52 lines
2.4 KiB
Markdown
52 lines
2.4 KiB
Markdown
# Goal of the script
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Remove ads from TV recordings with optimal cuts with single video frame precision.
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When I record a movie on TV, I sometimes wish to archive the movie on my NAS.
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In that case, I want to remove (at least) the beginning and the end of the recording
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if the movie was broadcast on a advertisment free channel, or even worse I may
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have to split it in numerous parts so as to remove the advertisments.
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And I do not want to reencode the entire movie since it's a really slow process (on my NAS)
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and the movie is already broadcast using H264 (DVB-T).
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Doing this by hand is really painful, because most tools like ffmpeg, or mkvmerge are only
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able to cut a movie (without reencoding) at a boundary within the video stream that corresponds
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to a reference frame (so called I-frames). These frames are only present roughly every 10-20 frames
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which corresponds to quite long duration (in the order of a second).
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I really want to cut the movie with a better precision. So I have written a Python script
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that leverages _ffmpeg_, _ffprobe_ and _mkvmerge_, _subvodocr_ to do the job with the required precision.
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# Parameters
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# How does it work ?
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The processing follows a quite long pipeline:
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1. The original .ts file is first transformed into an .mp4 file using _ffmpeg_ to correct timestamps:
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2. The .mp4 is then transformed into a Matroska container (which is the default container) still using _ffmpeg_:
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3. Then the movie is then cut using the indications passed as parameters. It is possible to give as many parts as needed.
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Each part is treated with the same algorithm.
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Trouver l'estampille de la trame 'I' la plus proche (mais postérieure) au début de la portion.
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Trouver l'estampille de la trame 'I' la plus proche (mais antérieure) à la fin de la portion.
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On a alors
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debut ----- trame --------- trame --------- fin.
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'B/P' 'B/P'* 'I' 'I' 'B/P'* 'B/P'
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Si la trame de début est déjà 'I', il n'y a rien à faire (idem pour la fin).
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Sinon on extrait les trames 'B' ou 'P' depuis le début jusqu'à la trame 'I' non incluse
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4. Then each part that have been previously obtained are merged using _mkvmerge_:
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5. The subtitles (image based) are then extracted using _mkvextract_:
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6. These images are then processed using _vobsubocr_ to create SRT files:
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7. The SRT files are then remuxed inside the Matroska container using _mkvmerge_:
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# How to determine where to cuts
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Use `mpv --osd-fractions --osd-level=3 ./movie.ts`
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