How to get duration of webm video file when duration is not explicitly defined

Question

I have a segment of a webm file with an incomplete header, I want to cut this segment down to 10 seconds by trimming x seconds off the front of the file, however I am unable to use the -sseof tag because the end of the file isn't defined. I have discovered that if I ask ffmpeg to pull out the audio or video from the file it responds with some data long the lines of size=212kB time=00:00:13.32 bitrate= 130.2kbits/s speed=1.79e+03x video:0kB audio:210kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.991311% Showing that there is 13.32 seconds of data in the file, however if I use ffprobe for the file length it replies with N/A. Is there a way to get that 13.32 value by itself without encoding the webm file?

Answer 1

You could use python and opencv to get the details of the video then pass them to:

import cv2
file = os.path.basename(filename)
video_file = filename
cap = cv2.VideoCapture(video_file)

# get video details
framespersecond= int(cap.get(cv2.CAP_PROP_FPS))
video_total_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
duration = video_total_frames/framespersecond
end_time = duration - 10

# Something like this to clip with ffmpeg.
ffmpeg_extract_subclip(file, start_time, end_time, targetname="test.mp4")

Answer 2

Try

ffprobe -hide_banner -loglevel quiet \
        -of default=nk=1:nw=1 -show_entries format=duration INPUT_FILE

This command just prints the total duration in seconds.

Answer 3

I was informed that:

ffprobe -v 0 -hide_banner -of compact=p=0:nk=1 -show_entries packet=pts_time -read_intervals 99999%+#1000 input.webm | tail -1

will return the timestamp of the last packet of data. This is what I was looking for.