ffmpeg-video-editing

name	ffmpeg-video-editing
description	FFmpeg video editing patterns for creator workflows — silence removal, caption burning, aspect ratio conversion, clip extraction, intro/outro concatenation, and media inspection. Use when user says "edit video", "remove silence", "burn captions", "extract clip", "concat intro", "aspect ratio", "ffprobe", "caption style", "subtitle filter", "silence detect", or any FFmpeg video editing operation.

FFmpeg Video Editing Skill

Canonical FFmpeg patterns and proven defaults for a reusable video production pipeline. All video editing agents use these commands and settings as their source of truth.

Media Inspection (ffprobe)

ffprobe -v quiet -print_format json -show_format -show_streams "input.mp4"

Returns: duration, resolution, codec, bitrate, audio channels, aspect ratio.

Silence Detection

ffmpeg -i "input.mp4" -af "silencedetect=noise=-30dB:d=0.5" -f null - 2>&1

Defaults:

• Threshold: -30dB (captures natural breathing pauses)
• Minimum duration: 0.5s (catches genuine dead air, not brief pauses)
• Parse output for silence_start and silence_end lines

Rules:

• Add 50ms padding on each side when cutting to avoid clipping words
• Don't remove silence shorter than 0.5s — it clips speech beginnings

Silence Removal (Concat Method)

1. Parse silencedetect output → identify "keep" segments (non-silent)
2. Extract each keep-segment:

ffmpeg -y -ss [start] -i "input.mp4" -to [duration] -c copy "segment_N.mp4"

3. Create concat file (segments.txt):

file 'segment_1.mp4'
file 'segment_2.mp4'
file 'segment_3.mp4'

4. Concatenate:

ffmpeg -y -f concat -safe 0 -i segments.txt -c copy "tight_edit.mp4"

Caption Burning (ASS/SRT Subtitles)

⚠️ Windows Path Critical Issue

On Windows, the subtitles filter CANNOT handle absolute paths with colons (C:\). MUST cd into the directory and use relative filenames.

cd "C:\path\to\output\dir"
ffmpeg -y -i "input.mp4" -vf "subtitles=captions.srt:force_style='FontName=Arial Bold,FontSize=21,PrimaryColour=&H00FFFFFF,OutlineColour=&H00000000,Outline=3,Shadow=1,Alignment=2,MarginV=25'" -c:v libx264 -preset fast -crf 18 -c:a copy "captioned.mp4"

Default Caption Style

Setting	Value	Notes
Font	Arial Bold	Always bold
FontSize	21	NEVER >24 for 720p vertical. 36 is TOO BIG.
PrimaryColour	&H00FFFFFF	White text
OutlineColour	&H00000000	Black outline
Outline	3	Thick enough for readability
Shadow	1	Subtle drop shadow
Alignment	2	Bottom-center
MarginV	25	Minimum. Higher = text moves UP from bottom edge.

MarginV Direction Rule (CRITICAL)

Higher MarginV values push text UP from the bottom edge, NOT down.

• MarginV=25 → captions near the bottom ✅
• MarginV=160 → text pushed up into speaker's face ❌

Platform-Specific Caption Placement

Platform	Aspect	Safe Zone
TikTok/Reels/Shorts	9:16	Captions within middle 70% vertically
Instagram Feed	1:1	More forgiving, ensure no face overlap
YouTube Main	16:9	Traditional subtitle position (bottom 10%)

Frame-Accurate Clip Extraction

# Fast seek + precise cut
ffmpeg -y -ss 00:01:30 -i "input.mp4" -to 00:00:60 -c:v libx264 -c:a aac -preset fast "output_clip.mp4"

Rules:

• -ss before -i = fast seek (input seeking)
• -to specifies duration from the seek point, NOT absolute timestamp
• Always re-encode clips (-c:v libx264 -c:a aac) for frame accuracy

Aspect Ratio Conversion

16:9 → 9:16 (Center Crop for Vertical)

ffmpeg -y -i "input.mp4" -vf "crop=ih*9/16:ih,scale=1080:1920" -c:v libx264 -c:a aac "vertical.mp4"

