Nikon D3100 Video Recording

Nikon pioneered video capability in its D90 digital SLR, and it's rapidly become a must-have feature, with essentially all the major manufacturers now providing some form of video capture in their DSLRs. Positioned as an affordable model near the entry level, the Nikon D3100 forgoes some of the more sophisticated features found in the video modes of enthusiast and professional digital SLRs, but it breaks new ground for Nikon in a couple of important areas. For the first time in a Nikon digital SLR, the D3100 can offer live autofocus during video recording. It also offers Full HD (aka 1080p) high definition video capture, ensuring that D3100 videos will look their best even on the latest high-def displays.

While it may not provide for external microphone connectivity, nor the level of exposure control demanded by pros and high-end video enthusiasts, the Nikon D3100 nonetheless includes an overall package of video features that will likely prove very compelling to the average consumer. Its genuinely useful live autofocus capability in particular will make it more appealing to the average user than most cameras, which rely solely on manual focus or single AF cycles during video capture.

Nikon D3100 Basic Video Specs

• 1080p (1,920 x 1,080) at 24 fps Full HD recording
• 720p (1,280 x 720) at 30 / 25 / 24 fps HD recording
• 640 x 424 at 24 fps SD recording
• MPEG-4 / H.264 AVC compression, .MOV container
• Full-time live autofocus is possible during recording, including tracking and face detection, albeit with actuation noise levels depending on the lens used
• Single-servo auto and manual focus also possible
• AF point position and size can be manually controlled
• Programmed-only exposure (that is, no true aperture-priority or shutter-priority)
• Exposure compensation and lock are available both before and during recording
• Picture control system provides creative options
• Monaural audio recording via built-in microphone
• Image stabilization during video capture, if offered by lens
  

Nikon D3100 Video: Image Size, Frame Rate, and Encoding

Nikon D3100 Video Resolutions & Recording Formats

The Nikon D3100 records a variety of resolutions and frame rates, using H.264 / MPEG-4 AVC compression, and storing the results in a .MOV container. At all resolutions, a frame rate of 23.976 frames per second is available, while for the 1,280 x 720 pixel frame rate only, there are also optional frame rates of 29.97 or 25 frames per second. No spec is provided for the sampling rate of the audio track during movie recording, though video players report monaural 16-bit PCM audio at 24 kHz, regardless of the video resolution and frame rate.

The table below shows the specs for various video recording options.

Nikon D3100 Video Options
H.264 / MPEG-4 AVC Compression (.MOV files)
Menu Designation	Resolution	Frame Rate	Card Capacity (very approximate)
1080 / 24	1,920 x 1,080 (16:9 aspect ratio)	23.976 fps	~2.3-2.5 MB/second (~14 minutes on 2GB card)
720 / 30	1,280 x 720 (16:9 aspect ratio)	29.97 fps	~1.3-1.5 MB/second (~24 minutes on 2GB card)
720 / 25	1,280 x 720 (16:9 aspect ratio)	25 fps	~1.3-1.5 MB/second (~24 minutes on 2GB card)
720 / 24	1,280 x 720 (16:9 aspect ratio)	23.976 fps	~1.0-1.2 MB/second (~30 minutes on 2GB card)
424 / 24	640 x 424 (3:2 aspect ratio)	23.976 fps	~0.5-0.6 MB/second (~60 minutes on 2GB card)

As noted above, the Nikon D3100 offers only one video recording format -- H.264 / MPEG-4 AVC, which is much more efficient in its use of memory card space than the older Motion JPEG format used by some competitors, but necessitates a more powerful, modern computer for playback and editing purposes. A choice of three frame rates -- approximately 24, 25, or 30 frames per second -- are possible when recording video with the Nikon D3100, but only when using the 720p (1,280 x 720 pixel) resolution mode. With the 1080p (Full HD, or 1,920 x 1,080 pixel) and non-standard 640 x 424 pixel video modes, movies are always recorded at approximately 24 frames per second. Due to the high data rates at Full HD resolution, Nikon cautions in the manual that it recommends use of at least a Class 6 SD memory card.

