Not necessarily. It would seem almost common sense that the district attorney’s office would dismiss your case if your breath or blood was under the legal limit. However, I’ve seen prosecutor’s refuse to dismiss the case out right for a few reasons.
The first reason being that the prosecutor believes they can prove one of the other definitions of intoxication. (See definitions of legal intoxication here). The prosecutor in this case after watching your video and seeing the Standard Field Sobriety tests, thinks they can prove to a jury that you lost the normal use of your mental or physical faculties due to the introduction of alcohol or drugs.
The second reason your case might not be dismissed out right is because the prosecutor will argue that even though your BAC was under the legal limit when the officer took your breath/ blood sample, your BAC was higher at the time of driving. Just because you had alcohol earlier in time, it does not mean that your BAC was always higher earlier in time. It takes time (30 min up to 2 hours) for the body to absorb alcohol; your BAC will be rising during this phase. Then your body starts eliminating the alcohol, and your BAC will begin to decline.
If a prosecutor has certain information, they will try to do what is known as retrograde extrapolation. This is a calculation based on certain information that you gave the officer to calculate what your BAC was at the time you were driving.
Finally, some prosecutors will not dismiss your case outright when there is a combination of drugs and alcohol in your body. Even if you might be under the legal limit for alcohol, and only have prescriptions in your system, some prosecutors will try to argue that you were intoxicated because of the combination of the two substances.