Digitizing Analog Video through a Digital Camcorder

This article explains a setup and workflow for digitizing analog video (e.g. VHS, Beta, Video 2000, LaserDisc, …) using a Mac and digital camcorder – in high quality and with interlacing intact; optimized for archival. We will use a old-school digital camcorder (they are cheap!) to convert the analog signal to a high-quality digital “DV” stream and then record the DV stream on a Mac using a FireWire connection.

The Problem with Interlaced Video

Standard definition analog video is either

• 576i50 (PAL/SECAM): 25 full frames per second of 720×576 pixels, interlaced
• 480i60 (NTSC): 30 full frames per second of 720×480 pixels, interlaced

Interlaced means that every full frame is split into two “fields”, one with the picture’s 288 (PAL; NTSC: 240) odd lines, and one with the 288 (240) even lines. These two fields can represent one moment in time: When combining them, they will give 25 (30) full 720×576 (720×480) frames. Or they can be recorded 1/50 (1/60) second apart, giving motion at a resolution of 50 (60) Hz, but at half the vertical resolution, and with the set of lines alternating every time.

Interlaced video was natural for old CRT displays, but in order to show interlaced video on modern displays or encode them into modern video compression formats, they need to be converted into progressive format, i.e. deinterlaced.

The two fields are always transmitted one after the other, and it is unclear whether every two fields should be combined (“comb filter”) for a 25 (30) Hz video or whether the 50 (60) fields should be vertically upscaled for a 50 (60) Hz video. Using the wrong method means either combing artifacts or flickering.

The worst part is when the pairing of fields is inconsistent, like in this example of Futurama or whenever two scenes are composited in the original SD version of Star Trek TNG.

So deinterlacing is hard, especially if you want to do it well. When digitizing analog video, it is best to keep the interlacing intact. When playing the file, VLC for instance will already do pretty good deinterlacing by default – and tomorrow’s VLC will certainly do a better job. And if you come back to the footage years later to share it or reuse parts in an HD video, you can use the best deinterlacer available then!

So all in all, if you want to archive analog video, you should keep it interlaced. Many simple solutions won’t do this, but this solution does.

Digital Video and DV

A full, uncompressed digital representation of a PAL signal is 50 times a second a 720×576 image at 24 bits per pixel, which is 25x720x576x24: almost 240 Mbits/sec.

This implies “4:4:4”, meaning every 2×2 pixels have four brightness values (Y’) and four values each for the two color components (Cb and Cr). Most digital formats use chroma subsampling, meaning that a 2×2 pixel grid has fewer chroma values. Since the human visual system is less sensitive to color than it is to brightness, 4:2:2 (half horizontal chroma resolution) is practically indistinguishable from 4:4:4.

The 1986 D-1 format uses 4:2:2 chroma subsampling and thus reduces the data rate by a factor of 1.5 to about 160 MBits/sec. Sony’s 1993 Digital Betacam additionally uses lossy compression to reduce the data rate by a factor of 2.34:1 down to about 70 MBits/sec. Both formats were meant for professional use.

The consumer format for digital SD camcorders is the 1994 DV (“Digital Video”). It uses 4:2:0 chroma subsampling (one color value per 2×2) for PAL and 4:1:1 (one color value per 4×1) for NTSC, which reduces 4:4:4 data by a factor of 2. The resulting data is lossily DCT-compressed by a factor of 5, leading to a data rate of 25 MBit/sec.

DV embeds an uncompressed 48 kHz 16 bit stereo PCM audio stream, which adds 1.5 MBit/sec (or alternatively, two 32 kHz 12 bit stereo streams with the same total bitrate).

Unlike today’s common compression methods (e.g. MPEG-2, H.264, H.265), DV compresses images individually, so in the stream, there are no dependencies between images. You can imagine DV as a stream of 64 KB JPEG images. This allows frame-exact editing and allows for simpler encoder and decoder hardware, but means that a higher data rate is required for the same quality. A 25 MBit/sec DV stream is roughly equivalent to a 10 MBit/sec MPEG-2 stream and a 3 MBit/sec H.264 stream.

DV is an excellent match as an intermediate digital representation or even as an archival format for pretty much all analog media, it even surpasses LaserDisc and matches DVD in luma and chroma resolution (PAL values; NTSC are similar):

Format	Luma	Chroma
VHS	320×576	40×288
Betamax	333×576	40×288
S-VHS	560×576	40×288
Broadcast	440×576	120×288
LaserDisc	560×576	120×288
DVD	720×576	360×288
DV	720×576	360×2881

DV’s DCT-based compression is lossy but quite gentle, and given the increased resolution of DV compared to all analog media, it will capture virtually all data from the analog media.

