wiki/docs/media/index.md

# Media (General)

## Audio

### Split file with cue sheet and use filename from cue sheet

    :::shell
    shnsplit -D -f file.cue -t "%n %t" -o "flac flac -8 -o %f -" file.flac

To directly encode to opuus:

    :::shell
    shnsplit -D -f file.cue -t "%n %t" -o "cust ext=opus opusenc --bitrate=160k - %f" file.flac

### Remove all tags except MusicBrainz tags from flac files

    :::shell
    for i in *.flac; do tags=$(metaflac --export-tags-to=- $i | grep -E '^MUSICBRAINZ_'); metaflac --remove-all-tags $i; metaflac --import-tags-from=- $i <<< $tags; done

### Downmix 5.1/7.1 to 2.0

    :::shell
    mpv --oac=flac --audio-channels=stereo --oacopts=compression_level=0 --o=outfile.flac infile.flac

### Record pulseaudio device to flac

    :::shell
    parec [ -d DEVICE ] | flac --endian=little --channels=2 --bps=16 --sample-rate=48000 --sign=signed -o foo.flac -

### Copy Matroska Chapters to Opus

Requires the metadata to fit in one ogg page (so no cover art :().

    :::shell
    mkvextract file.mka chapters | xq -r 'def pad: tostring | (3 - length) as $l | ("0" * $l)[:$l] + .; [[.Chapters.EditionEntry.ChapterAtom[] | {start: .ChapterTimeStart, name: .ChapterDisplay.ChapterString}] | to_entries[] | "CHAPTER\(.key|pad)=\(.value.start)\nCHAPTER\(.key|pad)NAME=\(.value.name)"] | join("\n")' | opustags -i -S file.opus

## Video

### Copy DVD stream to file [with dvd already copied to local directory]

    :::shell
    mpv --stream-dump=1.mkv dvd://1 [--dvd-device path/to/dvd]

## Images

### Apply EXIF rotation to JPEG images

Requires `jhead` and `jpegtran`.

    :::shell
    nix shell nixpkgs#jhead nixpkgs#libjpeg.bin
    jhead -ft -autorot *.JPG

## MKV

### Fix mimetype of font attachments

Some matroska files have the mimetype for font attachment for fonts set to
`application/octet-strem`.

    :::shell
     mkvpropedit --attachment-mime-type font/sfnt --update-attachment mime-type:application/octet-stream file.mkv

## FFmpeg

### Create color timeline image from video

    :::shell
    (infile=in.mkv; outfile=out.png; rows=320; width=1920; height=1080; ffmpeg -i $infile -vf tblend=all_mode=average,fps=${rows}/$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 $infile),scale=1:1,scale=${width}/${rows}:${height},setsar=1,tile=${rows}x1 -frames:v 1 $outfile)

### Show duration of file in seconds

    :::shell
    ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 file.mkv

### Remove EIA-608 subtitles from video bitstream

([source](https://stackoverflow.com/a/51439554))

    :::shell
    ffmpeg -i infile.mkv -c copy -bsf:v "filter_units=remove_types=6" outfile.mkv

## QP file

replace 24/1.001 with framerate

    :::shell
    ffprobe -i infile.mkv -print_format json -show_chapters -loglevel error | jq -r '.chapters[].start / 1000000000 * 24/1.001 | round | tostring + " I"' >> foo.qp

## Manga

### Convert greyscale images to actuual greyscale

For some reasons, many releases encode greyscale manga pages as yuv420. Sadly,
the chroma layers are not completely empty but include some (almost invisible)
noise. This fixes that for lower battery comsumption, a really small file size
gain and just because it seems right.

This only works for pages with the same size (image2/ffmpeg limitation), but
releases suffering from this mostly fulfill this requirement.

**WARNING**: This uses some heuristics (SSIM > 98) to determine if a page is
greyscale. This may not work all the time (it did for me though). Please verify
if all converted images actually are greyscale.

    :::shell
    ffmpeg -loglevel error -f lavfi -i "movie=%03d.jpg:f=image2,split=2[orig][in2];[in2]extractplanes=y[grey];[orig][grey]ssim=-" -f null - >> ssim
    while read frame;do (( $(cut -d' ' -f5 <<< $frame | cut -c 7-8) < 98 )) || {file=$(printf "%03d.jpg\n" $(cut -d' ' -f1 <<< $frame|cut -d: -f2)); echo $file; jpegtran -copy none -optimize -grayscale -outfile $file $file}; done < ssim
    jpegoptim -s *.jpg
    exiftool -overwrite_original -all= *.jpg

    # print all converted images for verification
    grep -E 'All:0.(9[0-8]|[0-8][0-9])' ssim


### Merge page spreads to single page

Use function `merge_pages right-page left-page` (without .jpg). Result will be
written to left-page-right-page.jpg`.

    :::shell
    function merge_pages() {
        convert ${2}.jpg ${1}.jpg +append ${1}-${2}.jpg
        exiftool -overwrite_original -all= ${1}-${2}.jpg
    }

    # remove single pages
    mkdir single_pages
    for i in ???-???.jpg;do mv $(cut -d- -f1 <<< $i).jpg $(cut -d- -f2 <<< $i) single_pages;done

## mpv

### View thumbnails generated by [mpv-gallery-view](https://github.com/occivink/mpv-gallery-view)

    :::shell
    mpv --pause --demuxer=rawvideo --demuxer-rawvideo-mp-format=bgra --demuxer-rawvideo-w=288 --demuxer-rawvideo-h=162 FILE

Convert to tiles

    :::shell
    ffmpeg -codec:v rawvideo -pixel_format bgra -video_size 288:162 -f image2 -pattern_type glob -i '*' -vf tile=layout=10x10 tile-%04d.png

## Download

### Bilibili live recording

    :::shell
    curl 'https://api.live.bilibili.com/xlive/web-room/v1/record/getLiveRecordUrl?rid=R1sx411c7Xn&platform=html5'|jq -r '.data.list | map(.url) | to_entries[] | .value + "\n  out=" + (.key|tostring) + ".flv"' | aria2c --auto-file-renaming=false -x 16 -j 10 -i -
    mkvmerge '[' $(find . -name '*.flv'|sort -V) ']' -o merge.mkv

## PDF

### Downsample bitmap PDF

Useful for sending large 300/600 dpi scans as e-mail. Change `pdfimage32` to
`pdfimage8` for greyscale, `300` to the input DPI and `DownScaleFactor` to the
desired downscaling. For some reason fails when setting compression to JPEG.

    :::shell
    gs -sDEVICE=pdfimage24 -r300 -dDownScaleFactor=2 -o downscaled.pdf document.pdf

Imagemagick supports JPEG. Set your desired output density and JPEG quality.

    :::shell
    convert -density 300 -compress jpeg -quality 80 document.pdf downscaled.pdf

## Screen sharing

Since there is no good support for WebRTC screensharing with wayland, a virtual
webcam device can be used.

    :::shell
    sudo modprobe v4l2loopback exclusive_caps=1 card_label=screensharing # only has to be done once
    wf-recorder --muxer=v4l2 --codec=rawvideo --file=/dev/video2 -x yuv420p # adjust /dev/video2 to the actual device

To remove the virtual webcam device run `sudo modprobe -r v4l2loopback`