feat(hub): move about in a film, and pick it up where it was left

Clicking the scrubber now restarts the stream there. A seek inside what is
already buffered never reaches the node. Dragging is debounced at 350 ms,
because `seeking` fires continuously and each one acted on kills an ffmpeg and
spawns another.

`SourceBuffer.mode` changes from 'sequence' to 'segments', and each stream sets
`timestampOffset` to where the node says it started — otherwise a stream
beginning at forty minutes is buffered at zero and the scrubber lies about
everything. Proved in Chrome before any of it was written: abort, remove, offset
600, append, and playback resumes at 600 with `readyState` 4.

A seek makes the buffer discontinuous, and everything reading `buffered` then
has to mean a particular range. "The last one" stops being "the one playing":
the read-ahead would report a full buffer across a gap while the player starves,
and the eviction would take out everything between the first range and the
playhead, including what is showing. Both work from the range around the
playhead now. `reinitAt` also clears the buffer outright rather than keeping two
ranges, and calls `abort()` first — ffmpeg was killed mid-fragment, so the
parser holds half of one and the next header would land on top of it.

The position is kept in localStorage, per file: no protocol, no storage anyone
else has to keep, and nothing new learns what you watch. Not below thirty
seconds, not past 97% of the film, and a pill offers the beginning back.

Two things this had to get right and did not at first, both found by running it
rather than reading it. Between asking for a seek and its `stream_init`,
everything on the channel belongs to the film being left — same file, so
`file_id` cannot separate them, but ordering can. And a segment that arrived is
no longer in flight whatever is then done with it: discarding one before
decrementing the window leaked a slot every time, and `reinitAt` is
asynchronous, so a whole window could arrive while it waited. The player then
believed eight segments were in flight, granted nothing further, and the node
waited for credit that could not come — a race, which is why the same seek
worked twice and hung on the third.

10 files changed, 20 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
index f045243..15401bf 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
@@ -121,6 +121,8 @@ export default {
   // Video player
   'video.loading': '{name} wird geladen …',
   'video.buffering': 'Wird gepuffert …',
+  'video.resumed_at': "Fortgesetzt bei {time}",
+  'video.from_start': "Von vorn beginnen",
   'video.close': 'Schließen (Esc)',
   'preview.pdf_fallback': 'Dieser Browser zeigt das PDF nicht direkt an. Laden Sie es '
     + 'stattdessen herunter — entschlüsselt wurde es ohnehin hier.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
index 25c1f6c..a98eb1a 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
@@ -120,6 +120,8 @@ export default {
   // Video player
   'video.loading': 'Loading {name}...',
   'video.buffering': 'Buffering...',
+  'video.resumed_at': "Resumed at {time}",
+  'video.from_start': "Start from the beginning",
   'video.close': 'Close (Esc)',
   'preview.pdf_fallback': 'This browser will not display the PDF inline. Download it instead — it was decrypted here either way.',
   'group.upload_indexing': 'indexing…',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
index 0799ec5..596d952 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
@@ -119,6 +119,8 @@ export default {
   // Video player
   'video.loading': 'Cargando {name}...',
   'video.buffering': 'Almacenando en búfer...',
+  'video.resumed_at': "Reanudado en {time}",
+  'video.from_start': "Empezar desde el principio",
   'video.close': 'Cerrar (Esc)',
   'preview.pdf_fallback': 'Este navegador no mostrará el PDF integrado. Descárguelo '
     + 'en su lugar — en cualquier caso se descifró aquí.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
index 32d0461..61dc99e 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
@@ -120,6 +120,8 @@ export default {
   // Video player
   'video.loading': 'Chargement de {name}...',
   'video.buffering': 'Mise en mémoire tampon...',
+  'video.resumed_at': "Reprise à {time}",
+  'video.from_start': "Reprendre depuis le début",
   'video.close': 'Fermer (Échap)',
   'preview.pdf_fallback': 'Ce navigateur n’affichera pas le PDF directement. '
     + 'Téléchargez-le plutôt — il a été déchiffré ici dans les deux cas.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
index 32d7922..6693115 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
@@ -120,6 +120,8 @@ export default {
   // Video player
   'video.loading': 'Caricamento di {name}...',
   'video.buffering': 'Buffering in corso...',
+  'video.resumed_at': "Ripreso da {time}",
+  'video.from_start': "Riparti dall'inizio",
   'video.close': 'Chiudi (Esc)',
   'preview.pdf_fallback': 'Questo browser non mostrerà il PDF nella pagina. Lo scarichi '
     + 'invece — in ogni caso è stato decifrato qui.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
index 0adc51c..8e18a19 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
@@ -117,6 +117,8 @@ export default {
   // Video player
   'video.loading': '{name} を読み込んでいます…',
   'video.buffering': 'バッファリング中…',
+  'video.resumed_at': "{time} から再開しました",
+  'video.from_start': "最初から再生する",
   'video.close': '閉じる（Esc）',
   'preview.pdf_fallback': 'このブラウザーはページ内に PDF を表示しません。'
     + 'ダウンロードしてご覧ください。いずれにせよ復号はここで行われています。',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
index 947724f..6fd9220 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
@@ -121,6 +121,8 @@ export default {
   // Video player
   'video.loading': '{name} wordt geladen...',
   'video.buffering': 'Bezig met bufferen...',
+  'video.resumed_at': "Hervat op {time}",
+  'video.from_start': "Vanaf het begin afspelen",
   'video.close': 'Sluiten (Esc)',
   'preview.pdf_fallback': 'Deze browser toont de PDF niet in de pagina zelf. Download '
     + 'hem in plaats daarvan — ontsleuteld werd hij hoe dan ook hier.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
index 687b93b..81f0139 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
@@ -126,6 +126,8 @@ export default {
   // Video player
   'video.loading': 'Wczytywanie {name}...',
   'video.buffering': 'Buforowanie...',
+  'video.resumed_at': "Wznowiono od {time}",
+  'video.from_start': "Odtwórz od początku",
   'video.close': 'Zamknij (Esc)',
   'preview.pdf_fallback': 'Ta przeglądarka nie wyświetli pliku PDF na stronie. Proszę '
     + 'go pobrać — i tak został odszyfrowany tutaj.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
index 56bfbdd..a2f41af 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
@@ -121,6 +121,8 @@ export default {
   // Video player
   'video.loading': 'Carregando {name}...',
   'video.buffering': 'Armazenando em buffer...',
+  'video.resumed_at': "Retomado em {time}",
+  'video.from_start': "Começar do início",
   'video.close': 'Fechar (Esc)',
   'preview.pdf_fallback': 'Este navegador não exibirá o PDF na própria página. Baixe '
     + 'o arquivo — de todo modo ele foi descriptografado aqui.',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
index 40a40a4..86c7580 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
@@ -115,6 +115,8 @@ export default {
   // Video player
   'video.loading': '正在加载 {name}…',
   'video.buffering': '正在缓冲…',
+  'video.resumed_at': "已从 {time} 继续播放",
+  'video.from_start': "从头开始播放",
   'video.close': '关闭（Esc）',
   'preview.pdf_fallback': '此浏览器不会在页面内显示该 PDF。请改为下载——无论如何它都已在本地解密。',
   'group.upload_indexing': '建立索引中…',