Here are some examples of video shot with our sample of the Nikon D3100:

Nikon D3100 Video Samples
1,920 x 1,080, 24 frames/second (42.1 MB)
1,280 x 720, 30 frames/second (22.0 MB)
640 x 424, 24 frames/second (9.1 MB)
Focus tracking example, ~24mm 1,920 x 1,080, 24 fps (39.2 MB) Decent AF tracking at 24mm, if not quite up to camcorder levels. (See AF tracking section below for details)	Focus tracking example, ~55mm 1,920 x 1,080, 24 fps (36.6 MB) Noisy but surprisingly good AF tracking at 55mm with the kit lens. (See AF tracking section below for details)
Autofocus slew, near/far 640x424, 24 fps (21.0 MB) The D3100 uses contrast-detect AF during video recording. It can track moving subjects decently well, but abrupt changes in focal distance can sometimes hang it up. Half-pressing the shutter button will force a broader AF "look," though, re-aquiring focus.	Autofocus noise with quieter lens (ultrasonic focus motor) 640x424, 24 fps (14.0 MB) The kit lens has an SWM motor (contrary to the commentary on this clip), but a bit higher-end model was a good bit quieter.
Indoor incandescent lighting (1,920 x 1,080 (19.1 MB) Moderately low light levels are no problem at all: good video quality here, under typical household (incandescent) lighting.	Rolling shutter ("Jello effect") (1,920 x 1,080, 24fps - 12.1 MB) (1,280 x 720, 30 fps - 8.2 MB) Less rolling shutter effect than many DSLRs we've tested. (Note relatively slight distortion in the thumbnail above, shot at 1080p/24 fps)

Nikon D3100 Video-Mode Focusing

The big news with the Nikon D3100's movie mode is that it provides live autofocus during video recording, a first for Nikon's DSLR lineup. Most DSLRs use what's called phase-detect autofocus for their still images. Phase-detect AF is very fast, but requires light to be directed onto a separate AF sensor via the reflex mirror, and so generally isn't available during video recording. The alternative is called contrast-detect AF, whereby the camera looks at the image to determine how sharp it is, makes a small adjustment in the focus setting, and then checks the sharpness again. Focus thus occurs in small steps, and is hence usually slower than with phase-detect systems.

Contrast-detect AF can be tweaked to be almost as fast as phase-detect, though, and that's what Nikon has managed with the D3100. It's perhaps not as fast as a phase-detect system could be, but as contrast-detect approaches go, it's reasonably quick, and probably fast enough for most consumer video applications.

The table below shows some examples of the Nikon D3100's autofocus tracking, with a very lively subject:

Nikon D3100: Tracking Autofocus (Crops below from clips shot with 18-55mm kit lens)
Frame 000: Shot at 55mm, the camera started out well-focused.
Frame 124: When Charlotte initially starts running, she "digs in" to launch herself. This dropped her head away from the middle of the frame, plus I'd started to tilt the camera up, to follow her run. Here, you can see the effect of the camera "seeing" the background; it's already shifted focus to the leaves and grass behind Charlotte.
Frame 128: It looks like the focus actually continued to hunt in the more-distant direction; nothing is actually super-sharp here, but details in the background seem a bit sharper.
Frame 139: Charlotte's a blur here because she's moving so fast. The focus point is actually about right for her.
Frame 153: I mentioned freeze-frame like this being like extreme pixel-peeping. One reason is that desirable motion blur when the subject is moving or the camera is panning looks horrible when frame-grabbed. The blurring here is caused by the slow shutter speed and rapid camera panning. If the shutter speed were short enough to make a crisp image here, though, the abrupt differences between frames would make the video look very choppy.
Frame 214: Charlotte's starting her run back; the camera is front-focused just a bit here.
Frame 243: A good bit closer, the camera is tracking pretty well. Softness in Charlotte is mostly motion and compression; leaves on the lawn in the same plane as her are fairly sharp.
Frame 253: Still quite good; the fetch-toy is pretty sharp. Charlotte's face is soft, but again, that's a combo of motion and the fact that movie compression tends to step on lower-contrast detail.
Frame 267: Too close, too quickly. The AF lost tracking a few frames before this one. It did pretty good to track as close as it did with a fast-moving doggie, though.
Frame 282: Pretty much caught up: Charlotte's face is a bit soft in this frame, but the hair on her shoulder is in pretty good focus. This is about 0.6 seconds after frame 267, shown just above.

