feat(tracks): download and mux stereoscopic 3D (MV-HEVC) video to MP4

Mark 3D from REQ-VIDEO-LAYOUT, DV profile 20 codecs or an lhvC box; mux with MP4Box, decrypt with mp4decrypt, skip FFmpeg repack, sample cut and hybrid; add {3d} and env MP4Box.

docs/reference/configuration/drm.md

@@ -187,6 +187,10 @@ service tag case-insensitively and uses the `default` entry as the fallback.
 
 unshackle decrypts HLS AES-128 ClearKey in-process and ignores this setting.
 
+unshackle decrypts a stereoscopic 3D (MV-HEVC) track with mp4decrypt whatever this setting says.
+shaka-packager refuses its Dolby Vision configuration (version 3), and before v3.5.0 it also drops
+the boxes of the second view.
+
 mp4decrypt finds a content key by the KID in the first `sinf` box of the track. When that box
 has no CENC `tenc` (for example, a PIFF `sinf` before the CENC one), unshackle also gives
 mp4decrypt the content key of that KID by track ID. When mp4decrypt copies a track through

docs/reference/configuration/output.md

@@ -40,7 +40,7 @@ folder-kind keys.
     `absolute`, `date`, `quality`, `resolution`, `source`, `tag`, `track_number`, `artist`,
     `album_artist`, `album`, `disc`, `track_total`, `disc_total`, `release_type`, `genre`,
     `explicit`, `isrc`, `upc`, `label`, `audio`, `audio_channels`, `audio_full`, `atmos`,
-    `dual`, `multi`, `dubbed`, `video`, `hdr`, `hfr`, `edition`, `repack`, `lang_tag`,
+    `dual`, `multi`, `dubbed`, `video`, `hdr`, `hfr`, `3d`, `edition`, `repack`, `lang_tag`,
     `title_type`.
 
 !!! warning "`{part?}` is already inside `{season_episode}`"
@@ -129,7 +129,7 @@ Rule semantics:
 - A value can be a scalar or a list. A list matches if **any** entry matches.
 - Comparison is case-insensitive string equality.
 - The keys of `when` are the filename template variables for the release itself:
-  `title_type`, `quality`, `resolution`, `source`, `video`, `hdr`, `hfr`, `audio`,
+  `title_type`, `quality`, `resolution`, `source`, `video`, `hdr`, `hfr`, `3d`, `audio`,
   `audio_channels`, `audio_full`, `atmos`, `dual`, `multi`, `dubbed`, `edition`, `repack`,
   and `lang_tag`. Only these are available. unshackle adds the title's own fields (`title`,
   `year`, `season`, `episode`, and so on) after it evaluates the rules, so a condition cannot

docs/reference/configuration/post-scripts.md

@@ -113,7 +113,7 @@ values.
 | `{year}` `{season}` `{episode}` `{episode_name}` | Season and episode are plain numbers (`1`, `5`) |
 | `{part}` | Part number of a split episode as a plain number (`1` for `Part.1`). Empty when the episode has no part |
 | `{season_episode}` `{absolute}` `{date}` | As in the filename template: `{season_episode}` keeps the part suffix (`S01E05.Part.1`) while `{episode}` drops it |
-| `{quality}` `{resolution}` `{hdr}` `{hfr}` `{vcodec}` `{acodec}` `{edition}` `{tag}` `{lang_tag}` | As in the filename template, for this file |
+| `{quality}` `{resolution}` `{hdr}` `{hfr}` `{3d}` `{vcodec}` `{acodec}` `{edition}` `{tag}` `{lang_tag}` | As in the filename template, for this file |
 | `{tmdb}` `{imdb}` `{tvdb}` | The tagging IDs in use, otherwise empty. See [Tagging IDs](#tagging-ids) |
 | `{error}` | Failure message. Empty on success |
 
@@ -132,7 +132,7 @@ Every variable from your `output_template` is available here as well, including
       music has none of them.
     - **The naming context renders it empty on purpose.** `{hdr}` is empty for an SDR
       file, because SDR is the absence of an HDR tag in a filename rather than a tag that
-      reads `SDR`. `{edition}`, `{atmos}`, `{multi}`, `{dual}` and `{hfr}` behave the same
+      reads `SDR`. `{edition}`, `{atmos}`, `{multi}`, `{dual}`, `{hfr}` and `{3d}` behave the same
       way. If your script needs the word `SDR`, derive it from an empty `{hdr}` yourself.
     - The post-script is a `failure` one. A failed download has no output file to read metadata
       from, so everything that comes from the output file is empty. See