Category Archives: Videos

CMOS versus CCD video imaging and the “Rolling Shutter” problem

Older video cameras used CCD-based image sensors. For various reasons, that I will explain in a moment, camera makers have largely switched to using CMOS-based image sensors on low end and even some low end semi-pro video cameras (like the Panasonic HMC-40). All of the new digital SLRs (DSLR) still cameras that also shoot video using high resolution CMOS sensors too.

But there’s a nasty problem with CMOS-based sensors that can cause the video image to resemble a shaky bowl of jello, as illustrated in this video comparison between the Canon HV20 (CMOS-based) and the Panasonic SD5 (CCD-based):

The problem is that the CMOS image sensor is read “line by line” from top to bottom.  If the image changes during the read out, then one line may be slightly offset or shifted from the previous line.  This is known as a “rolling shutter” and creates the peculiar “jello effect” since not all lines (or rows) in the image are lined up with all the others.

Old movie film cameras used a physical shutter that open and shut exposing an entire frame all at once. (Although, there are some issues with that too which we can ignore for now.)

CMOS reads the image row by row while CCDs read the entire image all at once and do not use a “rolling shutter” – hence, no jello on CCD cameras.

So why use CMOS instead of CCD? The basic reason is that CMOS uses less power and produces less heat and is less expensive. As image resolutions have increased, the size (and cost and power) of the CCD imager has gone up.

Camera makers, especially in the consumer market, are in an arms race to each have cameras featuring ever more pixels. This means most have switched to CMOS because, apparently, most consumers do not care about the jello or do not encounter it often enough.

In the DSLR world, most any camera with 10 or more megapixel resolution is CMOS. CMOS works great for most still photography. But when these DSLRs are used for video, they too suffer from awful “jello”.

There are other things to consider too – CCDs may show vertical streaks in photos when there are very bright lights (sun reflected on water, stage lights, etc) in the image.  For higher resolutions, CCDs need to be physically larger – and more expensive.

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Playing 1920×1080 MPEG4 video files without “stuttering”

I previously played my own HD videos (videos that I created) at 1920×1080 by streaming them off a slightly older Windows XP PC over a network to an Xbox 360 connected to an HDTV.

Two things happened that killed that solution:

  1. The Xbox 360 eventually died completely (already been down the “red ring of death” problem in the past).
  2. My youngest child is now old enough that she did not care if we replaced the 360.

Looking for a low cost solution I re-assigned my old 3.06 Ghz single processor machine still running XP to play videos through the VGA connector on the HDTV. I still used that machine for some software development but spent today transferring over the last files and programs I needed on to my much newer multi-core desktop that I use for development and video editing.

The good news is that this all went well.

The bad news is that any time I tried to play a 1920×1080 MPEG4 video (most of mine are encoded at 4 to 8 Mbps depending on the content), the images stuttered badly. One in particular looked like I was watching a slide show, not a video!

I tried using Quicktime, VLC and the Media Player Classic Home Cinema software and all had various kinds of problems from stuttering to false colors (VLC).

Looking around I discovered that the problem is due to H.264 decoders that are too slow and can not keep up with full frame video.

But there is a solution – CoreAVC 2.0 and CoreAAC codecs. They have optimized their H.264 decoders for far faster performance than all the others.

Once I bought and installed those codecs, I can now play the 1920×1080 H.264 videos in Windows Media Player and get smooth video. No frame drops that I could see. Plus, the fan on the PC only kicked up half way to keep the CPU cool – so the fan noise was lower too.

For the $18 cost of the software, I’ve replaced the parts of the Xbox 360 that we really wanted – streaming our own videos. Plus we can now watch YouTube, Hulu, Vimeo and eventually Netflix videos too. And I’m going to have give Flight Simulator or X-Plane a whirl soon too 🙂

The CoreAVC and AAC codecs are working well for me. You might take a look at them if you are having trouble playing 1920×1080 videos on an older computer.

Update: If you are having trouble playing 1920×1080 videos on Youtube … it is probably because your computer cannot keep up. Decoding and displaying an H.264 1920×1080 video image, at 30 times per second, seems to be beyond the capacity of most computers. My quad core computer seems to be able to just keep up. It might work better for you if you first wait for the entire video to download, and then try playing again. Alternatively, just use the 720p version. Most people cannot tell the difference between 1080p and 720p, especially after it was encoded once for upload to Youtube, and then transcoded at Youtube, downloaded and decoded to play on your computer.

How to shoot a parade video

Each year, Spokane, Wa holds an annual Lilac Festival and Armed Forces Day Parade. This is the largest evening Armed Forces Day Parade in the country, and one of the larger parades of any type on the west coast.

This year, 211 units participated in the parade, with 46 high school marching bands from throughout the state (and some from out of state). The parade typically has around 50 + or – bands. If you like marching bands, this is a neat parade!

Over the years, I have followed the West Valley High School Eagle Marching Band since my own kids previously went through that band program. While I no longer have any of my own kids in the band, I still run their web sites and some IT functions behind the scenes, and do some media work for them, all as a volunteer.

Video taping a marching band in a night time parade is difficult. If you stand on the curb and shoot video, the band goes by once and its all over with in 20 seconds.

