Question: All references frames that are in free fall are what?
About the article "General relativity", section "Relativistic generalization".

Candidate passages:
A comparison can be made between Newtonian relativity and special relativity.
Some of the assumptions and properties of Newton's theory are: The existence of infinitely many inertial frames.
Each frame is of infinite size (covers the entire universe).
Any two frames are in relative uniform motion.
(The relativistic nature of mechanics derived above shows that the absolute space assumption is not necessary.)
The inertial frames move in "all" possible relative uniform motion.
There is a universal, or absolute, time.
Two inertial frames are related by a Galilean transformation.
In all inertial frames, Newton's laws, and gravity, hold.
In comparison, the corresponding statements from special relativity are as follows: Rather than allowing all relative uniform motion, the relative velocity between two inertial frames is bounded above by the speed of light.
Instead of universal time, each inertial frame has its own time.
The Galilean transformations are replaced by Lorentz transformations.
In all inertial frames, "all" laws of physics are the same.
Notice both theories assume the existence of inertial frames.
In practice, the size of the frames in which they remain valid differ greatly, depending on gravitational tidal forces.
In the appropriate context, a "local Newtonian inertial frame", where Newton's theory remains a good model, extends to, roughly, 107 light years.
In special relativity, one considers "Einstein's cabins", cabins that fall freely in a gravitational field.
According to Einstein's thought experiment, a man in such a cabin experiences (to a good approximation) no gravity and therefore the cabin is an approximate inertial frame.
However, one has to assume that the size of the cabin is sufficiently small so that the gravitational field is approximately parallel in its interior.
This can greatly reduce the sizes of such approximate frames, in comparison to Newtonian frames.
For example, an artificial satellite orbiting around earth can be viewed as a cabin.
However, reasonably sensitive instruments would detect "microgravity" in such a situation because the "lines of force" of the Earth's gravitational field converge.
In general, the convergence of gravitational fields in the universe dictates the scale at which one might consider such (local) inertial frames.
For example, a spaceship falling into a black hole or neutron star would (at a certain distance) be subjected to tidal forces so strong that it would be crushed.
In comparison, however, such forces might only be uncomfortable for the astronauts inside (compressing their joints, making it difficult to extend their limbs in any direction perpendicular to the gravity field of the star).
Reducing the scale further, the forces at that distance might have almost no effects at all on a mouse.
This illustrates the idea that all freely falling frames are locally inertial (acceleration and gravity-free) if the scale is chosen correctly. 
While Maxwell's equations are invariant under Lorentz transformations, the GEM equations were not.
The fact that ρg and "j"g do not form a four-vector (instead they are merely a part of the stress–energy tensor) is the basis of this problem.
Although GEM may hold approximately in two different reference frames connected by a Lorentz boost, there is no way to calculate the GEM variables of one such frame from the GEM variables of the other, unlike the situation with the variables of electromagnetism.
Indeed, their predictions (about what motion is free fall) will probably conflict with each other.
Note that the GEM equations are invariant under translations and spatial rotations, just not under boosts and more general curvilinear transformations.
Maxwell's equations can be formulated in a way that makes them invariant under all of these coordinate transformations. 
  I-frames are coded without reference to any frame except themselves.
May be generated by an encoder to create a random access point (to allow a decoder to start decoding properly from scratch at that picture location).
May also be generated when differentiating image details prohibit generation of effective P or B-frames.
Typically require more bits to encode than other frame types.
Intra coded frames/slices (I‑frames/slices or Key frames).
Often, I‑frames are used for random access and are used as references for the decoding of other pictures.
Intra refresh periods of a half-second are common on such applications as digital television broadcast and DVD storage.
Longer refresh periods may be used in some environments.
For example, in videoconferencing systems it is common to send I-frames very infrequently. 
As intriguing as geometric Newtonian gravity may be, its basis, classical mechanics, is merely a limiting case of (special) relativistic mechanics.
In the language of symmetry: where gravity can be neglected, physics is Lorentz invariant as in special relativity rather than Galilei invariant as in classical mechanics.
(The defining symmetry of special relativity is the Poincaré group which also includes translations and rotations.)
The differences between the two become significant when we are dealing with speeds approaching the speed of light, and with high-energy phenomena.
With Lorentz symmetry, additional structures come into play.
They are defined by the set of light cones (see the image on the left).
The light-cones define a causal structure: for each event A, there is a set of events that can, in principle, either influence or be influenced by A via signals or interactions that do not need to travel faster than light (such as event B in the image), and a set of events for which such an influence is impossible (such as event C in the image).
These sets are observer-independent.
In conjunction with the world-lines of freely falling particles, the light-cones can be used to reconstruct the space–time's semi-Riemannian metric, at least up to a positive scalar factor.
In mathematical terms, this defines a conformal structure.
Special relativity is defined in the absence of gravity, so for practical applications, it is a suitable model whenever gravity can be neglected.
Bringing gravity into play, and assuming the universality of free fall, an analogous reasoning as in the previous section applies: there are no global inertial frames.
Instead there are approximate inertial frames moving alongside freely falling particles.
Translated into the language of spacetime: the straight time-like lines that define a gravity-free inertial frame are deformed to lines that are curved relative to each other, suggesting that the inclusion of gravity necessitates a change in spacetime geometry.
A priori, it is not clear whether the new local frames in free fall coincide with the reference frames in which the laws of special relativity hold—that theory is based on the propagation of light, and thus on electromagnetism, which could have a different set of preferred frames.
But using different assumptions about the special-relativistic frames (such as their being earth-fixed, or in free fall), one can derive different predictions for the gravitational redshift, that is, the way in which the frequency of light shifts as the light propagates through a gravitational field (cf.
below).
The actual measurements show that free-falling frames are the ones in which light propagates as it does in special relativity.
The generalization of this statement, namely that the laws of special relativity hold to good approximation in freely falling (and non-rotating) reference frames, is known as the Einstein equivalence principle, a crucial guiding principle for generalizing special-relativistic physics to include gravity.
The same experimental data shows that time as measured by clocks in a gravitational field—proper time, to give the technical term—does not follow the rules of special relativity.
In the language of spacetime geometry, it is not measured by the Minkowski metric.
As in the Newtonian case, this is suggestive of a more general geometry.
At small scales, all reference frames that are in free fall are equivalent, and approximately Minkowskian.
Consequently, we are now dealing with a curved generalization of Minkowski space.
The metric tensor that defines the geometry—in particular, how lengths and angles are measured—is not the Minkowski metric of special relativity, it is a generalization known as a semi- or pseudo-Riemannian metric.
Furthermore, each Riemannian metric is naturally associated with one particular kind of connection, the Levi-Civita connection, and this is, in fact, the connection that satisfies the equivalence principle and makes space locally Minkowskian (that is, in suitable locally inertial coordinates, the metric is Minkowskian, and its first partial derivatives and the connection coefficients vanish).
These are stock cars custom built for racing, usually with welded tubular frames and custom built or purchased bodies.
The most popular type of dirt full bodied stock cars are late models.
They are categorized depending on what track and series that is running.
The racetrack dictates what type of late model is raced, but most fall in to one of these categories: