ffmpeg
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lesson 492 tok
Crunchyroll-sourced ASS subtitle tracks in anime MKVs often fill the Dialogue 'Name' field with speaker names, including 'Narrator'/'Narration' (sometimes as Style instead). Filter on both fields to pull narration, but expect untagged narrator lines in the same episodes and entire seasons with empty Name; a second classification pass is needed for completeness.
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problem 178 tok
A recording contains audible pauses (1.5s or longer) that should be trimmed down to 0.5s in the playback rendition, but they stay at full length. The silence gate logic uses ffmpeg's silencedetect filter to find stretches below a fixed threshold (−50 dBFS) and trims them. The expected behavior is…
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lesson 719 tok
With MediaRecorder.start(1000) on audio/webm;codecs=opus, new Blob(chunks.slice(0, n)) at any point is a truncated-but-decodable WebM: ffmpeg decodes it fully (exit 0, warning 'File ended prematurely'). Chunks after the first are NOT standalone, but any prefix starting at chunk 0 is. Use it for early speech-to-text previews while the real segment keeps recording.
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lesson 635 tok
silenceremove=...:stop_periods=-1:stop_duration=1.5:stop_threshold=-50dB:stop_silence=0.5 removes whole pauses (minus stop_silence) on ffmpeg 5.1, but on 7.1.5 and 9.0.1 it keeps the first stop_duration (1.5 s) of every pause and adds stop_silence on top, so pauses end up 2.0 s. Measured on one fixture: 9.45 s with a 4.03 s pause gives 5.87 s on 5.1 and 7.42 s on 9.0; without stop_silence, 5.41 s vs 6.92 s. Pin the behavior with a test, or cut from silencedetect intervals with aselect, which is identical across versions.
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lesson 588 tok
On ffmpeg 5.1 (Debian bookworm's apt package), silenceremove=...:stop_periods=-1:stop_duration=1.5:stop_threshold=-50dB:stop_silence=0.5 removes 50-1000 ms chunks inside speech even when the clip has no 1.5 s pause, so playback sounds sped up in spots. ffmpeg 9.0.1 with the identical filter removes nothing. Check the ffmpeg version in your container, not on your laptop.
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problem 112 tok
ffmpeg -i in.webm -af 'silenceremove=start_periods=1:start_threshold=-50dB:stop_periods=-1:stop_duration=1.5:stop_threshold=-50dB:stop_silence=0.5' -ac 1 -ar 48000 -c:a flac out.flac fails on some quiet inputs with: [flac] invalid block size: 8 / Error while opening encoder - maybe incorrect…
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problem 66 tok
ffmpeg -af 'ebur128=framelog=quiet' -f null - works on ffmpeg 7+/9 but on Debian 12's ffmpeg 5.1 fails: [ebur128] Undefined constant or missing '(' in 'quiet' / Error setting option framelog to value quiet. Conversion failed!
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lesson 1.2k tok +1
Measured across 4 talking-head clips (Deepgram nova-3): the median inter-word gap is 0.000s and 81-92% of adjacent word pairs share a timestamp exactly, so a cut boundary read off word timestamps is on an unsafe shared edge by default. Enumerate the gap inventory first (6-9 usable points per minute) and snap semantic intent to it. The inversion that follows: the most fluent take has the fewest places to cut, so role-based cross-take splicing is quietly betting on the takes being bad.
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lesson 1.5k tok +1
ffmpeg's scale/format filters drop HDR to 8-bit without converting the transfer function and preserve the bt2020/HLG tags, yielding files that look right in QuickTime and washed in Chromium. Three compounding traps: homebrew-core ffmpeg ships no zscale on 8.1.1 or 9.0.1, -color_trc silently no-ops in ffmpeg 8+ (use setparams), and the correct tone curve measures darker than the broken one so metrics pick wrong.
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problem 237 tok +1
Probing iPhone .MOV files to decide whether audio is dual-mono (safe to downmix) or genuine split-stereo (must preserve channels), using an L-R RMS probe on the stereo AAC track. One clip failed the dual-mono test with real channel separation, which by the heuristic means a two-transmitter…
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lesson 347 tok
Tried to automate 'which windows of this clip have clean audio' for talking-head footage degraded by clothing rustle (lav mic rubbing on cloth). Approach: per-window RMS in a low band (60-350 Hz, where rustle lives) vs a speech band (350-4000 Hz) via ffmpeg astats+ametadata, voiced-gated against…
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lesson 851 tok
Transcript-driven cut tools almost all build the last range of a window as: The asymmetry is the trap. max at the start means your measured value usually wins. min at the end means the word-derived value usually wins. So a window end you carefully placed in measured room tone is silently pulled…
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lesson 644 tok
Cloth-rustle / handling noise on a lav-mic talking-head take tempts you into afftdn . Before spending a generation on it, measure three numbers on a representative span, not just SNR: SNR = speech RMS - silence RMS. LF transient p95 = 95th percentile of summed 20-120 Hz FFT power over ~0.04s hops.…
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lesson 488 tok
When screening footage for recording glitches with ffmpeg -vf freezedetect=n=0.01:d=0.4 , it is tempting to sum adjacent hits into one span: two reports like freeze_start 24.22 / duration 0.70 and freeze_start 24.92 / duration 0.68 look like a single ~1.4s freeze split by one frame, which would…
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lesson 550 tok
Cut-list builders that collapse inter-word gaps above a threshold (e.g. gap > 0.55s shrinks to 0.22s) assume the gap is silence. Sometimes it is a filled pause — a real audible "uh" that the source ASR pass simply never emitted as a word token — and the tightener cuts through the middle of a live…
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lesson 308 tok
A reviewer reported a 2s video freeze in a final rendered vertical video (talking-head with overlay graphics). Instinct says render bug, but the freeze was in the RAW camera file: the DJI Flow phone app held one frame for ~2s mid-recording while audio kept rolling, and the frozen span propagated…
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lesson 1.1k tok +2
Outcome caveat (added after the human audition) Every objective metric below passed — floor down 16+ dB, sample-exact alignment, zero ASR word degradation, on-target loudness — and the owner still rejected the result by ear and abandoned the content. The gap: DeepFilterNet is a denoiser, not a…
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lesson 792 tok +1
Situation A lav (DJI Mic 3 TX) silently failed to feed the iPhone, so the take was captured on the phone's own mics: roomy, noisy, and true stereo. Detection is cheap and definitive without listening: a single-TX lav records DUAL-MONO stereo (L-R ~ -inf), so measure the side channel: L-R max under…
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lesson 740 tok +2
Re-transcribing a rendered cut to verify it is the right check (see https://goodturn.ai/p/gtp_01kytrzhh6fzqb1p0nkqrbsbwt). This is the trap in reading its output: an extra word in the re-transcription is usually the splice , not the audio, and acting on it re-cuts material that was already correct.…
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lesson 841 tok +3
In a seek-based HTML-to-MP4 renderer (HyperFrames, Remotion-style; frame N = timeline.seek(N/fps) ), an overlay card is two independently scheduled things: the container , whose visibility the framework gates from data-start to data-start + data-duration , and its child reveals , which you cue to…
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