Digital SD Camcorders

There are two types of digital standard definition camcorders:

• MiniDV (1995) was the industry standard. It uses a proprietary cassette format.
• Digital8 (1999) by Sony re-uses the same tapes as the analog Hi8 format.

Both Digital8 and MiniDV camcorders store a DV stream on tape and all devices come with a 4-pin FireWire/IEEE-1394/i.LINK connector that allows losslessly copying the DV stream from the camcorder to a second device or to a computer, or copying a DV stream to the device.

In addition to an analog video output (for connecting it to a TV), many camcorders also have an analog composite or even S-Video input. Unless the firmware has this feature disabled to avoid the European tax on video recorders (check the manual!), these camcorders can record analog video from an external input, or output a live digitized DV stream over FireWire (“DAC”).

This is what we will be using, so the tape format of the camcorder does not matter, since we won’t be using tape.

Setup

You need

• a high quality player for your VHS, Beta, Video 2000, LaserDisc etc. media
• a composite or S-Video cable plus audio to connect the player to the camcorder¹
• a Digital8 or miniDV camcorder that supports digitizing external sources (“DAC” functionality).
• an Apple Mac with a FireWire or Thunderbolt port, so:
  • any iMac, Mac mini, Mac Studio, Mac Pro or MacBook Pro
  • MacBook Air since Mid 2011
  • MacBook up to (!) Mid 2009, except Aluminum 2008

Depending on what kind of Port your Mac has, you need the following cables and adapters:

Port on Mac	Cables	Images
FireWire 400 (1999-)	4-pin (DV) to 6-pin (FW 400)
FireWire 800 (2009-)	4-pin (DV) to 9-pin (FW 800)
Thunderbolt 1/2 (2011-)	4-pin (DV) to 9-pin (FW 800) Thunderbolt to FireWire adapter
Thunderbolt 3/4 (2016-)	4-pin (DV) to 9-pin (FW 800) Thunderbolt to FireWire adapter Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter

The older the Mac, the fewer adapters you will need, but the more hassle it will be installing the necessary software. The sweet spot seem to be late FireWire 800 Macs (model years 2011-2012) or Macs with Thunderbolt 1/2 (model years 2011-2015).

Installing Tools

macOS supports DV video over FireWire natively, so you can open QuickTime Player, and select “File -> New Movie Recording…” to preview what is being transmitted by the camcorder. While QuickTime Player can record, the resulting video will already be deinterlaced using the low-quality “blend” method.

Apple’s iMovie has a dedicated DV/FireWire import function that will save MOV-encapsulated DV video, but has the habit of silently stopping recording when there is an empty area of the source tape.

The open source ffmpeg tool not only allows grabbing the original DV bits from FireWire, it can also convert video in all kinds of formats.

If you are running macOS 11 (Big Sur) or later, install Homebrew, and then install ffmpeg with this Terminal command:

brew install ffmpeg

Homebrew should also work but is unsupported on 10.11 (El Capitan) through 10.15 (Catalina). If Homebrew does not work on your version of macOS, you may want to find an ffmpeg binary through other means or consider upgrading to a later version of macOS – maybe even through OpenCore Legacy Patcher.

Digitizing

Make sure the camcorder’s audio is configured to 48 KHz 16 bit mode (as opposed to 32 KHz 12 bit). Connect the camera to the Mac and switch it into “PLAY” or “DAC” mode. Then run the following Terminal command to list the available capture devices:

ffmpeg -f avfoundation -list_devices true -i ""

On my MacBook Pro, this prints:

AVFoundation video devices:
[0] DCR-TRV520E
[1] FaceTime HD Camera
[2] Capture screen 0
AVFoundation audio devices:
[0] Speaker Audio Recorder
[1] MacBook Pro Microphone

It detected the Sony DCR-TRV520E. We will have to pass this device name whenever we want to read DV data with ffmpeg.

To capture the video tape into a DV stream, enter the following command (replacing the device name) and press PLAY on the VCR immediately after.

ffmpeg -f avfoundation -capture_raw_data true -i "DCR-TRV520E" -c copy -map 0 -f rawvideo video.dv

Once the tape is finished, press Ctrl+C to stop recording. If you want to automatically stop the recording after a certain time, you can add something like -t 4:10:00 (4h 10m) to the command line.

