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joplin notion extension/Web Development/Extras/ffmpeg.md
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joplin notion extension/Web Development/Extras/ffmpeg.md
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ffmpeg
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- For recording a particular section of video
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https://superuser.com/questions/639402/convert-specific-video-and-audio-track-only-with-ffmpeg
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`ffmpeg -i input.video -ss hh:mm:ss.ms -t ss output.video`
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Eg :
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`ffmpeg -i inputVideo.mkv -ss 00:34:12.00 -t 20 outputVideo.mkv`
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This will start recording from 34th min 12th sec to 34th min 32sec as 20 after -t is 20s
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- Choosing codecs, audio tracks
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`ffmpeg -i Mr.Robot.S01E03.720p.Hindi.English.moviesFlixPro.in.mkv -ss 00:35:18.00 -t 50 -c:v libx264 -c:a ac3 -crf 20 -map 0:0 -map 0:1 recorded1.mp4`
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-c:v : video codec libx264 means popular H.264
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-c:a audio codec ac3 is audio codec
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-crf : constant rate factor
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map is for stream id so 0 represents 1st, 1 represents 2nd and so on. but this can be overwelming and confusing t know which one is audio stream or video stream or subtitles or something else
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`ffmpeg -i inputVideo.mkv -ss 00:35:18.00 -t 50 -c:v libx264 -c:a ac3 -crf 20 -map 0:v:0 -map 0:a:1 recorded1.mp4
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`
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`-map 0:v:0` means 1st video track
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`-map 0:a:1` means 2nd audio track so if there r 2 audio track 2nd audio track will be encoded
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ac3 audio track may not work in browser so choose `aac` as audio track
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or
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`ffmpeg -i "Texas Police Chief arrests woman over facebook post warning neighbors about dirty tap water.mp4" -ss 00:07:00.00 -t 20 -c:v libx264 -crf 20 -map 0:v:0 -map 0:a:0 life_is_political.mp4`
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- extracting video including subtitle
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- first extract subtitle file
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`ffmpeg -i input.mkv -map 0:s:0 -c:s srt subtitles.srt`
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or
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`ffmpeg -i input.mkv subtitles.srt`
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- then use some script or use online tool like https://subshifter.bitsnbites.eu/ to offset subtitles respective to time range of video extracted
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```py
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import re
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def adjust_timing(srt_file, haste_seconds):
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with open(srt_file, 'r') as file:
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content = file.readlines()
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adjusted_content = []
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for line in content:
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# Match timestamps
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if re.match(r'\d\d:\d\d:\d\d,\d{3} --> \d\d:\d\d:\d\d,\d{3}', line):
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start, end = line.split(' --> ')
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# Adjust both start and end times
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new_start = adjust_time(start, haste_seconds)
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new_end = adjust_time(end.strip(), haste_seconds)
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adjusted_content.append(f"{new_start} --> {new_end}\n")
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else:
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adjusted_content.append(line)
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with open('adjusted_subtitles.srt', 'w') as file:
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file.writelines(adjusted_content)
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def adjust_time(timestamp, haste_seconds):
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hours, minutes, seconds = map(float, re.split('[:,]', timestamp))
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total_seconds = hours * 3600 + minutes * 60 + seconds - haste_seconds
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if total_seconds < 0:
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total_seconds = 0 # Prevent negative timestamps
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new_hours = int(total_seconds // 3600)
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new_minutes = int((total_seconds % 3600) // 60)
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new_seconds = total_seconds % 60
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return f"{int(new_hours):02}:{int(new_minutes):02}:{new_seconds:06.3f}".replace('.', ',')
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adjust_timing('subtitles.srt', 300) # Hasten by 5 minutes (300 seconds)
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```
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- then extract video without subtitle like before then merge subtitle
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`ffmpeg -i input.mkv -ss 00:35:18.00 -t 50 -crf 20 -map 0:v:0 -map 0:a:0 recorded1.mp4`
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and
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`ffmpeg -i recorded1.mp4 -i subtitles-resync.srt -c copy -c:s mov_text outfile.mp4`
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and here this outfile.mp4 is desired file with extract video,audio and subtitles
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- convert video to audio
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`ffmpeg -i video.mp4 -b:a 192K -vn music.mp3` or `ffmpeg -i video.mp4 -vn music.mp3`
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here `-vn` means no video
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`-b:a 192K` : to target audio stream to tell it for 192k bitrate
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for converting all videos in folder to audio
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```bash
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for arg in * ; do
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ffmpeg -i "${arg}" -vn "${arg%%.*}.mp3"
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done
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```
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** get information about multimedia file**
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`ffprobe -i input.mp4`
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merging all videos
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https://www.mux.com/articles/stitch-multiple-videos-together-with-ffmpeg
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- create `inputs.txt` file and add the videos to be merged
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```txt
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file 'video1.mp4'
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file 'video2.mp4'
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file 'video3.mp4'
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```
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- then simply run this `ffmpeg -f concat -safe 0 -i inputs.txt -c copy output.mp4`
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`-f concat`: Specifies the concatenation format.
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`-safe 0`: Prevents file path errors if your filenames use relative or absolute paths.
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`-c copy`: Copies the video and audio streams directly without re-encoding, preserving 100% quality.
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**Method 2: Different Formats (Requires Re-encoding)**
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If your clips have different resolutions, frame rates, or codecs, you must use a Complex Filtergraph. This re-encodes the segments so they blend smoothly into a single unified format. [2, 8]
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Run this single command to merge two mismatched files: [9, 10, 11]
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`ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[0:v][0:a][1:v][1:a] concat=n=2:v=1:a=1 [v][a]" -map "[v]" -map "[a]" output.mp4`
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or
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`ffmpeg -i video_480p.mp4 -i video_720p.mp4 -filter_complex \
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"[0:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2[v0]; \
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[v0][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]" \
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-map "[v]" -map "[a]" -c:v libx264 -crf 23 -c:a aac final_output.mp4`
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* -i video1.mp4 -i video2.mp4: Specifies the input files sequentially.
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* [0:v][0:a][1:v][1:a]: Tells FFmpeg to extract the video and audio streams from input 0 (first file) and input 1 (second file).
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* concat=n=2:v=1:a=1: Combines the 2 input segments (n=2) into 1 output video stream (v=1) and 1 output audio stream (a=1).
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* -map "[v]" -map "[a]": Maps the newly joined streams to the final output file. [8, 9, 12]
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or if only 1 file is being different then only convert that one like others
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480 one converted to like of 720p one here
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`ffmpeg -i video_480p.mp4 -i video_720p.mp4 -filter_complex \
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"[0:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2[v]" \
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-map "[v]" -map 0:a -c:v libx264 -c:a aac converted_480p.mp4`
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then later merge them with others. though this will work if they were using those libx264 and aac audio. to be more safer some manual work like finding audio and video encoding via ffprobe. so for the witcher 3 recorded videos it was
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` Video: h264 (Main) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], 10006 kb/s, 28.91 fps, 60 tbr, 30k tbn (default)`
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and to convert 480p ones to witcher one
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`ffmpeg -i video_480p.mp4 -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2" -r 28.91 -c:v libx264 -profile:v main -c:a copy converted_480p.mp4`
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