text: In the last year, videos of incidents between white police officers and minorities have prompted changes in procedures. Here is a look at those videos, which include graphic scenes of violence.
  
  They began as workaday interactions between the police and the public, often involving minor traffic stops in places like Cincinnati; North Charleston, S.C.; and Waller County, Tex. But they swiftly escalated into violent encounters. And all were captured on video.
  
  Those videos, all involving white officers and black civilians, have become ingrained in the nation’s consciousness — to many people, as evidence of bad police conduct. And while they represent just a tiny fraction of police behavior — those that show respectful, peaceful interactions do not make the 24-hour cable news — they have begun to alter public views of police use of force and race relations, experts and police officials say.
  
  Videos have provided “corroboration of what African-Americans have been saying for years,” said Paul Butler, a professor at Georgetown University Law School and a former prosecutor, who called them “the C-Span of the streets.” On Thursday, the family of Samuel DuBose, an unarmed black man who was shot to death by a University of Cincinnati police officer on July 19, said the officer would never have been prosecuted if his actions had not been captured by the body camera the officer was wearing.
  
  To the police, that poses a new challenge in trying to regain public confidence. “Every time I think maybe we’re past this and we can start rebuilding, it seems another incident occurs that inflames public outrage,” said James Pasco, the executive director of the Fraternal Order of Police. “Police officers literally have millions of contacts with citizens every day, and in the vast majority of those interactions, there is no claim of wrongdoing, but that’s not news.”
  
  Some polling bolsters such concerns. In a Gallup national survey conducted in June, 52 percent of people said they had “a great deal” or “quite a lot” of confidence in the police, down from 57 percent two years earlier, and 64 percent in 2004. In 2007, 37 percent of Americans had high confidence that their local police would treat blacks and whites equally, the Pew Research Center found, but last year that was down to 30 percent.
  
  At the same time, video may be changing the way prosecutors handle cases in which the police are accused of misconduct. Not only can video contradict an officer’s account of what happened, it can also create immense public pressure for action against officers.
  
  Such was the case with fatal police shootings in North Charleston and Cincinnati, and with the arrest in Baltimore of Freddie Gray, who died of injuries he sustained while in police custody. In all three cases, prosecutors brought rare murder charges against officers within days — remarkable speed for a process that in the past could take weeks or months. Those swift actions have been applauded by many African-Americans.
  
  But some prosecutors have raised concerns that the public outcry generated by video can also put pressure on prosecutors to file charges. “We don’t want to rush to judgment simply because of what the video shows,” said Peter Weir, the district attorney for Jefferson and Gilpin counties in Colorado, who says he believes police body cameras enhance public trust in the system.
  
  In the Cincinnati case, video from a camera worn by a University of Cincinnati police officer, Ray Tensing, provided crucial evidence, and contradicted the officer’s official account, in the July 19 shooting death of Mr. DuBose. A grand jury indicted Mr. Tensing, who was fired by the university police department on Wednesday, on charges of murder and manslaughter. He pleaded not guilty on Thursday in Hamilton County Municipal Court, and Judge Megan E. Shanahan set his bail at $1 million.
  
  Mr. Tensing later made bail and was released.
  
  There are no definitive figures, but officials say that most police forces do not use body cameras, or use them on a very limited basis. But according to a 2013 survey by the Police Executive Research Forum, a research group, about one in four of its member forces regularly used body cameras. And the number is rising quickly as the federal government provides grants for cameras, said Lindsay Miller, a senior research associate at the group.
  
  San Diego has equipped hundreds of its police officers with cameras and is expanding that program, and Los Angeles recently decided to put cameras on all of its patrol officers but has not yet done so. New York, Chicago, Houston, Philadelphia and other cities have trial programs.
  
  Dashboard cameras are far more prevalent — more so among state police and highway patrol forces than among local police forces — but experts say they know of no national tally of those, either.
  
  Yet despite the growing use of police video cameras, evidence is mixed about what effect they are having on police behavior. Experts say that cameras probably change for the better how the police and the public treat each other, but they do not know how much. And the fact that one viral video after another surfaces, showing officers treating civilians harshly, demonstrates the limits of that change.
  
  Recent studies showed that when officers in Rialto, Calif., and in Mesa, Ariz., wore body cameras, complaints against the police fell sharply. But body camera advocates and skeptics alike say they do not know how much that reflects a real decline in police misconduct, and how much was a drop in spurious civilian complaints; it may be that both groups behave better when they are on camera.
  
  “Over all, body cameras and dashboard cams deter police misconduct, but at this point, it’s hard to know how much, and there are officers whose behavior is not going to be changed,” Professor Butler said.
  
  The proliferation of video has coincided with a paradox: Public views of the police have grown worse, yet experts say police use of force has probably been lower in the last few years than in generations. (There is, however, no precise accounting of the number of people killed by police officers each year.)
  
  Polls show overwhelming public support for police body cameras — 92 percent in a New York Times/CBS News poll conducted April 30 to May 3. But law enforcement officials warn against unrealistic expectations of a simple transition that will provide a kind of impartial witness to every interaction.
  
  Routine use of cameras raises multiple questions for police departments: how to pay for them, how much discretion to give officers in turning cameras on and off, how long to store recordings, when to make them public, and how to safeguard the privacy of people, like crime victims, who might turn up on video.
  
  A collection of videos that have led to nationwide protests, federal investigations and changes in policy and attitudes on race.
  
  “The benefit of being able to hold police accountable in many situations where they are now largely immune is probably worth the cost alone,” said Jonathan Simon, the director of the Center for the Study of Law and Society at the University of California, Berkeley. “But even more so when you consider how often the same cameras will provide damning evidence against criminal suspects as well.”
  
  Police commanders and prosecutors generally support camera use, arguing that they provide useful evidence, and will usually show the officers conducting themselves professionally. Views among officers and the unions representing them are more mixed, varying from place to place.
  
  “A negative is that police might say, ‘We just won’t put ourselves in bad situations,’ that they say, ‘We are not going to jeopardize our lives because if we make a good-faith mistake, it is going to look like a crime, and we’re going to get prosecuted for murder,’ ” said Francis T. Cullen, a professor in the School of Criminal Justice at the University of Cincinnati.
  
  Another drawback, experts say, is that the public may have too much faith in video. It can give an incomplete, even misleading, picture, they say, and it cannot really put the viewer in the shoes of an officer having to make split-second decisions under pressure.
  
  “Body cameras are helpful, but they are not the magic elixir,” said Sim Gill, the district attorney of Salt Lake County, Utah. “What a camera sees is not necessarily what the officer sees. It’s not always going to be conclusive.”
  
  A version of this article appears in print on July 31, 2015, on page A1 of the New York edition with the headline: Glare of Video Is Shifting Public’s View of Police . Order Reprints| Today's Paper|Subscribe
summary: The recording of encounters between the police and the public has begun to alter public views of the use of force and race relations, experts and police officials say.