You can monitor the progress by looking at the camcorder’s viewfinder or LCD, or by using this command in a different Terminal window:

tail -f video.dv | ffplay -i -

Compressing

While DV is an excellent archival format, it’s also big: about 11 GB per hour. MPEG-2 can slash this by a factor of three (4.5 GB per hour). The following line recompresses the DV into DVD-quality MPEG-2, leaving the interlacing intact.

ffmpeg -i video.dv -b:v 10M -flags +ildct+ilme video.vob

Here is the corresponding line to encode the video in H.264 at 3 MBit/sec, which is about the same quality, and also with interlacing intact. This will be a little more than 1 GB per hour – 10 times smaller than DV.

ffmpeg -i video.dv -b:v 3M -flags +ildct+ilme video.mp4

While H.265 has some basic support for interlaced video, neither ffmpeg nor VLC support it without tricks, and AV1 does not support interlaced video at all. Consequently, H.264 is effectively the latest compression format that you should use to store interlaced video.

On-the-fly Compression

Any Intel or Apple Silicon Mac can also encode MPEG-2 in real-time. The following line skips the intermediate DV file:

ffmpeg -f avfoundation -capture_raw_data true -i "DCR-TRV520E" -c copy -map 0 -f rawvideo pipe:1 | ffmpeg -i - -b:v 10M -flags +ildct+ilme video.vob

And this is the line to encode straight into H.264. You will need a 2015 or newer Mac for this, otherwise it won’t be able to keep up with the incoming data.

ffmpeg -f avfoundation -capture_raw_data true -i "DCR-TRV520E" -c copy -map 0 -f rawvideo pipe:1 | ffmpeg -i - -b:v 3M -flags +ildct+ilme video.mp4

Deinterlacing

If you need the video in progressive format, you can use the following commands to deinterlace the video. You should try the 50/60 Hz command first, which will retain motion smoothness. If the resulting video contains every frame twice (verify by single stepping with the arrow keys in QuickTime), the original material was 25/30 Hz, so you can to re-do the deinterlacing with a frame rate of 25/30.

MPEG-2, 10 MBit, 50/60 frames per second:

ffmpeg -i video.dv -vf yadif=1:-1:0 -b:v 10M video.vob

MPEG-2, 10 MBit, 25/30 frames per second:

ffmpeg -i video.dv -vf yadif=0:-1:0 -b:v 10M video.vob

H.264, 3 MBit, 50/60 frames per second:

ffmpeg -i video.dv -vf yadif=1:-1:0 -b:v 3M video.mp4

H.264, 3 MBit, 25/30 frames per second:

ffmpeg -i video.dv -vf yadif=0:-1:0 -b:v 3M video.mp4

H.265, 1.5 MBit, 50/60 frames per second:

ffmpeg -i video.dv -vf yadif=1:-1:0 -c:v libx265 -b:v 1.5M -tag:v hvc1 video.mp4

H.265, 1.5 MBit, 25/30 frames per second:

ffmpeg -i video.dv -vf yadif=0:-1:0 -c:v libx265 -b:v 1.5M -tag:v hvc1 video.mp4

While the YADIF filter in ffmpeg does a pretty good job, there are now also machine-learning based tool like Topaz Video AI for deinterlacing.

Remember though that you should archive the original interlaced data, since deinterlacing is lossy.

Limitations

This method only captures the 720×576 (720×480) video signal and one stereo audio track of your media. Depending on the media, there may be information that is not captured:

• PAL broadcast recordings usually contain teletext, albeit with lots of errors, because of the insufficient bandwidth of tape.
• NTSC broadcast recordings and pre-recorded media usually contain closed captioning.
• VHS contains a mono track and an optional HiFi stereo track. VHS players pick the HiFi stereo track if it exists, so this solution will not capture the mono track which, in theory, could contain entirely different audio.
• LaserDisc can contain digital audio (PCM, Dolby Digital or DTS). If you want to capture the audio losslessly, you need to record it in parallel using an S/PDIF connection.

In general, the recording will only be as good as the player can decode the media. If you don’t have access to a good player or if the media has defects, you may want to talk to a company that specializes in digitization services.

Simpler Solutions

If the solution described in this setup seems overkill, there are simpler solutions as well:

• A DVD recorder (or a VHS/DVD combo device like the Panasonic DMR-EX98V and DMR-EX99V) can convert analog sources (or VHS directly) into high-quality interlaced MPEG-2 files written to a recordable DVD. The downside is that these devices are usually limited to two (DVD-5), maybe four (DVD-9, i.e. dual-layer) hours of recording at 10 MBit/sec because of the limitied capacity of a DVD.

• There are devices that connect to the analog signal on one side and to a computer’s USB port on one side. The PC/Mac software will usually create a deinterlaced MP4 file.

• Technology Connections describes a solution where you connect the video player to an analog-to-HDMI box, and its output in turn to a device that records HDMI onto an SD card. This will also deinterlace the video.

Links

• Old Video Tapes Conversion via Thunderbolt / Firewire
• Capturing and Archiving MiniDV Tapes on macOS
• DVRescue
• HDTV subjective quality of H.264 vs. MPEG-2, with and without packet loss

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