使用FFmpeg剪辑视频时遇-to值小于-ss错误的解决求助

Let's break down why you're hitting this error and fix it step by step:

The Root Cause #

FFmpeg's time format hh:mm:ss.xxx doesn't treat the decimal part as a frame number—it's a fraction of a second. When you pass 0:0:47.21, FFmpeg reads that as 47.21 seconds, not 47 seconds and 21 frames. Since your start time is 0:0:47.4 (47.4 seconds), 47.21 is indeed earlier than 47.4, hence the "value smaller than -ss" error.

For a 25fps video, each frame is 1/25 = 0.04 seconds. So 47 seconds and 21 frames translates to 47 + 21/25 = 47.84 seconds—not 47.21. That's the key mistake here.

Solution 1: Convert Frames to Proper Time Values #

First, calculate the actual time in seconds for your start/end points, then format it correctly for FFmpeg:

• Total seconds = (hours * 3600) + (minutes * 60) + seconds + (frames / fps)
• For your example:
  • Start: 0h0m47s4f → 47 + 4/25 = 47.16 seconds → format as 00:00:47.16
  • End: 0h0m47s21f → 47 + 21/25 = 47.84 seconds → format as 00:00:47.84

Solution 2: Update Your Python Code to Automate the Conversion #

Replace your manual string concatenation with code that calculates the correct time values. Here's the revised version:

import os

fps = 25  # Match your video's frame rate
inputvideo = "your_input_file"
outputvideo = "your_output_file"

# Example values: fhours=0, fminutes=0, fseconds=47, fframes=4
#                lhours=0, lminutes=0, lseconds=47, lframes=21

# Calculate total seconds for start and end times
start_total = fhours * 3600 + fminutes * 60 + fseconds + fframes / fps
end_total = lhours * 3600 + lminutes * 60 + lseconds + lframes / fps

# Format into FFmpeg-compatible time string (hh:mm:ss.xx)
def format_time(total_seconds):
    hours = int(total_seconds // 3600)
    minutes = int((total_seconds % 3600) // 60)
    seconds = total_seconds % 60
    return f"{hours:02d}:{minutes:02d}:{seconds:.2f}"

start_time = format_time(start_total)
end_time = format_time(end_total)

# Build and run the command
command = f'ffmpeg -i {inputvideo}.mp4 -qscale:v 2 -vf scale=427:240 -ss "{start_time}" -to "{end_time}" {outputvideo}.avi'
os.system(command)

Bonus: Frame-Exact Trimming with Filters #

If you want to avoid time conversion entirely and work directly with frame numbers, use FFmpeg's select and setpts filters. This is more reliable for frame-precise cuts:

ffmpeg -i input.mp4 -qscale:v 2 -vf "scale=427:240,select='between(n,START_FRAME,END_FRAME)',setpts=N/FRAME_RATE/TB" output.avi

• Replace START_FRAME and END_FRAME with the actual frame numbers (counting starts at 0). For your example:
  • Start frame: 0*3600*25 + 0*60*25 + 47*25 +4 = 1179
  • End frame: 0*3600*25 +0*60*25 +47*25 +21=1196

You can also integrate this into your Python code by calculating the frame numbers directly instead of time values.

内容的提问来源于stack exchange，提问作者dusa