In considering the crops above, keep in mind that looking at frame-by-frame 1:1 crops like this is the equivalent of extreme pixel-peeping with still images: In a movie with fast-breaking action like this, most people wouldn't notice a few frames' worth of missed focus. Ditto the detail levels; you actually want motion blur to provide smooth transitions between frames: Too-short shutter speeds produce very choppy-looking motion. (Also, in line with our comments below, note that 1:1 crops from even HD video frames just aren't as sharp as the equivalent still-camera image would be. You may note that none of the crops above look tack-sharp, but that's pretty typical of DSLR HD video frame grabs when viewed 1:1 like this - at least among cameras we've tested.)

While I could sometimes confuse the Nikon D3100's contrast-detect video autofocus by switching very abruptly from a foreground to background object, in normal operation, I was surprised by how well it generally tracked motion. There was a little of the "hunting" typical of contrast-detect systems, but most of the time, I found that focus tracking issues had more to do with what passed through the center of the frame, rather than any inherent difficulty in tracking the subject. That is, many situations that looked like mis-focusing were the result of my letting the subject get out of the center of the frame, or of there being enough background peeking through to give the camera a legitimately mixed message as to what I wanted it to focus on.

In my time shooting video with the Nikon D3100, I used a single central focus point almost exclusively: It's possible that a wider focus area wouldn't have been as prone to jumping to the background when the subject wandered. This is one area where phase-detect AF can have an advantage: If you're operating in multipoint AF mode with phase-detect, the fact that the camera can tell exactly how far out of focus various parts of the image are -- and in what direction -- means it can pick the AF points showing as closest to the camera as being the ones most likely to correspond to the subject. The Nikon D3100's contrast-detect may do better about being pulled off-focus by momentary flashes of the background when it's operating in its wide-area AF mode, but I didn't have a chance to experiment with that while I had it for video shooting. The key point here, though, is that the camera's video-mode AF did a surprisingly adequate job of keeping up with reasonable amounts of subject motion. It won't be able to hold focus on a runner sliding into home shot from the perspective of the catcher, but it'll probably do fine with typical non-sports subjects.

The D3100 provides both Single-servo and Full-time AF modes for live view and video capture, and as well as the Wide and Normal AF-area modes just mentioned, also provides both Face-priority and Subject-tracking AF-area modes, and the face detection function does continue to operate during video capture, continuously determining which is the dominant face in the scene, and following it as it moves around the frame. You can also manually adjust the AF point position both before or during movie capture, using the four-way controller. You wouldn't be able to do so quickly enough to follow a fast-moving subject around the frame manually with the AF point, but if your subject is static or moving relatively slowly, the ability to change the point position during a movie could be useful. Interestingly, you can also change the AF point size by turning the Mode dial before video capture, or during it if you don't mind the significant handling noise from the dial's stiff detent. It seems almost to be an accidental behaviour, but might nonetheless prove useful if you want to quickly change the point size without stopping the video. The Macro scene mode uses a smaller AF point size than other scene modes, and so simply switching to or from this mode will change the point size immediately, simultaneously resetting the AF point to the center position.

All in all, I think the Nikon D3100's video autofocus abilities are well-suited to the consumer audience the camera is intended for. It's not quite up to camcorder levels of performance, but is good enough that most consumers won't notice its few bobbles. The lens-motor noise on the audio track is another matter, though: With the 18-55mm kit lens, focus noise is very obtrusive, even though it's equipped with an SWM (Supersonic Wave Motor). Switching to higher-end SWM Nikon lens greatly reduces the problem, but a complete solution requires an external mic -- something the average consumer won't be likely to purchase or use, and nor does the D3100 offer an external microphone port with which to connect one.

