Control parts reference
Part of SABR in the extractor. Every non-media UMP part the server can send, with its part-type id, proto fields, and what it does. Field numbers are from each class's decode(); names past the obvious ones are reverse-engineered.
Pacing
SabrNextRequestPolicy — id 35
How and when to send the next follow-up.
| # | Field |
|---|---|
| 1 / 2 | target audio / video readahead (ms) |
| 3 | max time since last request (ms) |
| 4 | backoff before next request (ms) — the authoritative backoff |
| 5 / 6 | min audio / video readahead (ms) |
| 7 | playback cookie (also decoded into SabrPlaybackCookie) |
| 8 | videoId |
No request-number field; the URL rn is managed by the session. The cookie threads session state into the next request.
SabrPlaybackStartPolicy — id 47
Minimum readahead before starting / resuming, conditioned on bandwidth. Field 1 = start policies, field 2 = resume policies; each ReadaheadPolicy is {1 minBandwidthBytesPerSecond, 2 minReadaheadMs} ("below this bandwidth, buffer at least this much first").
SabrRequestCancellationPolicy — id 53
When in-flight requests should be cancelled. Carries a list of items, the only named sub-field is minReadaheadMs.
SabrPrewarmConnection — id 65
Connection prewarm hints. Decoded structurally for diagnostics only.
Protection
SabrStreamProtectionStatus — id 58
| # | Field |
|---|---|
| 1 | status (raw int) |
| 2 | maxRetries |
The status enum is not named in code, only a raw int. Per the project research: 1 = OK/attested (real media), 3 = protection required (no media, mint a PO token); 2 is intermediate. status >= 3 with no media is the PO-token boundary the session acts on.
Navigation
SabrRedirect — id 43
Field 1 = the new streaming URL. The session swaps serverAbrStreamingUrl and counts the hop (capped at 3/session).
SabrSeek — id 45
Server-initiated seek: {1 seekMediaTime, 2 seekMediaTimescale, 3 seekSource}. Real time = seekMediaTime / seekMediaTimescale.
SabrReloadPlayerResponse — id 46
The player response expired. Three nested levels, each field 1, down to a reloadPlaybackParamsToken string. The session re-fetches a fresh YoutubeSabrInfo and resumes in place (see the session driver).
Context
SabrContextUpdate — id 57
A keyed blob the client must echo back in the streamer context on later requests.
| # | Field |
|---|---|
| 1 | type (key id) |
| 2 | scope |
| 3 | value (bytes; decoded into SabrContextValue) |
| 4 | sendByDefault |
| 5 | writePolicy (1 = overwrite, 2 = keep existing) |
When echoed, only {1 type, 2 value} are re-encoded. SabrContextValue further decodes the value into a timing info (timestampMs, durationMs) and a content info (contentId, contentType), plus a signature length.
SabrContextSendingPolicy — id 59
Which context types to start / stop / discard sending: field 1 start, field 2 stop, field 3 discard (each a single or packed list of SabrContextUpdate.type ids).
Live
SabrLiveMetadata — id 31
| # | Field |
|---|---|
| 1 | broadcastId |
| 3 | headSequenceNumber (live edge; -1 if unknown) |
| 4 | headTimeMs |
| 5 | wallTimeMs |
| 6 | videoId |
| 8 | postLiveDvr (ended live, still DVR-seekable) |
| 12 / 13 | min seekable time ticks / timescale |
| 14 / 15 | max seekable time ticks / timescale |
Formats
SabrFormatInitializationMetadata— id 42: per-format init (endSegmentNumber, mimeType, init/index ranges, duration units/timescale). Drives the segment index.SabrSelectableFormats— id 51: the video/audioFormatIds the server will serve.SabrFormatSelectionConfig— id 37: itags + a resolution the server wants requested.
Misc
SabrError— id 44:{1 type (string), 2 code}. Fatal to the round.SabrSnackbarMessage— id 67:{1 id}, a user-facing message identifier.SabrRequestIdentifier— id 52: a server-issued token (field 1) tagging the round; summarized by length only, never printed.
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