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• With ffmpeg print onto clipped video hh:mm:ss time *from original* and hh:mm:ss total duration from original

  25 mai 2023, par Kes

  I am using arch linux and bash and ffmpeg, all are up to date and the latest versions.

  


  I am clipping a video that is 30 seconds long and wish to clip from 5 secs to 10 seconds to a new file, from the original.

  


  In the bottom right hand corner of the clip I wish to show timestamps from the original video as follows

  


  

  • in the 5th second "00:00:05/ 00:00:30"

  


  • in the 6th second "00:00:06/ 00:00:30"
    
etc

  


  • in the 10th second "00:00:10/ 00:00:30"

  


  


  This is an apparentley simple question(?) but the syntax of the command is not at all obvious and I am hoping an expert may shed some light on this.

  


  All I have so far for the drawtext part, which does not do what I want as it only counts the elapsed time from t=0 of the new clip, whereas I want it to show the timestamp and total duration of the original clip

  


  drawtext I started with

  


  "drawtext=text='%{pts\:gmtime\:0\:%M\\\\\:%S}':fontsize=24:fontcolor=black:x=(w-text_w-10):y=(h-text_h-10)"


  


  ffmpeg line with drawtext I have started with

  


  ffmpeg -ss 00:00:05 -i  "$in_file" -filter_complex "drawtext=fontfile=font.ttf:text='sample text':x=10:y=10:fontsize=12:fontcolor=white:box=1:boxcolor=black@0.5:boxborderw=5,drawtext=text='%{duration\:hms}':fontsize=12:fontcolor=black:x=(w-text_w-10):y=(h-text_h-10)" -t 5 -c:a copy -c:v libx264 out_file.mp4


  


• mp4 video written with ffmpeg has different first frame based on total number of frames

  26 janvier 2023, par Nitzan Weissman

  I'm trying to read and write videos using ffmpeg, and I got an interesting phenomenon where the first frame is not the same in videos I create that are made from the same frames, only with different lengths.

  


  The commands I'm running to reproduce the problem :

  


  ffmpeg -i .mp4 -frames:v 20 -q:v 3 resource_images/00%04d.png

ffmpeg -hide_banner -loglevel error -framerate 30 -y -i resource_images/00%04d.png  -c:v libx264 -pix_fmt yuv420p -frames:v 20 long_video.mp4 -y

ffmpeg -hide_banner -loglevel error -framerate 30 -y -i resource_images/00%04d.png  -c:v libx264 -pix_fmt yuv420p -frames:v 10 short_video.mp4 -y

ffmpeg -i long_video.mp4 -vf "select=eq(n,0)" -q:v 3 long_frame0.png -y

ffmpeg -i short_video.mp4 -vf "select=eq(n,0)" -q:v 3 short_frame0.png -y


  


  The images long_frame0.png and short_frame0.png are different (I loaded them using Python and compared them, there are many differences).

  


  I find it very peculiar, since I create very short videos, it's those videos first frames, and they are keyframes of those videos (I checked it using ffprobe)

  


  What is the cause of this issue and how do I overcome it to create a consistent first frame for a video, regardless of the video length ?

  


• mp4 video written with ffmpeg has different first frame based on total number of frames

  25 janvier 2023, par Nitzan Weissman

  I have a code that writes and reads videos in Python, I'm doing the writing using ffmpeg. I noticed a weird phenomenon, where the first frame changes based on the total number of frames in the video. I find it weird because the first frame is a key frame (I checked it using ffprobe)

  


  The code I'm using :

  


  The writing function

  


  import shutil
import subprocess
def write_h264_video(video_path: str, images: np.ndarray, fps: float):
    image_name_template = '00%04d.png'
    tmp_image_dir = (Path(video_path).parent / 'tmp_imgs')
    tmp_image_dir.mkdir()

    for ii, image in enumerate(images):
        cv2.imwrite(f'{str(tmp_image_dir / str(ii).zfill(6))}.png', image[..., ::-1])    
    command = f'ffmpeg -hide_banner -loglevel error -framerate {fps} -y -i {tmp_image_dir}/{image_name_template} ' \
            f' -c:v libx264 -pix_fmt yuv420p {video_path} -y'
    subprocess.call(command, shell=True)
    shutil.rmtree(tmp_image_dir)


  


  The main code

  


  import numpy as np
from pathlib import Path
import decord
decord.bridge.set_bridge('torch')

input_video_path = Path('')
tmp_path = Path('')
input_video = decord.VideoReader(str(input_video_path))

frames = np.zeros((20, 512, 512, 3), dtype = np.uint8)
for i in range(20):
    frames[i] = input_video[i].detach().cpu().numpy()
    
long_video_path = tmp_path / 'long_video.mp4'
short_video_path = tmp_path / 'short_video.mp4'

fps = 30
write_h264_video(str(long_video_path), frames, fps=fps)
write_h264_video(str(short_video_path), frames[:10], fps=fps)


long_video = decord.VideoReader(str(long_video_path))
short_video = decord.VideoReader(str(short_video_path))

long_frame_0 = long_video[0]
short_frame_0 = short_video[0]
(long_frame_0 == short_frame_0).all()


  


  I am supposed to get True, but I'm getting False.
I tried reading using other methods, using opencv for example, and the issue persists.
There are other ways to write videos of course, but I'm interested in ffmpeg-based ways.

  


  Thanks !