If you’re like me, you might have wondered what the difference is between MPEG-2, MPEG-4, H.264, AVCHD and H.265, and how they are related.
This article explains exactly this, without going into technicalities. By the end, you will have a clear idea of which is which, and which ones you should remember. If you’re totally new to all this, start by reading What is Video Compression?
We’ll use the following table as reference. Don’t read it just yet, but keep coming back to it as the article progresses, and everything will be clear. Click on the image to enlarge.
MPEG and ITU-T VCEG
In the beginning there was COST 211 (don’t worry, they don’t exist anymore). They created the H.120 standard, which basically flopped. But it paved the way for what we have today.
The ITU-T VCEG (Video Coding Expert Group) formed to improve upon H.120, and that’s all we have to know about that.
MPEG (Moving Pictures Experts Group) formed to find a way to incorporate codecs for broadcast work. To this day, the two committees – MPEG and VCEG, work side-by-side. MPEG specializes in broadcast (television), while the ITU (International Telecommunications Union) focuses on telecommunications (phone, internet).
In today’s world, their goals mostly overlap (because everything is going the way of the Internet), and this association is likely to continue.
This started it all, but didn’t do well. It had two versions, one for PAL and the other for NTSC.
H.261 and JPEG
JPEG (Joint Photographic Experts Group) became a popular codec of choice for images right about that time, and in the same ‘vein’, MPEG was formed to take care of the broadcast industry’s needs.
MPEG adopted H.261 and JPEG together to form what is called a ‘Suite’. The specific name for the first suite is MPEG-1.
It was limited to 1.5 Mbps, 4:2:0 and stereo audio only. At the time, there was PAL, NTSC and VHS, and that’s all it had to cater to.
Parts and Layers
MPEG suites have sub-divisions, called Parts. Traditionally, Part 1 is always for the ‘System’ (file format). Part 2 is for video, and Part 3 is for audio. Look at the image and you’ll see this clearly.
MPEG-1 Part 2 is also H.261, for our purposes.
Parts are further sub-divided into Layers. Audio has three or more layers, called Layer I, Layer II and Layer III and so on.
It just so happens that MPEG-1 Part 3 Layer III is called MP3. It does NOT stand for MPEG-3, but the third layer of the third part of the MPEG suite. This version of MP3 was also limited to stereo (two channels only).
In 1999, technology had advanced enough to warrant an upgrade of the suite.
Part 1 of the MPEG-2 suite had two major classifications: Program Stream and Transport Stream.
Part 2, video is also called H.262. It had additional support for interlacing and 4:2:2. The big change for audio was the addition of 5.1 channels, and MP3 was revised to incorporate this specification.
Most of broadcast television adopted MPEG-2, and it is still the most widely used codec today for broadcast. Additionally, DVD incorporated this technology, and was able to include surround sound as a result.
MPEG-2 also had more than three parts. The most important of these (not shown in the image) is Part 7, called the Advanced Audio Coding (AAC) audio format.
Professional camera codecs that use MPEG-2 include HDV and XDCAM.
By 2004 the world had suddenly discovered the Internet. MPEG was ready with the third suite, MPEG-4 (MPEG-3 was not used). This suite incorporates a whole lot of technology from the beginning of this century till 2012 or so.
Part 2, or technically MPEG-4 Part 2, is also called H.263. It included a new concept called ‘Profiles’ which we’ll look at last. HDCAM SR uses this specific Part.
Part 3 is still audio. AAC has been incorporated into Part 3.
MPEG-4 has about 30 parts, one for each technology. The two parts we are most concerned with are Parts 10 and 14.
H.264 or MPEG-4 Part 10/AVC
Part 10, or technically MPEG-4 Part 10, describes the AVC (Advanced Video Coding) format. This is H.264. Rather than start a new suite, they decided to add this as a Part.
H.264 is the most widely used codec on earth, even surpassing broadcast MPEG-2, simply due to the power of the internet. It is used by Youtube, and every other video provider of note.
It is also the codec that drives Blu-ray. Many broadcast pipelines and distribution channels have adopted H.264 (and MPEG-4 Part 2) as well.
Sony has added the XAVC codec (see the ‘AVC’ in the name?) to its line-up because XDCAM couldn’t deal with 4K and above.
Part 14 describes a container format for MPEG-4 codecs, as in *.mp4. That’s all this is.
Sony and Panasonic took the parts they liked about H.264 and called it AVCHD (MPEG-4 Part 10 AVC+HD). The key differences between AVCHD and H.264 is the former supports Dolby AC-3 encoding in addition to LPCM, and is limited by a total bit rate of 24 Mbps.
Whereas H.264 is designed as a distribution format (all MPEG suites are distribution formats, for the end user), AVCHD is designed for cameras as an acquisition format as well.
Quality-wise, there’s no difference.
AVCHD 2.0 keeps up with a newer version of H.264 with better compression and sampling. But it’s still 4:2:0 and is limited to 28 Mbps. Make no mistake, AVCHD is a consumer codec.
HEVC or H.265
As of 2013, the new kid on the block is MPEG-H. Part 2 (video, of course) is also called H.265 or HEVC (High Efficiency Video Coding). There are many vendors already claiming compatibility with this new format. Here are its key benefits:
- Up to 8K UHDTV (8192×4320 maximum)
- 12-bit color bit depth
- 4:4:4 and 4:2:2 chroma sub-sampling
- Supports up to 300 fps (earlier versions only supported up to 59.94 fps)
- Data rates of several GB/s
- File size ‘subjectively’ half the size of H.264 with better quality!
This is clearly the future. However, don’t bet on H.264 going away anytime soon. Who’s going to transcode the billions of H.264 videos already online?
The new reality of the MPEG suite, beginning with MPEG-4, is the concept of Profiles and Levels – in addition to Parts and Layers. Profiles are like presets, specific variants of the specification to be used for specific applications.
After all, the MPEG-4 specification with its thirty parts is quite large. Why would an encoder or software need to comply with all of it, if its chosen function is only for a specific need?
Profiles are unfortunately a necessary evil. Technology is moving too fast for committees to keep up, and many vendors don’t have to comply to the broadcast model anymore. Internet means freedom, and anyone can create a new variant of a codec (after paying the right licenses) and stream his or her videos in that proprietary format. Hell, you could even invent a completely new format, or encode your videos in H.120 if you like!