AVCHD is a format for the recording and playback of high definition video.
AVCHD is abbreviated for A dvanced V ideo C odec H igh D efinition.
The format has been jointly developed by Sony and Panasonic. In 2005, the two companies combined their efforts in creating a high definition format for tapeless consumer camcorders. Announced in 2006, the format allows recording high definition video onto 8cm DVD discs, SD/SDHC memory cards, "Memory Stick" cards and hard disk drives.
AVCHD has been designed to be compatible with Blu-ray Disc format and can be used for authoring and distribution of high definition video, though with reduced quality and interactivity compared to Blu-ray Disc.
The first AVCHD camcorder, Sony Handycam HDR-UX1, went on sale in September 2006.
AVCHD and its logo are trademarks of Panasonic corporation and Sony corporation.
Overview
AVCHD (AVC-HD, AVC HD) utilizes MPEG-4 AVC/H.264 (AVC) video compression codec and either Dolby AC-3 (Dolby Digital) or linear PCM audio compression codec. Uncompressed linear PCM audio is not supported in existing consumer devices, but is offered in the Sony NXCAM professional lineup.
Aside from recorded audio and video, AVCHD includes features to improve media presentation: menu navigation, slide shows and subtitles. The menu navigation system is similar to DVD-video, allowing access to individual videos from a common intro screen. Slide shows are prepared from a sequence of AVC still frames, and can be accompanied by a background audio track. Subtitles are used in some camcorders to timestamp the recordings.
Audio, video, subtitle, and ancillary streams are multiplexed into an MPEG transport stream and stored on media as binary files. Usually, memory cards and HDDs use the FAT32 file system, while optical discs employ UDF or ISO9660.
At the file system level, the structure of AVCHD is derived from the Blu-ray Disc specification, but is not identical to it. In particular, known Canon and Panasonic implementations use legacy "8.3" file naming convention, while Blu-ray discs utilize long filenames. Another difference is location of the BDMV directory, which contains media files. On a DVD-based camcorder the BDMV directory is placed at the root level, as on the Blu-ray disc. On the HDD-based Canon HG10 camcorder the BDMV directory is located in the AVCHD directory, which is placed at the root level. Solid-state Panasonic and Canon camcorders nest the AVCHD directory inside the PRIVATE directory. Following a standard agreed upon by many still camera manufacturers, solid-state camcorders have a root-level DCIM directory for still images.
AVCHD recordings can be transferred to a computer by connecting the camcorder via the USB connection. Many camcorders can record to removable media like SDHC and Memory Stick cards or DVD discs, which can be read on a computer directly. Copying files from an AVCHD camcorder or from removable media can be performed much faster than from a tape-based camcorder, because the transfer speed is not limited by realtime playback.
Just as editing HDV video once demanded an expensive high-end PC, the system requirements for AVCHD editing software currently limits it to powerful machines. Compared to HDV, AVCHD video compression requires 2-4x the processing power, placing a greater burden on the computer CPU and memory. Older computers, even those that are capable of handling HDV, are often unacceptably slow for editing AVCHD, and can even struggle with smooth playback of AVCHD recordings. Improvements in multi-core computing and graphics processor acceleration is bringing AVCHD playback to mainstream desktops and laptops.
Media
AVCHD specification allows using several kinds of recording media, in particular recordable DVD discs, memory cards, non-removable solid-state memory and hard disk drives. AVCHD camcorders do not use magnetic tape.
DVD disc
When AVCHD standard was first announced, it specified recordable DVD disc as the only recording medium. To reduce camcorder size, manufacturers opted for a 8 cm disc, sometimes called miniDVD. Recording capacity of a MiniDVD ranges from 1.4 GB for a single-sided single layer disc to 5.2 GB for a double-sided double layer disc.
Pros:
- DVDs are familiar to most consumers, thus considered user-friendly
- Recordable DVDs are relatively cheap
- Recorded disc can be played back in most Blu-ray players
- Discs can be used as immediate backup media, can be stored separately from a camcorder
Cons:
- The longevity of recordable DVDs is argued to be much shorter than expected
- Rewritable DVDs cost more than write-once discs
- DVDs have to be "finalized" to be played back on set-top players
- Double-layer recording is less robust than single-layer recording
- To use both sides of a double-sided disc it must be flipped over, because camcorders have pickup only from one side
- AVCHD DVDs cannot be played back on regular DVD players
- Recording data rate for DVD-based AVCHD camcorders is limited to 18 Mbit/s
- A single-sided single-layer 8 cm DVD can fit only 15 minutes of video at 12 Mbit/s data rate, 10 minutes at 18 Mbit/s data rate
- DVDs are very susceptible to vibration
- 8 cm DVDs cannot be used in most slot-loading drives and may even damage the drive
- Unlike HDDs and memory cards, the capacity of DVD discs has reached their limit
As capacity of memory cards grew while their price dropped, DVD discs quickly fell out of favor. All AVCHD camcorders released in 2008 and later use either built-in HDDs or solid-state memory as recording media.
While DVD discs are no longer used for initial acquisition, they are becoming popular as distribution media for playback on Blu-Ray disc players. A conventional single-layer 12 cm disc can fit up to 50 minutes of AVCHD video at 12 Mbit/s data rate. Many authoring programs offer an "AVCHD" profile for preparing high definition video and burning it on a DVD disc in a format compatible with most Blu-ray Disc players.
Hard disk drive
A hard disk drive was added as a possible medium to AVCHD specification shortly after the new video standard had been announced. Presently, capacity of HDDs ranges from 30 GB to 240 GB.
Pros:
- Higher capacity than other media types, which allows for longer continuous recording.
Cons:
- Sensitive to atmospheric pressure. Most HDD-based camcorders cannot be operated at altitudes above 10,000 feet (3,000 m).
- Vulnerable to mechanical shock or fast movement.
- All HDD-based AVCHD camcorders employ non-removable disks. To transfer video to a computer the camcorder must be connected with a USB cable. Most camcorders require using an AC power adapter for this operation.
- Despite that HDDs may have faster internal data transfer rate than DVDs and memory cards, the camcorder-to-computer transfer speed is limited by USB interface.
- Replacing a damaged HDD requires disassembling a camcorder and cannot be done by a consumer.
Solid-state memory card
Many tapeless camcorders record to memory cards, such as SD/SDHC cards or "Memory Stick" cards. Utilizing solid-state flash technology, memory cards offer rewritable storage in a compact form factor with no moving parts.
Many inexpensive memory cards are slower than HDDs, but are still fast enough to justify switching from tape-based to tapeless workflow. With transfer speeds ranging from 10 MByte/s to 20 Mbyte/s, it takes about 1 minute to transfer 1 GB of video. From practical standpoint, this means that one hour of video recorded at 17 Mbit/s data rate can be transferred onto a computer in about 8 minutes. For comparison, it takes one hour to capture one hour of HDV video.
Historically, flash memory capacity and pricing have improved steadily since introduction to the consumer market.
Panasonic chose removable flash memory as the only media for use in the company's professional AVCHD lineup, AVCCAM.
Pros:
- Compact and lightweight.
- Do not require time for spin-up and initialization, always ready for recording.
- Not vulnerable to magnetic fields.
- Can withstand a wider range of air pressure and humidity than HDDs.
- The camera is more likely to survive after being dropped than DVD, miniDV tape, and hard disk, which all have very delicate write/record head components.
- Can be easily backed up to DVD for viewing and for long-term archiving.
- Can store mixed media content, including still images (snapshot photos or still-frame captures).
- Most new computers, some TVs and Blu-ray Disc players, as well as many video players, per
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