fix(playback): drop default_base_moof from progressive remux (Tizen native player)

[JonahMMay]

Progressive fMP4 remuxes don't play on Samsung Tizen's native player (capi-media-player, used by the Prairie Tizen app). The player can't follow moof-relative tfhd offsets (default_base_moof): it plays the first fragment, then stalls with no audio and reports "Not supported audio codec but video can be played". Every Tizen remux failed this way, and failure recovery then fell through to an HDR encode that has no recipe.

Found with Iron Man (HEVC Dolby Vision Profile 8 + TrueHD 7.1 Atmos only), which has to be remuxed for its audio.

Change

• Progressive remux -movflags changes from frag_keyframe+delay_moov+default_base_moof to frag_keyframe+delay_moov. delay_moov stays, for copied E-AC-3/Atmos.
• New test TestBuildRemuxArgsOmitsDefaultBaseMoof.
• New prairie-invariants.txt entry, so an upstream sync can't restore the flag unnoticed.

Why it's safe for other clients

The progressive remux is a single byte stream, not MSE/CMAF segments, so explicit base data offsets are correct for it. Browser <video> (the web player consumes server_remux_progressive through <video src>, not MSE), Media3's fragmented MP4 extractor, and AVFoundation all read explicit offsets. HLS segments are produced by ffmpeg's HLS muxer and are unaffected.

Verification

On a QN700B (Tizen 6.5), clips of the Iron Man source, each 45 s from 0:00, piped through ffmpeg exactly as buildRemuxArgsWithAudioV3 builds them:

Variant	Result
Server recipe as-is (DV8 hev1, AAC 5.1, default_base_moof)	Freezes at ~8 s, no sound
Same with DV stripped (hvc1)	Freezes at ~8 s, no sound
With default_base_moof, E-AC-3 instead of AAC	Freezes at ~9 s
With default_base_moof, 2 s fragments	Fails
Server recipe with default_base_moof removed (DV8 hev1, AAC 5.1)	Plays
Without default_base_moof, DV stripped	Plays
empty_moov, without default_base_moof	Plays

Go isn't installed on the machine this was made on, so the unit tests are left to CI. The invariant check passes on an LF-normalized checkout (24/24).

Related, not in this PR

The 2026-08-28 upstream sync (#174) also reverted #153 ("choose the remux container instead of always writing MP4"). HandleStream passes a literal "mp4" again, and movflags are no longer MP4-only. Iron Man doesn't need that fix: its TrueHD must be re-encoded, and Matroska with AAC didn't play on the TV. It is still a regression worth restoring separately, with an invariant.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Updated fragmented MP4 playback output to avoid a setting associated with reported playback issues on Samsung Tizen devices.
  • Progressive remux output no longer includes the default_base_moof flag.

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Reviewing files that changed from the base of the PR and between 6212fe5 and b4955c1.

📒 Files selected for processing (3)

• internal/playback/remux.go
• internal/playback/remux_dv_test.go
• scripts/prairie-invariants.txt

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