The $20 Mini DVR is garbage
Lately Youtube has become full of videos promoting MiniDVR as the digital recorder to shoot with tape-based camcorder without using tape, and even as the ultimate tool to digitize analog videos. Is it really that good? Let’s find out!
The MiniDVR combines a digitizer, recorder, battery and three buttons in one tiny package. It saves video to a MicroSD card having capacity up to 32 GB. The device does not have a screen. If it did, the whole thing would be larger and would drain the battery faster, so this seems like a sensible compromise.
Unknowingly, I’ve bought a DIY version. It came with two cables, each of them having a TRRS plug on one side, and wire leads on another. The ready-to-use variant should come with cables having plugs on both sides. This is not a big deal, I have a matching cable with RCA plugs. When buying a cable remember that the MiniDVR uses LRGV pin-out.
To set the recorder up, connect it to a monitor or a TV via composite output. The setup screen contains two pages. On the first page you select a recording format: “VGA”, “D1” or “HD”. You can choose whether to record audio, and whether to stop recording automatically in 10, 20 or 30 minutes. On the second page you can choose “light frequency” (no idea what it means, it can be 60 Hz or 50 Hz and does not seem to affect anything) and TV output format — NTSC or PAL.
After you’ve done with the config, connect the MiniDVR to a camcorder or another analog video source, turn it on, and use the “Left” button to start and stop recording.
“HD” mode
I’ve recorded several clips off TV. Presently, broadcast TV bitrates in the U.S. vary anywhere between 1/4 and 1/2 of what they used to be 20 years ago, yet thanks to improvements made to MPEG-2 codec the picture still passes as HD.
MiniDVR records with 1280×720 frame size in “HD” mode with triple the bitrate of broadcast TV, but it uses the outdated MJPEG codec, so picture quality suffers. The picture is full of color splotches and compression artifacts. Stairstepped diagonals indicate that the recorder uses half the lines at best. When recording from an interlaced feed, diagonals are broken, which means that the MiniDVR records only one field. Audio is clipped.
Maybe the “HD” mode can be used to capture DV video? Traditionally, DV camcorders use Firewire to send video digitally, some camcorders can use USB as well. If your camcorder cannot send full-resolution video over USB, and your computer has no Firewire port, then composite video becomes the last resort to get your video off a DV tape.
I decided to digitize a widescreen progressive-scan PAL DV video. The DV capture shows color streaks, probably caused by interlaced chroma in an otherwise progressive-scan video. This can be mitigated by blurring chroma vertically. The MiniDVR video shows stairstepping on diagonals and dot crawl.
“HD” mode of the MiniDVR is barely practical for digitizing standard definition content, and is completely unusable for HD.
“D1” mode
Sony created D1 digital format in the 1980s following the international Recommendation 601 as closely as possible. The variant corresponding to 625/50 TV standard has the frame size of 720x576, the 525/60 version has the frame size of 720x486. It uses 4:2:2 chrominance sampling and interlaced scanning. Video is recorded at 167 Mbit/s data rate.
The MiniDVR has the frame size in “D1” mode at 720x480 no matter whether the input is NTSC or PAL. For NTSC input, the MiniDVR correctly records at 29.97 fps, for PAL it records at 24.97 fps, not at exact 25 fps, which is bizarre. No matter the frame rate, the MiniDVR always uses progressive scanning at around 5-6 Mbit/s. Clearly, this “D1” pales in comparison to real D1.
I’ve recorded a couple of clips with my VHS camcorder: on tape, on the MiniDVR, and on the HD Capture Pro box, which I bought five years ago.
The MiniDVR video is noisier than VHS video recorded on tape, and compression artifacts can be seen even in a blurry and defocused scene. Because it drops every other field, the the video looks more jerky than from VHS capture.
The HD Capture box can record with SVGA resolution at 30 fps, with 720p resolution at 60 fps, and at 1080p resolution at 30 fps. To preserve all pictures, I used the 720p60 mode. The HD Capture box correctly converted interlaced video to progressive and recorded all the frames.
“D1” mode of the MiniDVR cannot faithfully capture interlaced video such as VHS, Video8 or DV.
I have not tested the “VGA” mode, it is similar to “D1”, but has 640x480 frame size and even lower bitrate of about 4 Mbit/s.
Performance analysis
There are many reasons for poor performance of the MiniDVR.
- It uses an ancient compression format, MJPEG, which needs plenty of bitrate. For example, DV video, which employs a modified variant of MJPEG, runs at 25 Mbit/s for standard definition, and 100 Mbit/s for high definition. The MiniDVR records at about 4 Mbit/s in VGA mode, 5–6 Mbit/s in D1 mode, and 12–15 Mbit/s in HD mode. Insufficient bitrate results in visible compression artifacts.
- The MiniDVR records half of the lines and half of the frames, so it loses both temporal and spatial resolution.
- It uses composite input, which is not meant for high definition video. In standard definition modes the picture does not look much better, because crosstalk between luminance and chrominance components of the video causes color fringing, rainbow, and dot crawl.
- It records Linear PCM digital audio at only 8 kHz sampling rate, this is so-called “telephone quality”. To make matters worse, the recording level is too high, and the audio constantly clips.
How MiniDVR can be improved
To make the MiniDVR usable for capturing analog video:
- it should employ a more efficient codec, even 30-year old MPEG-2 will work;
- it should record either native interlaced video, or should properly deinterlace it, converting each field into a complete frame;
- it should use correct frame rates for PAL video — 25/50 fps exactly, not some fractional number;
- it should use correct frame size for PAL: 720x576, not 720x480;
- it should use an effective comb filter to separate luminance and chrominance signals and prevent dot crawl;
- to record HD, the device must have an HDMI input;
- it should offer better sound quality, at the very least doubling sampling rate; using compressed audio like MP3 with lower bitrate will make more sense than linear PCM with 8 kHz sampling rate;
- audio should be recorded at a correct level, or should allow recording level adjustment.
Final thoughts
In its current form the MiniDVR cannot be used to capture video preserving its original quality. Video, recorded directly onto the MiniDVR bypassing tape looks worse than video, recorded on VHS tape, quite an achievement.
I suggest to use the device in “HD” mode and adjust aspect ratio if you shoot with an old-school 4:3 camcorder. This allows to squeeze the best quality out of it. Low frame rate cannot be helped, but many people cannot see the difference between, say, 30 and 60 fps, and of those who can, many prefer lower frame rate, because it offers more film-like less realistic look.
After all, if Super 8 is a thing at only 18 fps, why MiniDVR could not have its own look? Pixels on a screen are just a representation of reality, and if you like a particular flavor of it, who can judge your artistic vision. ■
