There are two ways cameras shoot slow motion: (1) Sensor and encoding frame rates are increased, with intention of retiming in the NLE, and (2) Sensor scan rate is increased but material is encoded at a lower frame rate and bit rate. IOW the slow motion is “baked in”. That is how the FX6 handles 120 fps material.
The FX6 can only do that frame rate in S+Q mode. I believe the reason for that restriction is the XAVC-I codec and MXF container format do not support the required encoding bit rate to shoot and record true 120 fps. In return the MXF container has much richer metadata than the MP4 container and better supports timecode.
The metadata which indicates the FX6 sensor frame rate is unfortunately esoteric, but it can be seen using Sony Catalyst Browse or the 3rd-party tools MediaInfo or Invisor. In Catalyst Browse, the metadata field is denoted “Capture frame rate”, as opposed to regular “frame rate”. In the other tools the metadata field is called “CaptureFrameRate_FirstFrame”.
I tried using the command-line utilities ExifTool, ffmpeg and ffprobe but they do not reveal that metadata. If they did you could batch process a bunch of camera clips and rename them to indicate the 120 fps stuff. Then you could use Finder tags or an FCP filter to keyword those.
I also investigated what video metadata is indexed by MacOS Spotlight search and what metadata fields Finder can search. Unfortunately they don’t handle sensor scan rate in XAVC-I/MXF.
However Invisor can display metadata from about 10 clips at the same time in a spreadsheet-like grid, so you can find them like that.
MediaInfo is a GUI tool but has an available command-line interface, but it’s limited and I don’t think it handles sensor scan rate.
FX6 in S+Q mode at 120 fps does not record audio, so maybe you could find them like that (maybe even in FCP). In hindsight that might be the simplest method but I didn’t think about it until just now.
Of course that doesn’t consider all the camera operators who shoot normal frame rate and forget to turn on their camera mics 🙂