Video Formats

The choice of video format is actually limited by your choice of media type. So, it is important to know what video format each media type supports. The table on the right shows you the available video format choices for each media type.

As you can see, with the exception of MiniDV camcorders, all other camcorders record their files in MPEG-2 for standard definition videos and AVCHD for high definition videos. MiniDV camcorders record in the DV format in standard definition and the HDV format in high definition. Let's take a look at the advantages and disadvantages of each video format.

Standard Definition Formats

Camcorders that support random access media like hard drives, flash media and DVD use MPEG-2 compression, the same compression used in DVD movies. Therefore, they are constrained by a total bitrate limit (video + audio) of 10.08 Mbits/s.

The video bit rate itself is limited to 9 Mbits/s with the remaining allocated to the audio. The audio in MPEG-2 video can be recorded in a variety of formats but they generally allow up to 6 channels of audio.

Most MPEG-2 camcorders support the maximum DVD bit rate of 9 Mbits/s, so you can literally create your own DVD movies. You can also set them to use lower bit rates, essentially compressing them at a higher level, for a longer recording time. However, video quality drops as the bit rate drops. You get more compression artifacts as you lower the bit rate.

DV camcorders do not use MPEG-2 compression, unlike what some sales people may tell you. They deliver DVD-quality video, but use DCT video compression with a bit rate of 25 Mbits/s. Audio is encoded as two 16-bit channels at 48 kHz or four 12-bit channels at 32 kHz. However, most users generally stick with just two stereo channels at 48 kHz for the best audio quality possible.

DV video quality is better than MPEG-2 video even at the same bit rate because it only does intraframe compression, while MPEG-2 also performs interframe (temporal) compression. In other words, DV only compresses each individual frame, while MPEG-2 compresses the video across several frames, removing similar data in multiple frames.

In addition, DV video has a much higher bit rate of 25 Mbits/s than DVD-quality MPEG-2. As such. DV camcorders delivers much better video quality than MPEG-2 camcorders. The use of intraframe compression only also allows for easy editing by video-editing software. That's why it's the format used in professional camcorders.

However, DV's audio support is limited to just two high-quality audio channels, or four lower-quality audio channels. MPEG-2, on the other hand, supports a wide variety of audio formats with up to 6 audio channels. Of course, the actual recorded format varies from camcorder to camcorder. Many MPEG-2 camcorders record in 16-bit stereo (two audio channels) although some newer camcorders like the Sony HDR-SR1 and the Panasonic HDC-SD1 can record in Dolby Digital 5.1 channels.

High Definition Formats

HD camcorders that support random access media like hard drives, flash media and DVD use AVCHD compression. This is based on the MPEG-4 AVC (H.264) video compression with a maximum bit rate of 24 Mbits/s. However, most camcorders record at much lower bit rates, usually 15 Mbits/s or less.

The audio in AVCHD is recorded as either uncompressed linear PCM or compressed AC-3 format with up to 7.1 channels. Most HD camcorders recorded in two 16-bit stereo channels, although some camcorders like the Sony HDR-SR1 and the Panasonic HDC-SD1 can record in Dolby Digital 5.1 channels.

HDV is the high definition version of the DV format. It uses MPEG-2 compression which is more efficient than the DV compression since it also does interframe compression (instead of just intraframe compression). This allows HDV camcorders to record higher resolution video with the same bit rates as standard DV video, albeit with the same motion artifacts and editing problems affecting MPEG-2 camcorders.

Audio support in HDV is limited to just two 16-bit audio channels at 48 kHz. The four 12-bit channel @ 32 kHz option in DV is not available and not likely to be missed. The audio is compressed in the MPEG-1 Layer 2 format at 384 kbits/s. HDV's audio quality is therefore technically poorer than DV which stores the audio uncompressed at 1536 kbits/s. However, the audio should be perceptually similar, like what MP3 audio is to CD audio.

Even with the higher compression, HDV video is definitely better than DV, due to the much higher resolution. Generally, HDV outperforms AVCHD in video quality although AVCHD has the potential to come close at its maximum bit rate. However, that doesn't seem to be possible at this time as practically all camcorders using the AVCHD format limit the bit rate to 15 Mbits/s or less.

On the other hand, audio support and quality is better with AVCHD. It allows for multiple audio channels and even uncompressed audio for maximum sound quality. However, the actual audio encoding supported by each camcorder varies. As mentioned above, most HD camcorders only record in two 16-bit channels even though the AVCHD format can support more.

AVCHD also has another advantage over HDV - any AVCHD video clip can be written to a DVD that can be directly played on a drive or player that supports AVCHD. Currently, that's limited to Blu-ray disc players, including the PlayStation 3 so this advantage may not be significant right now.

Although both HDV and AVCHD formats perform interframe compression which complicates video editing, industry support for HDV is far greater than AVCHD. Most video-editing software support HDV editing, while only a select few support AVCHD at present. AVCHD support is expected to improve over time but at this time, it's easier to edit HDV videos than AVCHD videos.