MPEG4 Camcorders - ASP vs. AVC, SD vs. HD
A couple of years ago the most advanced consumer camcorders could capture only standard definition video (SD) encoding it with MPEG4 ASP codec. So a "MPEG4 camcorder" at that time could do only one thing - record MPEG-4 ASP standard definition video (SD). Much has changed since that time. Some camcorders can now encode video with better MPEG4 AVC (H.264) codecs. There have appeared camcorders that can capture HD (High Definition) video. So it's not enough to just say a "MPEG4 camcorder" - you have to specify video resolution and codec.
So, camcorders can be divided into four groups:
- MPEG4 ASP SD
- MPEG4 ASP HD
- MPEG4 AVC SD
- MPEG4 AVC HD
This is not just a matter of different abbreviations, but also of common sense - you should pay close attention to it when you buy a camcorder.
Note that the most advanced MPEG4 AVC HD camcorder won't be the best choice for all users, even if we don't take its high price into account. So it's important to understand pros and cons of each camcorder type. Let's analyze this issue in more detail.
In order to determine which camcorder is your personal best choice, we'll try to answer another series of traditional questions: "What?", "Where?", "When?", and "How much?" Then we'll try to determine target audiences for each class of these camcorders.
"What?" Typical characteristics of camcorders of each group.
"Where?" Devices that can play video, captured by these camcorders.
"When?" Prospects of each camcorder.
"How much?" Your expenses on equipment and video playback.
But let's return to the theory at first.
MPEG-4 ASP and AVC - who is who?
In our previous articles we examined MPEG codecs with interframe compression, their differences from codecs where each frame is compressed - MJPEG and DV. So we'll not repeat ourselves. We'll focus on "interbreed" peculiarities of various MPEG-4 codecs.
MPEG-4 (ISO 14496) is a popular open standard developed by the Moving Picture Experts Group (MPEG), a workgroup of International Organization for Standardization (ISO). The MPEG-4 standard is divided into several substandards, in particular:
- ISO 14496-1, format of the MP4 file container
- ISO 14496-2 (Advanced Simple Profile - ASP)
- ISO 14496-3 (Advanced Audio Coding - AAC)
- ISO 14496-10 (Advanced Video Coding - AVC), it's also called H.264.
The MPEG-4 ASP group includes widely popular DivX and XviD codecs. MPEG-4 ASP has been used for a long time to record home video. It was so omnipresent that people omit "ASP" when they speak about it.
Consumer video devices have been using a MPEG-4 ASP profile called HTP (Home Theater Profile). As HTP was developed by authors of the DivX codec, it's often called DivX-certificate (do not confuse it with DivX codec).
HTP and DivX certificate are often associated with MPEG-4 ASP. But it's not correct - HTP does not include such video enhancements and bit rate reduction tools as:
- QPEL (Quarter Pixel Motion Search Precision)
- GMC (Global Motion Compensation)
- Besides, frame size in HTP is limited to 576 lines at 25 fps, or 480 lines at 30 fps.
That and similar names (DivX codec and DivX certificate) caused a great deal of terminology confusion here.
The MPEG-4 AVC substandard is one of the latest and most advanced video encoding formats. It has appeared relatively recently, only in 2003, as a result of cooperation between MPEG (Moving Pictures Experts Group) and VCEG (Video Coding Experts Group). This standard is called MPEG-4 Part 10 (AVC) by MPEG; VCEG calls it H.264 (by the number of the ITU document). Hence two names.
Just like MPEG-4 ASP, MPEG-4 AVC determines profiles:
- Baseline
- Main
- Extended
- Several High profiles
It's too early to say which profile will become more popular, because MPEG-4 AVC has been released only recently.
Unlike MPEG-4 ASP, MPEG-4 AVC offers more powerful tools to enhance video quality and reduce bit rates. In particular, they are CAVLC/CABAC lossless compression methods, variable block size (ASP block size is fixed), multiple reference frames, not just I/P/B-frames like in ASP RDO optimizations to decrease distortions, etc.
All these features help MPEG-4 AVC codecs consume bit rates much more efficiently, thus achieving higher video quality.
The reverse of the medal is higher requirements to MPEG-4 AVC video recording/playback devices.
For example, even an old 1 GHz Pentium-III or Celeron can cope with playing MPEG-4 ASP 640x480 30fps video, but MPEG-4 AVC can be a hard task even for the top Pentium IV. This processor may not cope with AVC HD (High Definition)! Such high requirements of MPEG-4 AVC make it difficult to design stand-alone players, although they are already appearing in the market.
