feat(download): start real SABR download support

[Priveetee]

Fixes / continues InfinityLoop1308/PipePipe#2569

Context: #66 (comment)

Pairs with the extractor-side helper draft: InfinityLoop1308/PipePipeExtractor#79

Summary

This starts the real SABR download implementation.

I have something working locally now, but this is still draft. I will keep updating this PR while testing/fixing the remaining cases. Once it looks solid enough, I will ask for review.

Why

The old downloader cannot handle SABR as a normal URL.

SABR is a session, not a direct media file. So the download path needs to drive a YoutubeSabrSession, request the selected formats, collect init/media segments, write them in order, and mux the final result.

Since HLS also looks less reliable now, I think we need to start moving download toward real SABR support instead of only relying on temporary fallbacks.

What works locally right now

Tested on emulator:

https://www.youtube.com/watch?v=lLaRC7GkVR8

Selected stream:

AV1 480p SABR
itag 397

Audio:

AAC
itag 140

Result:

final MP4 generated successfully

ffprobe sees:

video: AV1 854x480, ~276s
audio: AAC, ~276s
size: ~15 MB

What changed

• Detect SABR streams/resources in the download flow
• Store SABR recovery info in the mission
• Route SABR missions to a dedicated SABR downloader
• Drive a SABR session for selected audio/video formats
• Write SABR init/media segments to temp files
• Handle delayed init segments
• Keep media segments ordered
• Handle SABR policy-only responses as retryable idle responses
• Remux the downloaded tracks with ffmpeg
• Clean SABR temp files with mission cleanup

Still not done

This is not merge-ready yet.

I still want to test/fix:

• VP9
• AVC1
• WebM + Opus
• audio-only
• cancel / restart
• longer videos
• ffmpeg failure cases
• retry limits around policy-only responses
• memory behavior
• cleanup temporary debug logs

Notes

Opening this as draft so the direction is visible early.

The base path works locally now, but I will continue updating it before asking for review.

[Priveetee]

@InfinityLoop1308 I think this one is ready for a first real review now.

I kept it as draft while testing because SABR download is a big change and I did not want to rush it. I pushed more fixes after the first draft, especially around single-track/audio-only init recovery and retry behavior.

What I tested on emulator:

• AV1 720p HFR download: ok, final MP4 with AV1 + AAC.
• VP9/WebM video+audio: ok.
• Opus audio-only: ok.
• Audio-only after a clean reinstall + SAF folder permission + overwrite: ok.
• Long video download, Big Buck Bunny 10m34: ok.
• Network cut/reconnect during download: ok, final file still valid.
• Force-stop during download, then resume from Downloads: ok.
• Temporary SABR work directory cleanup after success/retry/resume: ok.

I also tested a few different videos, not only one sample:

• lLaRC7GkVR8
• aqz-KE-bpKQ
• dQw4w9WgXcQ
• 3JZ_D3ELwOQ

I still would like you to test it too on your side, especially with formats/videos that usually hit SABR edge cases. I could not do the final physical-device run today because my Pixel was not visible in adb anymore, but emulator testing is now much better than before.

[InfinityLoop1308]

Really fast XD

quick test:

1. no progress (percent)
2. resume lose all the progress

[InfinityLoop1308]

and don't push yourself :) you can just take this one and I'll handle other bugs.
these days are really busy - we should all take a rest after 5.2.1 lol

[Priveetee]

@InfinityLoop1308 I pushed a small follow-up for these two points.

For the percent: SABR download was forcing unknownLength = true, so the UI could only show the indeterminate progress. Now, when nearLength is known, it keeps a normal length and the percent can be displayed.

For resume: this is still not real segment-level resume yet. SABR currently restarts the temp transfer, but now it keeps the previous visible progress as a floor. So on resume/retry it does not jump back to 0%; the restarted transfer catches up silently, then progress continues from there.

Build is still ok on my side with ./gradlew :app:assembleDebug -Px86 --no-build-cache --no-configuration-cache --no-daemon.

[Priveetee]

and don't push yourself :) you can just take this one and I'll handle other bugs.
these days are really busy - we should all take a rest after 5.2.1 lol

I’m fine, no worries :)

And np, honestly it’s a pleasure. I like coding when I come back from work or when I have some free time, I get more fun from coding than from doing other stuff :P