Entry 6

The logo movies play in the port: STR, BS version 3, XA sound, the input module

2026-10-1410mvideoaudioformatinputtest

After the legal screen, main plays three movies, THQ, Nickelodeon and n-Space (movie_play(0..2, skippable), 0x8008b448), and the port now does too: frames decoded natively, the XA soundtrack through retro_rt's audio output, a button press skipping to the next logo.

Finding them

The oracle showed colour noise in the shape of the THQ logo: the movies are decoded at 24 bits and shown in the GPU's 24-bit display mode, which the oracle's screen grab read as 15-bit. With the mode bit (GP1 0x08 bit 4) modelled, the oracle shows them right. movie_play takes movie n from a table at 0x800bae4c of {frames, lba}; seven movies, the last the 1875-frame credits. None of the seven ...B.STR files is in it (docs/cut/b-movies.md).

Decoding, held to the original

A frame is the 2016-byte parts of its STR sectors (rugrats_data::movie). THQ_LOGO's frames are BS version 3: the DC as MPEG-1 codes it, a size from table B.12 (luma) or B.13 (chroma) and a difference from the last block of the same kind, kept per Cr, Cb and luma, in steps of 4. NICKLOGO's are version 2, and end with a DC of 0x1ff, which libpress takes as the end of the frame; the decoder read on into the padding and failed at bit 22026 of frame 1 until it did the same. The oracle's MDEC dumps cover the three logos: thq_logo_frames_decode_to_what_libpress_hands_the_mdec holds all 101 THQ frames to them by number, and the_logo_movies_decode_as_the_original_decodes_them holds all 345 frames the original decoded (it dropped 6 of 351) to the port's, word for word.

Pacing and the skip

The oracle shows the original sampling the pads (0x8001acc0) and asking for a skip (0x8001baf8 mode 0) about every 4 vertical blanks during a logo: a frame is shown when its sectors have arrived, about 10 sectors at 150 a second. The port reads the whole stream up front (a PC holds it easily) and shows frame k when its last sector would have arrived, decoding it then; the soundtrack is decoded with rrt's XA decoder and starts at its first sector's time. The skip is checked every other tick.

The input module is ported as the game keeps it: per port a 32-frame history of each of the 16 buttons, newest in bit 0, so "pressed" is the low two bits reading 01 (a_press_is_seen_for_one_frame). Its six controller maps (0x800b44ac) are not ported yet.

The oracle gained the BIOS pad driver (B0:12 InitPAD, B0:13 StartPAD) and --press F:BUTTON[:LEN] scripts, and --count ADDR to count calls per frame, which is how the pacing above was measured.