Figure 4-42 The submenu for Video Parameters
The video functions of small cameras are often overlooked by photographers. We take photographs, not video clips, right? Well, with the CHDK activated you may change your mind.
Video sequences are quite memory-hungry. That is the reason why the camera compresses all video frames. Doing so saves a large amount of memory but also reduces quality. To support different requirements, the camera offers different video modes: 640 (640×480 pixels), 640 LP, and 320 (320×240 pixels). Compared to 640, the 640 LP mode generates only half the amount of data, so that the maximum length of a video sequence is doubled — albeit at a lower quality. The 320 mode produces only a third of the data, resulting in a tripled maximum length. Some cameras also offer a Compact mode (160×120 pixels for sending videos by email) that reduces the amount of data by around a factor of nine. Here, the clip length is restricted to three minutes.
Generally, the clip length is restricted to 4 GB or one hour, whichever is shorter. Some older cameras only allow for 1 GB, but the CHDK removes that limit. In addition, the CHDK allows you extended and fine-grained control over video quality and compression. You have the option (in menu entry Video Mode) to specify the quality, either in terms of compression (CBR mode, Constant Bitrate) or quality (VBR mode, Variable Bitrate). When the quality mode is used, the quality remains constant and the camera automatically adapts the bitrate to the quality setting and subject matter. A higher quality setting leads, of course, to a higher bitrate — and a subject with finer details as well.
- The Video Bitrate can be set to the values 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5 and 3.
- The Video Quality can be set to a value between 1 and 99, with 99 representing the best quality with the least compression. The camera’s native 640 mode is equivalent to a setting of 70-75.
So, you can in fact get a better quality than what the native video mode provides. In particular, close-ups and out-of-focus objects will look more natural. However, it may well be that the camera or the memory card is unable to handle such a large amount of data. In this case, the CHDK shows a warning sign (!) on the display. When the camera’s internal buffers overflow, the video sequence is aborted in a controlled manner.
Let’s discuss the other parameters:
- Clear Video Params on Start? Enable this entry if you want to reset the camera’s video facility to its native state on power-up.
- Fast Video Control? This allows you to pause the video recording with the LEFT button. You can then resume with the RIGHT button. Note: This does not work with all cameras.
- Video Quality Control? This allows you to change the video quality or bitrate DURING recording with the UP (increase) or DOWN (decrease) buttons. Again, this does not work with all cameras.
- Enable Optical Zoom. Many of the supported cameras do not allow the use of optical zoom during recording, but rather restrict the zoom to the range of the Digital Zoom. Digital Zoom is not a bad thing when recording video; it is silent, and the quality does not suffer much because the camera sensor has a much higher resolution than what is needed for video. Still, in combination with the Optical Zoom, you can get those long-range zooming shots. For instance, when the optical zoom range is 3 and the digital zoom range is 4, you would get a zoom range of 12. Unfortunately, for most cameras, the manufacturer has disabled the Optical Zoom during recording, probably to avoid complaints from customers who are irritated about the noise from the focus mechanism in the soundtrack. The CHDK allows you to lift that restriction and enjoy a wide zoom range. And the noise? Well, some editing of the soundtrack is required. Unfortunately, the Enable Optical Zoom function does not work on all cameras (it doesn’t on my SD1100, for example).
- Mute During Zooming. This entry is not present on all cameras. It allows you to mute the sound recording while zooming and thus avoid recording the noise generated by the focus mechanism.
- AF key. This entry is not present on all cameras. It allows assigning a key (shutter halfpress or FUNC/SET) to the autofocus function. Pressing this button during recording will cause an autofocus scan. For example, when you start your sequence at infinity and pan on a close subject, you can press this button and refocus on that subject.
- Show Remaining Videotime. This entry controls the OSD during video recording. You can hide the remaining recording time (Don’t), show it (hh:mm:ss), show the current bitrate in kilobytes per second (KB/s), or show both remaining time and bitrate.
- Refresh Rate (~sec). This entry controls how often the remaining video time is updated. Longer intervals result in more precise values; shorter intervals are more up-to-date.
Your camera’s native video options probably include an option for creating time-lapse movies. This feature is quite limited; on my SD1100 I can select between a one and a two-second interval. In section 5.7.1 we will discuss how to create advanced time-lapse movies with the help of the CHDK—in HD quality, of course.
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