Digital Video updated 030109 and an update on
Audio 030205
The purpose of this page is mainly for my own understanding. The structure is
preliminary and will change.
The picture is rather complicated. Lots of development going, lots of opinions
and lots of very good pages. So the update of this page rest for a while. I am
in no hurry.
DV and Interlace
35 mm movies are usually scanned at 4096 horizontal pixels (called "4K") at 24
frames/sec.
A TV picture is built up by lines in two scans. Each scan
is called a field. Two fields is a frame.In the
first pass line 1,3,5,7 etc and in the other line 2,4,6,8 etc are scanned. This
is called interlacing. PAL's resolution is 625 horizontal lines, but only 576 of
these are used for the picture. PAL's vertical frequency is 50 Hz producing 25
frames/sec. The TV picture quality is usually measured in how many lines you can
se. On a good TV you can see up to 400 lines. VHS is up to 250 lines. A DVD up
to 540 lines but the TV set don't handle it.
With full PAL resolution 768*576 (= 442 368 pixels), a framerate of 25 frames/s
and 24 bits to record uncompressed RGB (8 bits each för red, green and blue) we
end up with 265 421 000 bits = 33 177 000 bytes / 1024 = 32 400 KB / 1024 = 31,
6 MB. 31,6 MB/sec takes a lot of room on a harddisk. We have to compress.
The technique of converting movies 24 frames/s to the TV's 25 frames is called
Telecine. I will not go in to that except for the practical considerations. What
are they?
Then we also have progressive images. That is a frame that is not interlaced.
Video Compression (codec's)
Codec's are identified by a
FOURCC (Four Character Code). See
www.fourcc.org is a means to identify a video data stream format. This is NOT
file extensions or Internet Media (MIME) types.
Resolution for the PAL system:
MPEG: variety of frame-sizes, frame-rates, and
data-rates. MPEG stores only certain complete frames (keyframes) and the
difference between the frames. It is more to this. Will maybe came later.
MPEG-2: DVD at least 768*576 pixels. (DVD Quality)
MPEG-2 on CD: SVCD (Super VCD) at least 480*576 pixels. (S-VHS Quality). max
2600 kbps VBR.
MPEG-1: VCD (video CD) at least 352*288 pixels. CBR. (nearly VHS Quality)
DV: Fixed rate of 3.5 MB/sec. DV (and M-JPEG) stores each frame as a
complete image. DV is stored in avi-files of type 1 or type 2. Type 1 stores
video and audio in one data stream. Type 2 separates video and audio in two data streams.
M-JPEG: For Hi8 and SVHS quality, 3 MB/sec or more.
For VHS 1 MB/sec. A good format for editing.
MPEG-4: This is NOT straightforward! There are many "versions"
Robert Batchelder, Gartner
Analyst:
"There's no question that MPEG-4 is going to succeed MPEG-2 as the
standard for streaming digital video."
MPEG-4 is an ISO standard but many
proprietary solutions exists. About
standardization, see MPEG-4 Industry Forum,
www.m4if.org, MPEG’s home page,
mpeg.telecomitalialab.com and
Internet Streaming Media Alliance,
www.isma.tv
One good article on MPEG-4,
www.benwaggoner.com/articles/DV0105Mpeg4v3f.3.pdf
MPEG4IP is the Open Source project. You can
download the MPEG4IP package to get practical experience.
Microsoft's version of MPEG-4 v1/2/3 and DivX are proprietary solutions that
offer similar performance, but MPEG-4 has the advantage of being an industry
standard.
Microsoft has now renamed its format to "Windows Media Format"
See
http://www.mediable.net/se/res/streaming/arkitektur_mwm.html about the
format not being a standard.
DivX is a hack that lets the MS MPEG-4 v3 codec be used inside an AVI
file. It's often linked with the DVD ripping subculture and often referred to as
MPEG-4, which it is not.
OpenDivX: The OpenDivX code is based on the MPEG-4 video standard.
Project Mayo owns the copyrights to the code.
Project Mayo is a company created by
the DivX project founders.
XviD is an ISO MPEG-4 compliant video codec. See also
www.doom9.org/index.html?/xvid.htm on how to do
H.264, also known as JVT/AVC, claims that it can deliver
DVD-quality broadcasts over the Internet using considerably less network
resources than rivals.
Recommendation H.264 of the United Nations' International Telecommunication
Union (ITU), won't be ready for public
consumption until March--three months behind schedule.
While the ITU refers to the codec as Recommendation H.264, ISO calls it
ISO/IEC 14496 10 Advanced Video Coding (AVC).
The latest audio portion of the standard, called AAC, is the equivalent of MP3.
The MPEG-4 organization will hold a final vote in March on whether to make
AACPlus part of the evolving audio standard.
Will the MPEG-4 standard be a standard? We will see. The content will drive.
..or the widespread popularity of media players from Microsoft and RealNetworks contribute
to the decision to choose these technologies.
A few MPEG-4 products
RealNetworks announced support for the MPEG-4 standard in its latest release.