If AF noise is an issue and you have plenty of light available, you can always drop back to using manual focusing, which is all that most DSLRs offer anyway. It'd be nice if the kit lens were quieter, for better audio tracks on recorded video, though. (We suspect it's more of an issue with internal slop in the lens mechanism than noise from the motor itself: In which case, it's likely an issue that a quieter-operating lens would just increase the cost of the kit to the point that it'd take it out of the entry-level price class.)

Nikon D3100 Video Exposure Control

While the Nikon D3100 lets you record movies directly from any of its still-image exposure modes, including aperture-priority, shutter-priority, and full manual exposure modes, the shutter speed, aperture, and ISO settings for video recording are always automatically controlled. Thus, while the controls might suggest full PASM (programmed, aperture-priority, shutter-priority, and full manual exposure) exposure control for videos, none of the modes gives you direct control over depth of field. You can, however, adjust the overall exposure both before and during exposure by holding down the D3100's top panel Exposure Compensation button and turning the Command dial on the rear panel, although the stiff detent on this will cause very noticeable handling noise if audio recording is enabled, and the change in brightness between exposure compensation steps will be clearly visible in the recorded video. Perhaps more useful is the ability to lock exposure during video recording, by holding down the AE-L / AF-L button (or with repeated presses of the button, if AE lock (hold) is enabled through the Setup menu.)

Providing a measure of creative control, the Nikon D3100 offers access to its Picture Control system for movie recording. Described in detail on the Exposure tab, this allows camera settings for sharpening, contrast, brightness, saturation, and hue to be adjusted, either automatically via presets, or manually via fine-tuning of the presets. The D3100 also allows movie recording from its Scene modes, although exposure variables from the scene modes don't seem to apply to movie capture, only AF variables (as mentioned previously).

Nikon D3100 Movie-Mode Image Stabilization

Nikon's image stabilization technology is lens-based, so IS availability, effectiveness and impact on the audio track will depend on the lens you're using. We felt that the kit lens's IS worked well, and had relatively little impact on the audio. We could hear it as a background hiss in quiet passages, even with the camera relatively steady, though, so when recording in quiet settings, you'll probably want to turn it off.

Nikon D3100 Video: Audio recording

Like many entry-level SLR/SLD cameras with video recording capability, the Nikon D3100 can only record audio via its internal, monaural microphone. Nikon doesn't publish specs for the D3100's audio recording capability, though video players report monaural 16-bit PCM audio at 24 kHz. Subjectively, audio recorded with the camera's internal mic seemed plenty clear, although we don't currently test frequency response or sensitivity. We did notice that there was some audible hiss in audio tracks recorded with the in-camera mic in quiet environments. Fortunately, we didn't hear any audible "breathing" from the auto-gain system adjusting sensitivity as sound levels got louder or softer.

As noted, the Nikon D3100 doesn't have any provision for manual audio level control. This isn't a particular strike against the D3100, though, as manual level control is a feature found on only a few digital SLRs, and those are well above the D3100's price range. To sidestep this limitation, many amateur videographers simply use a separate, inexpensive digital audio recorder to record a separate soundtrack, which they then synchronize with the audio from the camera in their editing software. Software synchronization of audio tracks gives essentially perfect alignment of the video and externally-recorded video with relatively little effort.

Nikon D3100 Movie Recording User Interface

The Nikon D3100 makes movie recording very easy, as you can initiate it at any time, regardless of the mode-dial setting: Simply flick the Live View switch to initiate the D3100's live view mode, and then press the Movie Record button, conveniently located at the center of the Live View switch, and the camera will start recording video. Video resolution, frame rate, and time remaining are available near the top right corner of the rear-panel LCD during capture, and you can change resolution and frame rate settings at any time via the information display, or in a Movie Settings menu accessed from page two of the Shooting menu. The result is a camera that feels like it was intended to shoot video from the start, unlike some DSLRs where movie recording seems to have been grafted on as an afterthought -- and that ease of access to video recording makes it rather more likely you'll find yourself using the video mode to grab spontaneous video clips.

