HDV on an iMac G5
Written by Johnny Chung Lee
Introduction - About HDV and HDTV - HDV and iMovieHD Ė Exporting Back to HDV tape Ė HDV and Final Cut Pro HD Ė Impressions of the HDR-FX1
Well, I guess itís really a $5000 question since thatís how much all the equipment cost. Like many others, I was very excited by the release of this camera and was waiting on the edge of my seat for Apple to officially announce native HDV support in their video applications. I was in the market for both a new camera and a new Mac, and my finances happen to be inline for acquiring both. But because I am not a video professional (most of my income does not come from doing video related work), I couldnít justify splurging on a Dual 2.5Ghz G5 with a matching flat panel.
Before I talk about using the HDR-FX1 with the iMac G5, I feel that itís important to cover exactly what HDV is and its relationship to the HDTV.
HDV stands for ďHigh-Definition Digital VideoĒ and
specifically refers to the specification for recording high-definition
resolution video onto the common mini DV (Digital Video) cassette tape. This specification was officially announced
However, it is important to understand that HDV is NOT the same as HDTV broadcast. The charts below compare the two specifications:
HDV Format Specifications
ATSC Format Specifications
Of particular relevance to the HDR-FX1 are the pixel dimensions of 1080i video in the HDV and the ATSC specifications. HDV provides only 1440 horizontal pixels while the more familiar ATSC specification has 1920 pixels. The HDV format uses a 4:3 aspect ratio image to store 16:9 anamorphic video when using 1080i. When transmitted to a HDTV television, the image is appropriately stretched to undo the horizontal squeezing during recording. This will be more important when talking about working with HDV video on the Mac later. Itís also worth noting the HDR-FX1 doesnít have 1440 pixel wide sensors, but only 960 pixel wide sensors. They use a technology called ďPixel ShiftĒ to tease a higher resolution out of fewer sensors. You can find more info about that on Google.
Also of great relevance when talking about editing HDV content is the MPEG2 encoding, a video compression technology that utilizes similarity in adjacent video frames to reduce the overall needed data rate. This is good for packing high-quality video into a small space, but it not very good for editing. Since the compression technique operates on groups of pictures, when you change one frame you have to recompress the other images that depended on it. This is going to play a big role in working with HDV images for editting. Standard DV and DVCPRO-HD do not use cross-frame compression and each frame can be manipulated independently from adjacent frames.
Okay enough techno-talk. What happens when you plug in the FX1 into an iMac running iMovie HD?
If you open the captured video in Quicktime Player, you can get more info about the captured video. There are a couple of interesting things to notice. First on the left, you can see that the data rate is 12.8MB/sec. This is substantially higher than the 3.2MB/sec used for standard DV, even though HDV is supposed to use the same 25Mbits/sec data rate and uses the same tapes. This due to the decompression step described above as you can see in the screenshot on the right. The native resolution of the video footage is 1440x1080 and format is the ďApple Intermediate CodecĒ used for editing. When you play it back, it will display at 1920x1080 stretching the pixels. However, the 17Ē iMac only has a 1440x900 display, so it will have to be viewed at less than 100%. Similar to DV, Quicktime will use low-fidelity fidelity playback for viewing HD video. It also worth noting that I only got 15-20fps during playback.
Editing HD content on an iMac G5 was very similar to the early days of editing DV. Response is reasonable but a little sluggish sometimes. Just doing cuts is very easy and effects donít really work in real-time. In fact, the preview window in my iMovie was partially garbled. Their HDV support still seems to be a little buggy. Working with HD content on an iMac may make you yearn for a faster computer, but it is certainly passable and eventually gets the job because many tasks (including import and export to tape) can be done as non-real time steps. As long as you are patient, it works.
Something that is not very well advertised either on Appleís of the HDV info websites is that exporting back to tape is a very computationally intensive task since it requires recompressing the video from the intermediate codec back into HDV compatible MPEG2. Even on the current fastest Mac (a dual 2.5 Ghz G5), it is 1/3rd to 1/5th real time to recompress the video (for every 1 minute of footage it takes 3-5 minutes to recompress) plus the time it takes to actually record to tape which is 1x real time. On the iMac 1.8GHz G5, exporting ran about 1/12th to 1/15th real time. So, a 5 minute short film would take about an hour and half to finally get it onto tape. Fortunately, this is an entirely hands-off process after you set it starting. You could set it to go when you go to sleep, and when you wake up, itís ready to go. I did have some strange errors with the time code and video stuttering when trying to print to tape artificially generated video, such as a leading black screen. This may have been because iMovie was trying to render the black screen in real time out to the camera. The stuttering went away when I used actual HDV footage to cap the ends my test movie. I attribute this bad behavior to a slightly buggy implementation/integration of their HDV codec with iMovie HD. I am sure this will get fixed quickly.
