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Preprocessing

All preprocessing is applied at load time by passing arguments to MgVideo. Steps execute in a fixed order: trim → skip → fix → rotate → contrast/brightness → crop → grayscale. This page is a task reference; the topic is taught in course form in chapter 3 of the wiki.

Trim, skip, rotate, adjust

import musicalgestures as mg

mv = mg.MgVideo('/path/to/video.avi', starttime=5, endtime=15, skip=3,
                rotate=90, contrast=100, brightness=20)

starttime and endtime are in seconds; skip=n keeps every (n+1)th frame; rotate accepts any angle in degrees (including fractional values such as 5.31); contrast and brightness are percentages in the range −100 to 100, where 0 leaves the video unchanged.

Crop and grayscale

mv = mg.MgVideo('/path/to/video.avi', crop='auto')      # crop to the region of motion
mv = mg.MgVideo('/path/to/video.avi', crop='manual')    # draw the rectangle yourself
mv = mg.MgVideo('/path/to/video.avi', color=False)      # grayscale mode

crop='manual' opens a window where you draw the crop rectangle, then press c to confirm or r to reset. color=False keeps all subsequent processes in grayscale mode, which can reduce processing time.

Fix a frame count

mv = mg.MgVideo('/path/to/video.avi', frames=1000)
mv = mg.MgVideo('/path/to/video.avi', frames=-1)    # keyframes only

Extracts a fixed number of frames, useful for batch processing files of different lengths.

Resample (frame rate, speed, frame decimation)

mv25 = mv.resample(fps=25)         # retime to 25 fps (duration-preserving)
fast = mv.resample(speed=2.0)      # play 2× faster (video + audio retimed in sync)
dec  = mv.resample(skip=2)         # discard 2 frames for every one kept

resample() returns a new MgVideo and leaves the original untouched. When operations are combined they apply in order skip → speed/fps; the output name defaults to the input name with a _resampled suffix, and target_name and overwrite work as for the other methods.

Keep intermediate files

mv = mg.MgVideo('/path/to/video.avi', starttime=5, endtime=15, skip=3,
                rotate=90, crop='auto', keep_all=True)

By default only the final preprocessed video is kept; keep_all=True retains each step's result as files like video_trim.avi, video_trim_skip.avi, video_trim_skip_rot.avi, and so on.

Output file names and overwriting

mv = mg.MgVideo('/path/to/video.avi')
mv.history(target_name='/output/my_history.avi', overwrite=False)   # keep every run

Every analysis method accepts these two parameters. target_name sets the output path; if None (default), a suffix is appended to the source name, so history on dance.avi produces dance_history.avi. overwrite=True (default) replaces the existing file in place; overwrite=False silently increments the name (dance_history_0.avi, dance_history_1.avi, …), keeping every run.

Further