EnvivioTV - has a MPEG-4 player for Windows Media Player, RealPlayer,
and QuickTime Player. EnvivioTV is available as a plug-in for Apple QuickTime v
4.1.2 or higher, the RealNetworks player v 7.0 or higher, and Windows Media
Player v 6.4 or higher.
www.mpegable.com has a ISO
MPEG-4 codec, player. plug-in, etc Read news article on
www.internetvideomag.com/news2002/07-12-02dicas-MPEG4.htm
www.sigmadesigns.com has a single-chip DVD decoder with MPEG-4, MP3 and WMA playback and a free
Software Encoder and Decoder for ISO MPEG-4 Video.
Audio
I skip au, aiff and several others.
What is the best audio codec with respect to quality? See test at http://www.telos-systems.com/techtalk/aacpaper_2/aacpaper_8.htm
WAVE
PCM format
The WAVE file format is a subset of Microsoft's RIFF specification. MS-Wave
format is the standard in the PC digital-audio world and uses uncompressed pulse
code modulation (PCM). Is used in the Audio CD.
MPEG-2 AAC
(Advanced Audio Coding) and BC (Backward Compatible)
MPEG-2 audio exists in two standards MPEG-2 BC (ISO/IEC 13818-3) and MPEG-2 AAC
(ISO/IEC 13818-7).
The official audio codec for MPEG-4 is also AAC.
MPEG-4 AAC is the official audio codec for MPEG-4 and is an enhancement
to MPEG-2 AAC. See http://www.vialicensing.com/products/mpeg4aac/standard.html
or http://www.eetimes.com/story/OEG20011218S0048
For free MPEG-2 and MPEG-4 AAC codecs see http://faac.sourceforge.net
MPEG4 CELP for coding speech at the lowest bit-rates
(e.g. < 14 kb/s).
AC-3 (Dolby Digital, 5.1 format)
AC-3 is a high-quality, low-complexity multichannel audio coder. See http://www.dolby.com/tech/ac-3mult.html
mp3
The Mp3 format (MPEG-1 layer 3) is well known, so I leave it with that.
MP3Pro
MP3Pro from Coding Technologies.
They have created MP3Pro which encodes wavefiles at 64 kbps with the same
quality as MP3 at 96-128 kbps. MP3Pro can be played in a mp3 player.
aacPlus(tm)
Coding Technologies have also
created aacPlus(tm) to provide excellent quality stereo audio programming at
48Kbps. aacPlus is the combination of MPEG AAC and Coding Technologies' SBR
(Spectral Band Replication) technology. SBR is a bandwidth extension technique,
which enables audio codecs to deliver the same quality at half the bit rate. An
interesting example of this is "Digital Radio
Mondiale"
Ogg Vorbis
The Ogg Vorbis format is an open-source
alternative to the MP3 format from the Xiph Foundation. Ogg Vorbis creators are hoping their
technology's size and quality puts it on par with software such as
MPEG-4 Ogg Vorbis is a
fully Open, non-proprietary, patent-and-royalty-free, general-purpose compressed
audio format,
www.xiph.org/ogg/vorbis/index.html
One opinion: "An Ogg file is10
times smaller then mp3 and the quality is much better....". True?
File formats
File formats are like the envelope around several audio, video and subtitle
streams. Maybe the most common format is AVI (Audio-Video Interleave). AVI
files are limited to 4
GB in FAT32 or to 2GB if OpenDML not is supported.
Other formats are ASF (Advanced Streaming
Format), MOV (Quicktime), RM (RealMedia), MP4 (MPEG-4 container), and MPEG (MPEG-1/2
container). One of the main problems of AVI is that you can't stream it over
internet connections.
That's why ASF was invented.
Some formats is only suitable for delivering (MPEG- 4, AMR, MPEG-1, MP3,
Real/WinMedia, etc) and some is also suitable for authoring (AAC, MPEG-2, MJPEG,
etc). ITU-T601 just for authoring.
There exist an open Audio/Video container format, MCF (Media Capsuline Format) as the
open source alternative
to existing containers. Se the MCF Specifications (in deep) at http://mcf.sourceforge.net/docbook/spec.html
Se also AVI, Ogg and MCF - A Comparison of different
Multimedia Container Formats.
MIME types
MIME (Multipurpose Internet Mail Extension) is a standard for describing
different types of information and allow file exchange. There need to be an
application associated with each file type in both Web browsers and Web servers
when streaming video/audio.
MIME Media Types : http://www.iana.org/assignments/media-types/
or http://www.ltsw.se/knbase/internet/mime.htp
MIME Type Settings for Windows Media Services: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/mime.asp
Streaming from a Web Server: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/webserver.asp
QuickTime Streaming: http://www.fastvirtual.com/support/multimedia/quicktime.html
Example of Supported MIME Types from an ISP: http://www.fastvirtual.com/support/multimedia/mime.html
A few links
It is unlikely that any video technology will be created any time soon that is
wholly 'free'
www.tele.ntnu.no/signal/courses/musibe/foiler/MPEG-4overview.pdf
http://www.vcdhelp.com/tools Lots of video tools!
dvd.box.sk mainly DivX SW
www.emedialive.com
news etc
www.streamingresources.com Streaming news, forums
Internet Video Magazine, www.internetvideomag.com
(old) Codec Comparisons:
www.extremetech.com/article2/0,3973,53956,00.asp
About
the
Sigma codec and Xvid
www.tradwell.com.tw/download/rmp4file.htm
See www.dvddemystified.com/dvdfaq.html
and a simpler lonestar.texas.net/~bdub/earl/dvd.htm