Is this video 50p or 25p? I have some footage shot with a Lumix DMC-FZ38 with the video format set to AVCHD and the SH (super high?) quality setting.

The manual says:


  [AVCHD Lite] (With audio)
  
  When set to [SH]: 1280x720 pixels
  
  (50p recording * /17 Mbps, only when card is used) /
  
  When set to [H]: 1280x720 pixels
  
  (50p recording * /13 Mbps, only when card is used) /
  
  When set to [L]: 1280x720 pixels
  
  (50p recording * /9 Mbps, only when card is used)
  
  *CCD output is at 25 fps


I think 50p means 50 progressive frames per second. According to advice given in the comments, CCD means "Charge Coupled Device", which is the type of sensor my camera uses. That would seem to indicate that the sensor outputs 25 frames per second.

When I import a video from the camera (00000.MTS) into Blender's Video Sequence Editor and tell it to use the frame rate from the video, it sets the project frame rate to 50fps. However, when I render it, the video plays at double speed, which seems to indicate that it was 25fps after all.

If I extract PNGs from the first second of the video using ffmpeg -i 00000.MTS -to 1 tmp%d.png, it gives me 25 png files, indicating 25fps.

ffprobe 00000.MTS reports:

Input #0, mpegts, from '01.MTS':
  Duration: 00:29:58.18, start: 0.366667, bitrate: 14025 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(tv, progressive), 1280x720 [SAR 1:1 DAR 16:9], 50 fps, 25 tbr, 90k tbn, 100 tbc
    Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 192 kb/s


According to this mailing list,


  tbr is guessed from the video stream and is the value users want to
  see when they look for the video frame rate, except sometimes it is
  twice what one would expect because of field rate versus frame rate.


So ffprobe reports both 50 fps and 25 tbr. Here tbr is half of fps, not double. What's the distinction here?

SMPlayer and VLC both report 50 frames per second.

What is the actual frame rate of my footage?
AVCHD Lite uses 25p/30p shooting rate and records it to 50p/60p container using frame doubling. Panasonic did that because, I presume, they were unable to shoot true 50p/60p at that time, on the other hand AVCHD and Blu-Ray specifications do not support 720p25 and 720p30 videos. Panasonic did this to stay compatible with the AVCHD format.

I guess the reason was that this way you can author the original clips as-is onto AVCHD Disc or Blu-Ray Disc, and they will be fully compliant and playable by standard Blu-Ray Player.

Nowadays a camera simply stores whatever it records in one of the standard containers like MP4, then you edit/author in whatever format you prefer. But ten years ago the compatibility between AVCHD and Blu-Ray was a selling point for both formats.