Though, in practice, it is not likely that you would be interested in going back to tape very often since nobody but yourself (or those individuals who are fortunate enough to also have an FX-1) can watch it. And trying to watch HD from your camcorder can be a little awkward, not to mention it induces more wear and tear on to your camera. Unfortunately, there is no readily available delivery mechanism through which consumers can share or distribute HD content yet. So, the only way to watch the material is either on your computer or by printing it back to tape and watching it on an HDTV capable television. Rendering out back to tape can be a pain, and the video formats and computers capable of viewing 1080i video in full glory are still slightly out of reach for most. Consumer HD technology is still a bit immature and although you can now shoot and edit HD. Watching and sharing HD conveniently is still about a year or more away when high-definition DVD recorders such as Blue-Ray or HD-DVD arrive. Quicktime 7 and H.264 (as well as WMA-HD) are the computer based offerings for viewing and exchanging high definition video. But to view high-definition material at 100% still requires a very high end computer by todayís standards as well as a 1920x1080 capable monitor which are also rare. In my opinion, itís probably best to shoot in HDV but edit in standard definition DV with a DVD target for now. The FX-1 provides real-time down conversion of HDV content to DV over firewire which looks surprisingly good over component video output compared to true 1080i material. More detail about this later in this write-up.
If you must go back to tape, you should be aware that you are taking another generation hit by recompressing it back into HDV compatible MPEG2. Simply taking the video off tape and then putting back onto tape requires 2 recompression generations beyond the compression done at the initial record time. In the few tests I ran of just taking footage off tape and then back on with no effects, there were occasional block artifacts that would appear in moving objects with very noisy/detail textures such as the hairs on my cat. They did not occur very frequently, but enough to be an issue with those obsessed with image quality. Though I would consider myself partially in the category, the fact that I will not likely be going back to tape very often (especially not for a final target) makes this much less of an issue for me.
iMovie HD leaves quite a lot to be desired by those familiar with a more sophisticated editing environment such as Final Cut Pro. However, Apple has not yet announced native HDV support in Final Cut Pro and Final Cut Express HD isn't due, from what I gather, until February 15th. Though soon, Final Cut Express is a crippled version of Final Cut Pro. So, it is still not incredibly helpful. However, it is possible to use iMovie HD as an HDV capture tool and edit HDV material in Final Cut Pro HD today.
When you capture footage in iMovie, it saves decoded the footage as Quicktime files inside your iMovie project package. Simply control-click/right-click your project package and choose ďShow Package ContentsĒ. Your captured footage is in the Media folder. Drag those clips out to a place accessible by other applications.
Open the footage files in Quicktime Player and open the Get Info panel. Select the video channel and go to Size. Though the video is only 1440x1080, the descriptor data says it should be played back at 1920x1080. This is going to be problematic when importing the clips into Final Cut because it is going to try and re-render the clips at 1920x1080. So, you have to manually adjust the playback size of these clips to be 1440x1080. This doesnít do anything to the actual video data, just changes the header information.
Now, create a new Sequence in Final Cut Pro HD with following settings:
When iMovie HD is installed, the Apple Intermediate Codec becomes available to all Quicktime applications.
When you import your footage, make sure to set those to also be Anamorphic 16:9. After you do that, you can then drag your clips into the timeline and they will play perfectly without having to render them. Effects can also be done in real-time with RT Extreme. However on the iMac, the real-time effects stutter severely and generally need to be rendered before viewing (just like the early days of DV). But itís relatively quick and not too much trouble. Scrubbing is also reasonably fast on an iMac G5.
Once you are done editing, you can then export your final movie to Quicktime using the Apple Intermediate Codec. Then you can take it back into iMovie to export to your camera or go to DVD.
Iím guessing the reason why they havenít yet released native HDV support in Final Cut Pro may concern some of the buggy behavior Iíve observed in their HDV decoder implementation and better integration with FCPs logging and batch capture tools. They may also be trying to tune performance of the decoder or even offer uncompressed editing support (though not likely). I donít know. But, I am pretty impressed with working with HDV material in Final Cut Pro HD on my little iMac thus far. I can only assume that their delays for supporting HDV in FCP HD are for a good reason and that they are only striving to make it that much better.
Working with HDV material isnít as smooth or fast as standard DV, but thatís to be expected. For light duty HDV work, the iMac does indeed work. You just wonít be able to take advantage of the real-time features that standard DV allows. So for now, it is for the brave, tolerant, and patient. But in another two years with substantially faster computers and readily available high-definition video DVD burners and players, working with HD content should be a breeze.Other Articles You May Find Interesting: DIY $14 Steadycam
Added: August 1, 2007
Written by Johnny Chung Lee on