HDV Post Production

Post production: HD for Indies is a fantastic blog by a fellow in Texas, Mike Curtis, who shares a vast amount of information on how HD can be used for low budget films. But by "low" he means the low millions or low hundreds of thousands. In this blog I want to concentrate on Low as in I'm doing this on the computer I also use to surf the net on and write emails, etc etc. More like "HD for Amateurs and Starving Artists". However I want something more flexible than iMovie and Final Cut Express.

I'll share my set up.

I still on FCP HD (4.5) so native HDV is out. Also, I'm on a G5 iMac (2Ghz, 20" screen, so I'm not THAT close to starving). I captured with Virtual-DVHS which worked correctly, but with no batch control, no preview while capturing, no cueing, and losing all timecode data on capture. I ended up with .m2t transport streams.

I then pulled these files into MPEG Streamclip to transcode to Quicktime. Streamclip now has a batch list which makes things easier, and two hours of footage took about all night to convert to DVCproHD 1080i.

We began editing the project in DVCproHD as it seemed the most suitable intermediate codec for use. We got nice realtime playback (but not effects, as FCP4.5 does not support the iMac's PCI-e graphics card) but the footage was noticeably softer, and there had been quite a colour shift from the original MPEG streams. I found the Apple intermediate Codec didn't play well in my FCP 4.5 (this may again because of FCP expecting an AGP card). Graeme Nattress (of Nattress filters for FCP/Final Touch fame) recommended PhotoJPEG 75%. I've been a fan of PhotoJPEG for a while when I found that for offline quality work it offered the best balance of quality, file size and playback. Even on fairly low power kit (and this was back in 2001 when I was editing on a G3 ibook) you could get good looking playback on offline files. So it's been nice to find out that it scales up well to being a suitable offline intermediate for HD. While there was a slight shift from the MPEG to PhotoJPEG, it was in a more pleasing direction (colours were more saturated, contrast was a little stronger) and anyway I assumed I'd be going back to the MPEG files anyway.

Editing with PhotoJPEG was pretty good. Effects rendered fast, and we did the titles in JPEG too so they rendered REAL fast. However I found JPEG's Achilles heel, it doesn't work well for multi generation work. Some basic reframes (to cut out mics in the shot, visible lights, etc) and rig removal for some reflections and cables in shot threw up some fairly obvious shifts in tones and a much courser, grainier image quality. to combat this, I re-did the resizes in FCP rather than after effects and the wire removal I re-rendered, this time with effects in 8 bit uncompressed all the way through. It was much better.

Going back to the MPEG streams once the edit was done was a pain, as FCP wanted to find clips with .mov extensions, which meant I had to individually select every similarly named .m2v file (demuxed from the m2t files with MPEG streamclip).

They loaded slowly but accurately, however any attempt to render anything or export at all just crashed the program. I REALLY need to upgrade FCP, but that's not possible right now. So I decided to do everything at SD at this point, and I'll just have to keep the M2T files online until I can upgrade to FCP 6 (might as well skip 5 at this point.) I tried FCP5 on one of the computers at work, which was a 1.4Ghz G4 eMac, and while playback wasn't flawless, it was pretty good. It seemed to drop parts of the image rather than whole frames, but when the playback window was resized to fit the eMac screen it was barely noticeable. There was even some very basic realtime playback (frame droppy dissolve, one layer title or a bit of simple colour correction). In order to get back to HDV tape I rendered out a Apple Intermediate Codec Quicktime file which I dropped into an iMovie project, which then rendered out a HDV master to go back to tape. All in all it looks pretty good, but close examination reveals that there are have built up quite significant compression artefacts. With FCP5 this wouldn't be such a problem as you would go directly from HDV originals to your output codec of choice, though for me this would mean I would not be able to use FFmpegX to create DVD and H.264 files. FFmpegX seems to have issues with Quicktime movies, it really prefers to have MPEG files in some form. It created very high quality h.264 files at 1280x720 25p but naturally had to retain some of the compression artefacts from the MPEG2-AID-MPEG2 chain, before adding it's own effects. However it looks extremely good considering for a 9 minute movie the final file size is only 190MB.

One thing I'm having difficulty with at the moment is colour correction. SD uses the 601 colour space, HD the 702 colour space. I think there are problems in going from one to the other. When I'm transferring to DVD or DV tape, and playing back on TV, the image is far too bright, which causes sync problems when played back on TV.

More on colour correction later...