We've generally favored use of the shutter button to start and end video recording, but found ourselves really liking the convenience of the D3100's dedicated record button. Having it on the rear panel within reach of your thumb makes it fairly quick to access, although it could be even more comfortable if it was located nearer the top of the panel. After a brief familiarization period, the arrangement is very intuitive as well -- a tap of the index finger to grab a still, and the thumb to start or stop video capture. If you're in Single-servo AF mode and want to trigger an AF cycle during video capture, you can half-press the shutter button with your index finger, and it's equally easy to lock exposure by slipping your thumb upwards and left a little to the AE-L / AF-L button. If you want to capture a still image while video capture is underway, you can fully depress the shutter button, but video capture will cease when you do so, and doesn't resume afterwards. There's also a fair delay between fully pressing the shutter button during movie capture, and the still image being captured, especially if Single-servo autofocus is enabled and your subject is moving. (Although you can quickly flick to manual focus before pressing the shutter button to prevent this delay, if you don't mind the handling noise being picked up by the D3100's internal microphone).

One thing that we definitely didn't like (and that we've complained about before, on other video-recording SLRs and SLDs, was that the image framing abruptly changes when switching from normal Live View to movie recording. The still-image aspect ratio (width to length ratio of the frame) is 3:2, while the video aspect ratio for all but the lowest-resolution mode uses the 16:9 aspect ratio that's the standard for high-def television. We frequently found ourselves lining up for a movie shot, only to discover that we'd lost the top and bottom of the subject once we pressed the movie-record button. We'd really like to see a Live View display option that clearly indicated the movie-mode recording area on the Live View screen, to make it easier to set up your shots before pressing the Record button.

On the positive side, the D3100 avoids another bugbear of video recording on certain SLRs and SLDs, in that it has relatively little lag when first initiating video capture. We've found that some cameras we've tested introduce a significant delay between your pressing the button to start or stop recording, and in a few cases exacerbate this by halting the live view feed until recording begins. This last issue can be particularly frustrating, because it makes it near-impossible to accurately follow and frame a moving subject from the first frame of the video. A few cameras also exhibit the rather bizarre behaviour of cutting off video recording at a point some time before the record button was pressed to stop capture. We're pleased to say the D3100 suffers no such problems, with recording starting and stopping near-immediately on pressing the Movie Record button, and only a very modest stutter in the live view feed as recording starts.

Setting adjustments in movie mode are made via an extremely abbreviated Movie Settings menu, accessed from the second page of the Shooting Menu. Here's a list of the options found on the Movie Settings Menu:

Movie Settings Menu Options:
Top-Level Selection	Second-Level	Notes
Quality	- 1080 / 24 (1,920 x 1,080; 24 fps) - 720 / 30 (1,280 x 720; 30 fps) - 720 / 25 (1,280 x 720; 25 fps) - 720 / 24 (1,280 x 720; 24 fps) - 424 / 24 (640 x 424; 24 fps)	Selects the resolution and frame rate at which movies should be captured.
Sound	- On - Off	Enables or disables audio recording during movie capture.

Nikon D3100 Video Quality and Artifacts

Video produced by the Nikon D3100 seemed pretty comparable to that turned out by other video-capable consumer DSLRs, including many selling at significantly higher prices. Don't pixel-peep frame grabs (as we do below) and expect to see images as crisp as 2-megapixel still shots, but the levels of sharpness and we saw were generally on par with those of other consumer DSLR cameras, and better than some. Its video output was also largely free of compression artifacts, although at 640 x 424 pixels, it did start to show a little blockiness in areas of fine detail.

