Entry 22

The opening's sound: the drive drops the repeated audio sectors

2026-10-1524maudiovideotooling

The opening's audio was badly wrong in the port. 5643 of OPEN.BIN's sectors are XA audio for file 1, channel 1: four in five of the stream, where a stereo 37.8 kHz channel at double speed needs one in eight. Decoded end to end they make 300 s of sound for a 47 s scene.

The search went through a few wrong turns:

• Successor tests on the decoded audio and a pitch estimate (median about 620 Hz at 37.8 kHz) said the audio was one continuous, natural-pitch stream.
• The characters' motion per frame looked slow for 30 frames a second.
• The end title card (frames 1184-1412) would last 49 s if the picture followed the audio.

The answer was in the bytes: 535 of the first 634 neighbouring audio sectors are identical. The encoder repeats each sector to fill the bandwidth, and the CD-ROM controller's decoder drops any sector that arrives while its output still holds more than a few frames. It has no flow control, and DuckStation's source models it the same way. The continuity tests had been comparing sectors with their own copies.

movie::XaPlayer models it: a sector arriving at its disc time (1/150 s each) is decoded only if no more than 10 frames are queued, and a dropped sector leaves the ADPCM history alone. The opening now plays 882 sectors, 47.1 s, every distinct sector once. The movies go through the same path (their one in eight never drops).

Along the way the oracle got RUGRATS_NO_PAD. With the SIO model and no pad the game shows "No Controller"; the switch also leaves libpad's handler out, which gives the old path straight to the opening. The GPU trace now covers lines and colours and any number of frames. In the oracle's opening the milk from Tommy's bottle turned out to be about four semi-transparent gouraud triangles a frame (blend mode 3, grey 166), built by the C model path's face emitters from a face flag. The port has no such object yet.

retro_rt is now 719d0fa (rrt-dis with the lifting IR and the decompiler).