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HDV over FireWire

Jan 1, 2005 12:00 PM, By Steve Mullen

The second in a two-part report examines methods of importing HDV material into FCP via FireWire.

Last month I described a procedure that will enable you to bring MPEG-2-based HD into an HD post suite equipped with AJA's Kona HD board. The procedure used an AJA HD10A (MSRP of $2,800) to convert a component analog signal from an HDV device to HD-SDI (SMPTE 292M). The 1.485Gbps or 1.485/1.001Gbps HD-SDI bit-stream was sent to a Kona HD using a 75Ω cable. (To get the complete Part 1 story, see “From Camera to Edit Suite” in the December issue.) In this article, I will discuss importing MPEG-2-based HDV video into Final Cut Pro via FireWire.

For last month's procedure, MPEG-2 source material was shot on 720p HDV using a JVC camcorder. The analog component signal came either from the camcorder or from a JVC HM-DH30000U D-VHS deck. The camcorder was able to directly output 720p60 video. However, by sending the camcorder's 720p29.97 signal to the D-VHS deck via an IEEE 1394 connection, I obtained both 720p59.94 and 1080i59.94 component analog output.

Stereo audio was sent via either an analog connection (from the camcorder) or an optical digital connection (from the HM-DH30000U deck) to Final Cut Pro. The optical connection obviously had the advantage of providing an all-digital signal path.

The HD video, however, followed a far more complex path. The camcorder decoded 720p HDV to base-band digital video, which was passed through three digital-to-analog converters within the camcorder and output to the HD10A. When the camcorder was set to “No Convert,” 720p60 video was output. When, however, “All To 1080i” was selected, the 1280×720 pixel video was upconverted to 1080i60 video.

In the former case, every frame was sent twice (1/60 second apart) to yield 60fps progressive video. In the latter case, odd and even lines were sent alternately as odd and even fields (1/60 second apart) to yield 60 fields-per-second interlaced video.

Once the analog video was input to the HD10A, it was passed through analog-to-digital converters to yield a base-band digital video signal. This signal was serialized for transmission over HD-SDI.

Since the JVC camcorders have — and most likely all future MPEG-2-based HD camcorders will have — an IEEE 1394 port, why not transfer both audio and video to Final Cut Pro using an all-digital path? To experiment with this path, AJA loaned me two of its products: a Kona HD board (MSRP of $3,995) and a HD10C2 (MSRP of $1,190). The tiny HD10C2 converts the HD-SDI bitstream from a Kona HD board to digital video that is passed through three digital-to-analog converters within the box. I connected the Kona HD board's single output BNC to the HD-SDI input BNC on the HD10C2 using a 75Ω cable. A large jack on the HD10C2 box accepted a supplied plug and cable that terminates in three BNC plugs. I then connected the three BNC plugs to my LCD projector so I could use it to view the Kona HD output.

My projector accepts 720p59.94, 720p60, 1080i59.94, and 1080i60. The Kona HD is slightly more limited, outputting only 720p59.94, 720p60, and 1080i59.94. The output frame rates of the Kona HD determine the rates of the material imported into Final Cut Pro. A standard 720p59.94 uncompressed Sequence would be the best match between the HDV camcorder and the ATSC world of 720p59.94 video. My goal, therefore, was to find a method that worked with such a Sequence.

For my one of my tests, as I recorded video I periodically used a clapboard to provide a way to check audio and video sync with frame accuracy. To perform the FireWire capture, I used Apple's DVHScap downloaded from http://developer.apple.com/sdk/FireWireX. I also downloaded MPEG Streamclip from www.alfanet.it/squared5/mpegstreamclip.html. Using Streamclip, you can select an in point and an out point for a file export. I selected a number of clips for export as QuickTime movies. During each export, Transport Stream video was demuxed, and the audio and video were combined into a movie. I chose the BlackMagic 8-bit codec from the list of codec options presented by Streamclip. (Of course, I could have chosen the BlackMagic 10-bit codec.) I set the frame rate to 29.97, as that was the frame rate of the source video.

After importing my movie clips into Final Cut Pro, I could play them in the Viewer. Unfortunately, as you might have already guessed, they would not play in either a 720p59.94 or a 720p60 Kona HD Sequence. That is because the clips' 29.97 frame rate matched neither type of Sequence.