Here are some examples of what we found in the Nikon D3100's movie files:

Nikon D3100 Video Quality Samples
1,920 x 1,080	1,920 x 1,080, fast panning
Cropped and viewed 1:1 like this, the D3100's video looks soft - but this is pretty typical (actually fairly detailed) for HD frames from a consumer DSLR.	When panning rapidly, with a lot of the scene changing from frame to frame, some video compression schemes produce unsightly artifacts. To its credit, the D3100 just delivers soft motion blur. The motion blur is actually a good thing, producing smoother-looking video in the face of fast action.
1,280 x 720	640 x 424
At 1,280 x 720, it's quite a bit sharper at the pixel level. Again, this is fairly typical of video from consumer-level DSLRs. (Personally, we tend to record at 720p resolution like this, for just this reason: Files are generally somewhat smaller, and the image about as crisp-looking when played back.)	Things get sharper still at 640x424, but some compression artifacts also creep in, which you can see here as the blockiness in the grass fronds behind Marti's face.

Overall, we felt that the Nikon D3100's video output was very much on par with its competition, including SLR and SLD models costing considerably more.

Rolling Shutter Artifacts

Nikon D3100: Rolling Shutter Artifacts
While it still showed some "Jello effect," the Nikon D3100's rolling shutter artifacts were noticeably less pronounced than those of most SLRs we've tested.

Essentially every video-capable digital SLR/SLD currently on the market exhibits motion-related distortions called rolling shutter artifacts. These are caused because the image data is captured and read off the chip sequentially by rows, rather being captured all at once. The effect on moving objects is similar to that of a focal plane shutter in an SLR, but more pronounced, because the video frame is read out much more slowly than the slit of a focal plane shutter moves across the sensor.

For a camera that scans video frames vertically (as do all that we're aware of), rolling shutter artifacts will be most noticeable for subjects that are moving rapidly side to side, or when the camera itself is being panned horizontally. Verticals in the scene will appear tilted to the right or left, depending on the direction of camera motion. As an example, consider the case of a camera being panned from left to right, with a flagpole or other vertical object in the middle of the scene when recording for a particular frame begins: If the top of the object was centered horizontally when the first line of the video frame is acquired, by the time the last line of the frame has been captured, the bottom of the object will have shifted to somewhere left of center: As a result, the vertical object would appear to be leaning to the right. When the camera is jiggled from side to side, your subjects will look like they're made of Jello, hence the popular term "Jello effect."

The frame rate of the Nikon D3100 suggests that this scanned readout would happen every 1/24th to 1/30th of a second. In practice, we suspect that the readout process is faster than the frame rate would indicate, because its Jello effect seemed much less pronounced than we're accustomed to among SLRs we've tested. This isn't any sort of a scientific result, but we felt that the D3100's video images were more stable than those of most SLRs on the market.

Computer Requirements for Viewing HD Video

A typical computer these days has little trouble dealing with still images, but high definition video can be another matter. Depending on the file format involved, it can take a pretty beefy computer to handle HD-resolution video playback without stuttering or dropping frames. The Nikon D3100 supports only the MPEG-4 / H.264 AVC recording format. While this is much more space-efficient on the memory card than the Motion JPEG format used by some cameras, and displays well on HD television sets, it's much harder for computers to decode. If most of your video playback will be on a computer, you may want to download our samples and confirm it's powerful enough to handle AVCHD playback and editing.

Nikon D3100 Video Mode: The Bottom Line

Overall, we felt that the Nikon D3100's video mode was a good step in the right direction, as most consumers will want their cameras to be able to focus during video recording. Video recording was pretty hassle-free, and it handled moderate and low light levels pretty well. Its exposure curve also seems biased towards slower shutter speed, which does a lot to avoid the choppy look of the video from many digital cameras when shooting under bright lighting. (Albeit at some cost in sharpness, due to the small lens apertures the camera will use in direct sunlight.)

The one notable fly in the ointment is the amount of noise the kit lens' focus motor produces in the audio tracks. Even though it uses an SWM (ultrasonic) focus motor, its noise was still objectionable. A higher-end SWM lens would likely fix the problem entirely, but would require an extra purchase, though, a step that the entry-level consumers that the D3100 is aimed at are unlikely to make. That said, it's surely better to have a camera that can focus during video, even at the cost of noise on the soundtrack than one that can't focus at all. (You can always switch to manual focus if the noise is an issue.)

Bottom line, the Nikon D3100 is a solid step forward for video capability in a feature-rich digital SLR at a very affordable price point.