ones ending in “00”. Since we will be generating an EDL with fixed handle lenght for the conform, won’t we just be reintroducing the timecode discrepancies, as our cutpoints of course will not always land on frames with timecode ending in “00”?
We are going to be reconform the show to HDCAM from the DVCPRO masters at a post facility. (This is a choice made by production that I have no say in, so avoiding making an EDL and just outputting directly from FCP is not an option.)
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5 Replies
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Ok, update on the above:
I found the reason for a) the difference in frame-duplication patterns between tapes and b) the reason why clips captured on the “00” frame yielded inaccurate timecode but still accurate conforms.
The reason is that in comparing offline clip timecode to the timecode on the tapes, I would open up the clip in the Viewer and scrub through the tape in the Log & Capture Window and do a frame-by-frame comparison. But it seems that the Log & Capture Window when connected through SDI (along with my NTSC monitor) have trouble dealing with the 24p format and preview what appear to be duplicate frames in places where they shouldn’t be. However, the Log & Capture Window connected via FireWire to the deck seems to preview the progressive frames just fine. So when using this configuration to scrub through tapes, all tapes seem to a) have the same frame-duplication pattern (the D frame repeated over frames ending in 3 & 4, and 8 & 9), and b) the clips that we captured starting on the “00” frame have 100% frame accurate timecode to what is on the tape.
So it would appear that capturing starting on the “00” frames is the way to go. But I have yet to test how an EDL/conform is affected by this necessity…
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Julian
a couple of things I want to comment on.
1) 720p24 is always NonDrop. (all 24p content is)
2) That BMD card cannot play out 720p24- it does not exist as a video out format over HDSHD or Component- while I can set my Kona cards to play out 720p24 no HD monitor accepts it, it only is used for a realtime conversion from 720p24 to 1080 24sf.
3) sounds as if you are allowing the FCP to determine the pulldown – DO NOT- FCP always defaults to a 2:2:2:4 cadence if not told to do otherwise. On the Kona cards I can set the cadence of the redundant frames to my choice of pattern
” However, the Log & Capture Window connected via FireWire to the deck seems to preview the progressive frames just fine.”
thats because FW is a Data protocol and not video.
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows -
[gary adcock] “3) sounds as if you are allowing the FCP to determine the pulldown – DO NOT- FCP always defaults to a 2:2:2:4 cadence if not told to do otherwise. On the Kona cards I can set the cadence of the redundant frames to my choice of pattern”
Thanks for your response. I don’t think the decklink has options for changing the cadence. I am using the 720P 24 easy setup that installed in FCP when I installead the Decklink’s drivers. I’d be surprised if its a cadence issue, because the 23.98 clip that is captured has 24 good frames, with no dupe frames, so it appears to be extracting the duplicate frames correctly. FCP has been set to 2:3:2:2 but I think this just effects playback to the monitor, not capture.
The problem is the timecode, If a clip is captured or an EDL is generated that contains in- points on a D frame, then my timecode goes out….
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Well it appears like capturing native through firewire eleminates this issue. Its a sad day, when firewire appears more reliable than your capture card. Interestingly the decklink deals with soure timecode in a 30 time base, while firewire has 60 based timecode. Not sure if this is relevant to anything. Nor how it will effect relinking my timeline.
Anyways, I’m going to dig a few tapes this way and do some more tests. If anyone has any suggestions as to what will make the decklink digitize this material 100% accurately I’m all ears.
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[Julian Clarke] “. I am using the 720P 24 easy setup that installed in FCP when I installead the Decklink’s drivers. I’d be surprised if its a cadence issue, because the 23.98 clip that is captured has 24 good frames, with no dupe frames, so it appears to be extracting the duplicate frames correctly.”
But capture was not your issue, playback was, and that was what I was referring to. The BMD card is not giving you the proper pulldown cadence when playing back the 24 in the 60p video stream, this is an ongoing issue with the BMD cards, relying on FCP to handle what should be on the card pref settings.
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows
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