Regardless of the grounds you might have for an appeal, the appeals court must be convinced that the legal issue is such that it denied you the opportunity to receive a fair trial. If your ground for appeal is that the trial judge allowed a video tape into evidence that was taken of you entering a store where a crime occurred, an appellate court might agree with your attorney that the tape was illegally seized by police and should not have been allowed at trial. This does not, automatically, mean that your conviction will be overturned.
If prosecutors had five eyewitnesses putting you at the scene of the crime, the admissibility of the video might be a moot point. Even without the video, there was sufficient evidence to support the conclusion drawn by the jurors that you were at the scene of the crime. The mistake made by the judge was, therefore, harmless error that did not affect the outcome of the case.