Update main.rs

Author: t-nil

av1an/src/main.rs

@@ -510,8 +510,12 @@ pub struct CliOpts {
   #[clap(long, default_value_t = 4, help_heading = "Target Quality")]
   pub probes: u32,
 
-  /// Framerate for probes, 1 - original
-  #[clap(long, default_value_t = 1, help_heading = "Target Quality")]
+  /// Only use every nth frame for VMAF calculation, while probing.
+  ///
+  /// WARNING: The resulting VMAF score might differ from if all the frames were used; usually it should be lower,
+  /// which means to get the same quality you must also usually lower the --target-quality. Going higher than
+  /// n=4 usually results in unusable scores, so this is disabled.
+  #[clap(long, default_value_t = 1, value_parser = clap::value_parser!(u16).range(1..=4), help_heading = "Target Quality")]
   pub probing_rate: u32,
 
   /// Use encoding settings for probes specified by --video-params rather than faster, less accurate settings