16:9 → 1:1 (Square)

ffmpeg -y -i "input.mp4" -vf "crop=ih:ih,scale=1080:1080" -c:v libx264 -c:a aac "square.mp4"

16:9 → 4:5 (Feed)

ffmpeg -y -i "input.mp4" -vf "crop=ih*4/5:ih,scale=1080:1350" -c:v libx264 -c:a aac "feed.mp4"

Intro/Outro Concatenation

Asset Selection (by aspect ratio)

Aspect	Intro	Outro
16:9	{{VIDEO_ASSET_DIR}}\intro.mp4	{{VIDEO_ASSET_DIR}}\outro.mp4
9:16	{{VIDEO_ASSET_DIR}}\intro-portrait.mp4	{{VIDEO_ASSET_DIR}}\outro-portrait.mp4
1:1	{{VIDEO_ASSET_DIR}}\intro-square.mp4	{{VIDEO_ASSET_DIR}}\outro-square.mp4
4:5	{{VIDEO_ASSET_DIR}}\intro-feed.mp4	{{VIDEO_ASSET_DIR}}\outro-feed.mp4

Duration Rules

Video Type	Intro?	Outro?
Main (>60s)	✅	✅
Shorts (<60s)	❌	✅
Medium (60s-5min)	✅	✅

Concat Command (Same Codec)

# Create filelist.txt
@"
file '{{VIDEO_ASSET_DIR}}\intro-portrait.mp4'
file 'captioned-final.mp4'
file '{{VIDEO_ASSET_DIR}}\outro-portrait.mp4'
"@ | Set-Content filelist.txt

ffmpeg -y -f concat -safe 0 -i filelist.txt -c copy "output-with-bumpers.mp4"

⚠️ Time_Base Mismatch Fix (CRITICAL)

If caption-burned video has different time_base than bumpers (common after libx264 re-encode), concat with -c copy produces corrupt output (3hr file from 4min source).

Solution: ALWAYS re-encode during concat:

ffmpeg -y -f concat -safe 0 -i filelist.txt -c:v libx264 -preset fast -crf 18 -c:a aac "output-with-bumpers.mp4"

Validation: After concat, verify output duration ≈ sum of input durations (±2s). If wildly off → re-encode.

Transcription (faster-whisper)

from faster_whisper import WhisperModel

model = WhisperModel("base", device="cpu", compute_type="int8")
segments, info = model.transcribe("input.mp4", language="en", word_timestamps=True)

# Generate SRT
for i, segment in enumerate(segments, 1):
    print(f"{i}")
    print(f"{format_time(segment.start)} --> {format_time(segment.end)}")
    print(f"{segment.text.strip()}")
    print()

Model Selection

Model	Speed	Quality	Use When
tiny	~10x realtime	Lower	Quick preview
base	~5x realtime	Good	Default for speed
small	~2x realtime	Better	Final captions
medium	~0.5x realtime	High	Accuracy critical
large-v3	Slow (GPU needed)	Best	Premium content

Default: base for speed. Use small for final published captions.

Telegram Video Delivery

The built-in telegram_send_photo does NOT work for video files. Use Telegram Bot API sendVideo endpoint directly:

$botToken = (Get-Content .env | Where-Object { $_ -match '^TELEGRAM_BOT_TOKEN=' }) -replace 'TELEGRAM_BOT_TOKEN=',''
curl.exe -X POST "https://api.telegram.org/bot$botToken/sendVideo" -F "chat_id={{TELEGRAM_CHAT_ID}}" -F "video=@output.mp4" -F "caption=✅ Your edited video is ready!"

Supports files up to 50MB.

Common Pitfalls

• ❌ Using FontSize=36 (covers speaker's face on vertical video)
• ❌ Using absolute Windows paths in subtitles filter (breaks on colon)
• ❌ Using -c copy for concat when codecs/time_bases differ
• ❌ Forgetting 50ms padding on silence removal (clips words)
• ❌ Using telegram_send_photo for video files
• ❌ Using MarginV=160+ (pushes captions into face area)