The only solution is to march with the band. But that adds a lot of challenges, even more so at night. I cannot use auto exposure in the camera since the camera tries to add 36 db of gain to make the night time look like daylight and covering everything in awful noisy graininess. Similarly, audio levels can not use the ALC to adjust audio level automatically – that makes the entire band and crowd noise come across as loud mess.

The opening scene of the following video is shot near the TV coverage area. I set the gain to 0 db and shot at 1/60th of a second in 30p mode, Tv exposure mode, on the Canon XH A1. Once the band passes the TV lighting, I manually switch to 12 db gain and the XH A1 has sufficient aperture to automatically set the f-stop the rest of the parade.

Why not use 1/30th of a second rather than 1/60th, considering shooting at night? Two reasons. One, 1/30th of a second produces some blurring, but does enable using +6 db gain instead of +12 db gain. But the second reason is that motion stabilizing software (see below) does not work well with blurred images. Sharp images work much better and that requires at least the 1/60th of a second shutter speed (based on some experiments I did).

I also use both a short shot gun and the on camera mic during the parade. For the long shot at the beginning, I used the shot gun mic to cut down the crowd noise. But once I start moving with the band, I switch to the internal stereo mic to get better coverage (less directivity) of the sound pattern of the entire band.

At about 1 minute 35 seconds into the video, you’ll see my fake “Steadicam” in action. You’ll see this type of shot throughout the entire video.

How do I do this?
1. I use a monopod and attach a 3 pound weight to the bottom of the monopod. This creates a simple dynamic stabilizer. Imagine holding a stick with a weight at the bottom. As you move the stick around, gravity naturally pulls the weight back towards the center. The amount of weight and the length of the monopod influence the dampening effect. I use only a 3 pound weight because I have to carry the camera gear for several miles (the parade itself is 3 miles long, plus I usually walk 2 or 3 additional miles before and after the event).

2. Learn how to walk smoothly. Watch marching band performers – they “roll step” as they walk. This means rolling your feet in a smooth motion rather than stepping, greatly reducing your vertical motion. Surprisingly, you can learn to walk backwards for an even smoother effect which has to do with how your body mechanics works out. Add a slight crouch and slightly bent knees and with practice, this technique combined with the weighted monopod can product surprisingly smooth walking shots.

3. In post, use motion stabilizing software. There are several applications available today that do a good job of analyzing images for motion and then shift your images around to create the appearance of stability. Since they has the effect of adding black edges to your video after shifting, most also slightly enlarge your original video to eliminate the black edges. For this video, I just used the built in motion stabilizing feature in Apple’s iMovie 8. It took about 3 hours to analyze the HD video I had shot.

Even with motion stabilizing software, you will achieve the best results if you also use the tricks outlined in (1) and (2). You can see the effects of this fake “Steadicam” throughout the videos, but if you are in a hurry, you can see it in the first scene in Part 2, below.

Other tricks I use during the parade are to use the monopod for overhead shots, including walking shots. Sometimes I take a video clip standing in the midst of the band but did not do that this year. It would also be nice to take some low level shots from near ground level, but there is never enough time.

By the end of the parade, I am drenched in sweat and exhausted. In order to get many shots of both the front and back of the band, I have to shoot while the band marches by, then run back up to the front of the band.

This was shot using the Canon XH A1. I have shot daytime parades using an HV30, external BeachTek audio mixer, and a short shot gun XLR mic, plus wide angle lens (always go wide angle for these things). I use the XH A1 for the night parade because of its better light gathering capacity of the big lens and larger imagers. But it does weigh a bit more!

Part 1 of 2:

Part 2 of 2:

Download YouTube Videos as MP4 Files

Download YouTube Videos as MP4 Files.

The above is the new official way from Google/YouTube. Its in test mode now but accessible by following those instructions.

If you use Firefox, there are also many plug-ins available that can enable you to download .FLV and .MP4 video files from YouTube.

Recently, YouTube’s HD videos are downloadable as MP4 video files but only in non-HD modes suitable for use on an iPod. If you want the HD versions, you need to download the .FLV file and then probably convert to MP4.

To download the FLV files, use Download Helper. A type YouTube video will show several alternative downloads for the currently playing video.

One blogger, Rishabh Singla, attempted to determine what the different types mean and came up with the following table:

  1. Basic / Normal: FLV; 718 KB; 1x; Low
  2. HQ18: MP4; 1.4 MB; 2x; Medium
  3. HQ22: MP4; 4.5 MB; 6.4x; Very high
  4. HQ35: FLV; 2.7 MB; 3.9x; High
  5. HQ37: Container?; Size?; Factor?; Super

However, since the new Download feature has been added to YouTube, I do not believe that HQ44 is consistently an HD “very high” quality video, as shown. Some times it is, but sometimes, the FLV file option is much better.

When the FLV file is better, I download the FLV and either play it with VLC – or, I convert it to MP4. If you are using Windows, look for the free FLV to Zune file converter. If you play with the various options, you can do a very nice conversion to 1280×720 MP4 format. (I need to update this post later – I can not seem to find which FLV to Zune converter I have and where I got it from. Meanwhile, here is a different free converter – I have not tested.)