I then tried two simple solutions to solve the frame-rate mismatch. For the first solution, I placed the clips into a Sequence and then used both Auto and Manual Render to convert the timeline video to 720p59.94. (See the dark purple column in the Table.) For the other solution, I batch-rendered all the clips from the BlackMagic codec at 29.97 to the BlackMagic codec at 59.94. (See the medium purple column in the Table.) The first solution resulted in a FCP “temp” file with a frame rate of 30fps. The latter solution resulted in a FCP “temp” file with a correct frame rate of 59.94, but with only one-half the correct duration. Therefore, only the first half of the clip played.

Frustrated, I tried another tack with Final Cut Pro. I went back to MPEG Streamclip and reselected the clips I wanted. Then I chose to demux each selection into an AIFF audio file and an MPEG-2 elementary video stream file. Now I imported the MPEG-2 video files into an FCP folder. When I looked at the picon of each imported video file, I saw that the file also included audio. That's because whenever two files have the same name, but one of the extensions is .m2v and the other is .aiff, the contents of the audio file are included automatically when the MPEG-2 video file is imported into Final Cut Pro.

Next, I batch-rendered the folder at 59.94fps to the BlackMagic 8-bit codec. During the render, the MPEG-2 video was decoded to uncompressed video, with each frame repeated, and the movie's frame rate set to 59.94fps. How long did this take? On a dual 2GHz G5, each source minute took about 10 minutes to render. When I placed these clips into a 720p59.94 Sequence, they played fine. (See the light purple column in the Table.) Finally, a working solution — although I don't think the process of selecting and exporting dozens, let alone hundreds, of clips using Streamclip would prove very efficient in actual production.

One solution is to “pre-edit” source clips into “selects reels” that carry the selected shots for a scene. (Or the takes to be used for a shot.) Pre-edit editing will become far more necessary with 1080i MPEG-2, because conversion times will double. That's why I've written HDVideoSplicer.

I opened two huge files in HDVideoSplicer that I had demuxed in Streamclip. Note that because no MPEG-2 decoding is done during demuxing, the process is very fast. (When opened, these movies automatically include both AIFF audio and MPEG-2 video.)

Then I opened several empty movies that would become my selects reels. Next, I selected the clips I wanted and copied and pasted them into the appropriate selects reels. When finished, I exported my selects reels using the BlackMagic 8-bit 720p codecs. (Again, I could have chosen the 10-bit codec.) Because HDVideoSplicer allows setting the export frame rate, I entered 59.94. During an export, MPEG-2 video is decoded to uncompressed video, and each frame is output as two frames. On a dual 2GHz G5, each minute of source video took about 12 minutes to export. After export, I imported my selects files into Final Cut Pro where they were ready for immediate playback in a 720p59.94 Kona HD Sequence. (See the white column in the Table.)

Once I had clips in Final Cut Pro Sequences, I checked for audio and video sync — as well as video quality. The Table above shows audio/video sync with a “+” indicating video leading audio.

To work with HDV from Sony's new HDR-FX1, you can use DVHScap to capture 1080i50 and 1080i60 HDV material and use MPEG Streamclip to demux it. HDVideoSplicer also works with both 1080i50 and 1080i60 material. Thus, the procedure should be the same for 1080i as it is for 720p. Since I had already created a sample of synthetic 1080i MPEG-2 with MPEG-1 Layer 2 audio, I put the sample though the final software procedure I've described. As expected, I had no problem playing selects reels in a 1080i59.94 Kona HD Sequence. Obviously, this is the correct uncompressed Sequence for HDV from the Sony.

These software procedures should also work with other types of MPEG-2-based HD. Both Blu-ray and blue-laser camcorders will certainly have both HD analog component and FireWire output. Moreover, there will be Blu-ray and blue-laser drives available for your computer. A computer can also directly read Panasonic P2 media. And, of course, P2 camcorders should have both HD analog component and FireWire output.

My experiments have convinced me that post houses that handle HDCAM and/or DVCPRO HD can easily and relatively cheaply also handle HD that is based on MPEG-2.

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