Entry 49

The PSS movies: our own MPEG-2 decoder, exact against ffmpeg, played by the title

2026-09-23videoaudiotest

Filescrates/piney-mpegcrates/piney-data/src/pss.rscrates/piney-audio/src/lib.rscrates/piney-game/src/session.rsdocs/formats/pss.md

Until now the title's four movies counted as played (43), and the user asked why PSS never worked. A helper agent wrote the format and a decoder. I added the movie sound to piney-audio and the player to the runtime. The reference is the PSS page.

What the movies are

• Where they play. Only the title plays PSS: LogoMain calls ccDecodeMpeg four times (LOGO_B, LOGO_C, LOGO_H, OPENING). The desktop Audio screen's "movies" are not PSS. SimplePlayStream starts ccThExecuteStream, an in-engine STREAM/*.BIN cutscene, which is the stream port's job.
• The container. 16 KB MPEG-2 packs of four PES packets. Video is stream 0xE0. Audio is private stream 1 with the sub-header FF A0 00 ch, which is also what the game's demultiplexer keys on (_strmap).
• The video. 640 x 448 at 30 pictures a second, Main profile, all progressive frame pictures. The logos have 146, 180 and 151 pictures and OPENING has 2,771.
• The sound. Only OPENING has sound: 48 kHz stereo 16-bit PCM in the SPU2's own block layout (256 left samples, then 256 right). The game sends it untouched to core 0's sound-data input at volume 0x7fff, not scaled by the BGM volume. It has no ADPCM.

The decoder

piney-mpeg is ours, written from the MPEG-2 standard:

• the bitstream reader and VLC tables;
• a "simple IDCT" in ffmpeg's integer arithmetic;
• the IPU's colour conversion, whose alpha is 0x80.

Movie::next_frame gives each picture as the frame setImageTag draws: a PSMCT32 upload and one sprite over the screen.

Playing them

Demo asks with Request::Movie and waits for the movie before its next step. The session plays it as ccDecodeMpeg does:

• the first picture and the sound start together;
• each picture shows for two frames (the game paces by vblank and ignores the time stamps);
• OK, cancel or START (the save's assignPADok and assignPADcancel, and 0x800) stop it once twelve pictures are decoded. The title then skips the remaining logos and the opening.

Audio::movie_stream and movie_stream_stop are audioDecStart and audioDecReset.

The texture cache in piney-gs evicted nothing until 4,096 textures were cached. For the opening that meant about 3 GB of pictures; the fix is cee9693.

Checked

• The decoder. piney-mpeg's ffmpeg tests decode all four files both ways: 3,248 of 3,248 pictures are exact, the same count in the same order. The integer IDCT passes IEEE 1180.
• Against another IDCT. Against ffmpeg's -idct int, the worst PSNR is 57.96 dB (OPENING). That is a guess at how far the IPU's undocumented IDCT could be.
• A test race. The two ffmpeg tests failed at random pictures of OPENING because both wrote the same temporary copy of the file while running in parallel. Each comparison now writes its own copy.
• movies_play in piney-game. From power-on, the three logos take exactly 2 x (146 + 180 + 151) frames of 640 x 448 pictures, all silent. OPENING opens with its sound; its PCM is silent for the first 2.57 s, and it is heard in more than 75 of frames 160-240. START then stops it, and the title goes on.
• The other session tests. They now skip the logos with START as a player would.
• Shots. A GPU shot at frame 100 shows the Bandai logo, and one at frame 2600 a scene of the opening.