When you're talking about video formats, you have to talk about two
things: the type of video encoding and the type of file that is
wrapped around the encoded video. Actually, you also have to worry
about how the audio is encoded, because for most video formats, there
are choices of audio coding and wrapping. In many cases, however,
there's a most common way of dealing with audio.
(just a little bit below, there's a ** after JPEG, because image
compression works the same way: technically, there's no such thing as
a "JPEG image file" because JPEG is a standard for image compression,
the files that we all name abc.jpg are actually JFIF's - JPEG File
Interchange Format - or EXIF's: Exchangeable Image file Format)
Starting with the DV tapes:
The format on DV tapes is called DV.
It compresses each frame individually using a compression algorithm
similar to JPEG** (DCT - discrete cosine transform - also used in
MPEG-4 Part 2 / DivX). Frame size is 720 pixels per line for both 4:3
and 16:9 frame aspect ratios, which means the pixels have to be
different sizes for fullscreen and widescreen video. The # of lines
per frame depends on whether it's 50 or 60 Hz, and I assume the
different frequencies come up because we have 60Hz AC in N.America vs.
50 in Europe. 60Hz system has 480 lines.
The avis I get when I transfer files from tape to computer are DV
video wrapped in an AVI container. There are two types of wrapping:
with Type 1 the multiplexed audio and video is saved into the video
section of a single AVI file, with Type 2 only video is saved in AVI
file, audio is saved in a separate file. Type 2 is rare, it's almost
always Type 1
The audio is two channels (stereo) of 16-bit resolution and 48 kHz
sampling rate (CDs are 44.1kHz) PCM (pulse-code modulation - same as
on CDs) sound.
http://en.wikipedia.org/wiki/DV
DVDs and MPEGs
There umpteen standards with MPEG in the name...
DVDs use MPEG-2 compression of their video. As with DV, it's
different for 50Hz, but in N.America DVDs frames are 720x480 pixels
and the frame rate is 23.976 frames/second (dunno why it doesn't come
out to exactly 24).
The container files are called MPEG-PS (Program Stream), so this is
why I get confused because the encoding and the wrapper file are both
just called "MPEG." It gets worse: The container files on a DVD have
a .VOB extension because they are a special type of MPEG-PS file with
extra information. MPEG files are typically .mpg or .mpeg
The audio data on a DVD movie can be PCM, DTS, MPEG-1 Audio Layer II
(MP2), or Dolby Digital (AC-3) format, this is one of the reasons for
the .vob file, a basic .mpg file can't contain DTS or AC3 audio data
(DTS and AC3 are competing formats for movie and home theatre sound).
http://en.wikipedia.org/wiki/DVD-Video
http://en.wikipedia.org/wiki/MPEG_program_stream
http://en.wikipedia.org/wiki/Dts_audio
I don't know and am not going to find out about the details of
converting the DV video to DVD. This link has some info, I wonder if
this is what Deo does:
http://www.transcoding.org/transcode?DVtoDVD
Digital Video Cameras
Just before our last trip to Disneyland, our Canon Camera died and we
bought a JVC Everio that records on a hard drive. (We didn't like the
way it worked, so we returned it later).
This stores mpeg video in an .MOD container file. .mod is another
special type of .mpg container file.
http://en.wikipedia.org/wiki/MOD_and_TOD_(video_format)
Digital cameras
Our Canon camera can take movies as well, but just mono sound. I
haven't found any details about how the video is encoded. The files
it stores on the memory card are .avis.
Ok, I looked into this a bit more just now and found that most digital
cameras store videos in Motion JPEG format:
http://en.wikipedia.org/wiki/Motion_JPEG
It's not very good quality and not great in terms of compression, it
gets used in digital cameras because it's easy to implement: the
camera already does JPEG compression of pictures, apparently it's easy
to implement M-JPEG for video.
While looking this up, I found some recommendations for a program
called GSpot which seems to have a comprehensive internal database of
codecs and gives a bunch of information on video files:
http://www.headbands.com/gspot/
Finally, on to the modern encodings
MPEG-4 Part 2 is the compression standard used by DivX and XVid codecs.
MPEG-4 Part 10 is also called H.264 or AVC. (Or sometimes a
combination like MPEG-4 Part 10 AVC). H.264 is used on Blue-Ray
disks.
http://en.wikipedia.org/wiki/MPEG-4_Part_2
http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC
As always, those are the compression standards, there are a few
different container files.
You can have divx video inside avi files, but that's what started my
several hours wasted on research: apparently that's not a great
option, and some software has already stopped supporting it. Yet
another standard MPEG-4 Part 14 defines a container file format which
usually gets the extension .MP4 But Apple started using .M4A at some
point, and apparently .M4V is also sometimes used. It's supposed to
be .mp4
http://en.wikipedia.org/wiki/Audio_Video_Interleave
http://en.wikipedia.org/wiki/MPEG-4_Part_14
Finally, there's an open-source standard that defines a file type .mkv
that's named after the Russian nesting dolls (matryoshka / Матрёшка).
http://en.wikipedia.org/wiki/Matroska
MPEG-4 has more options and possibilities for audio than MPEG-2, too
many for me to sort out. It looks like AAC is what's used on BluRay
DVDs.
So for my current use, I'm gonna transcode the avis from the videocam to divx, later I might do it again for H.264. I'll be using Handbrake for most of the transcoding, I'm not sure if it'll work on the motion Jpeg videos from the still camera.
