#232 Add DSD Disc ISO support — direct UDF filesystem readerAdd DSD Disc ISO support — direct UDF filesystem reader

[Anonymous]

Hi Maxim,

I've implemented DSD Disc ISO direct reading support for foo_input_sacd,
and I'd like to contribute it to the upstream project.

DSD Disc is a disc image format for publishing DSD audio on recordable
media, standardized by Sony. Unlike SACD ISOs (which use a proprietary
filesystem with SACDMTOC), DSD Disc stores individual DSF files inside
a standard UDF 1.02 volume — the same filesystem used by DVD-Video and
BDMV. Current versions of foo_input_sacd reject these ISOs because
they lack the SACDMTOC signature, even though the audio data is
standard DSD64/128/256.

Implementation approach

Rather than requiring an external UDF library (a heavyweight dependency
for a single purpose), I wrote a lightweight UDF 1.02 parser directly
inside the plugin. Two new files under src/foo_input_sacd/:

udsd_reader_dsd_disc.h (254 lines)
udsd_reader_dsd_disc.cpp (797 lines)

The reader inherits from udsd_reader_t and plugs into the existing
dispatch mechanism in udsd_core.cpp, with essentially zero changes to
the existing SACD/DSF/DFF code paths.

How it works

1. Detection (g_is_dsd_disc): Opens the ISO with filesystem::g_open_read
   (same pattern as g_is_sacd), reads AVDP at LSN 256, walks VDS to find
   LVD/PD, reads FSD, and scans the root directory for a "DSD_DISC"
   subdirectory.

2. UDF file traversal: Starting from the root File Entry, traverse
   directory entries recursively. Each FID with directory flag set and
   name != "DSD_DISC" enters a subdirectory; FIDs with .dsf extension
   become tracks.

3. DSF header parsing: For each found file, read_and validate the
   "DSD " magic, fmt chunk (sample rate, channel count, format_id),
   and data chunk offset. The data offset is used by read_frame()
   for streaming DSD audio direct from the ISO.

4. ID3 tag extraction: If the DSF header's id3_offset field is non-zero,
   parse the ID3v2 tag for TIT2, TPE1, and TALB frames (title, artist,
   album). UTF-16 and UTF-8 with BOM are handled.

5. Playback: read_frame() computes the byte offset within the ISO for
   the current frame and reads via udsd_media_t::read(). seek() works
   by frame index. Multi-channel DSD (up to 6ch) is supported.

Endianness note

UDF stores all multi-byte fields in little-endian, while DSF/ID3 fields
are big-endian (network byte order). The reader keeps the two worlds
separate: UDF struct members are read directly without swap on x86
(where host order matches LE), and DSF fields use ntoh32/ntoh64 macros
(aliases for hton32/hton64, symmetric on all architectures).

Files modified

• src/foo_input_sacd/udsd_reader.h

• Added DSDDISC = 4 to media_type_e enum

• src/foo_input_sacd/udsd_core.cpp

• Added #include "udsd_reader_dsd_disc.h"
• g_is_our_path: checks g_is_dsd_disc() after g_is_sacd() fails
• open(): reassigns media_type to DSDDISC when g_is_dsd_disc() matches
• Reader dispatch: creates udsd_reader_dsd_disc_t for DSDDISC type

Files added

• src/foo_input_sacd/udsd_reader_dsd_disc.h
  254 lines, pure header. Defines:
• dsd_disc_track_t — per-track metadata (offset, channels, rate, ID3)
• UDF structures — udf_tag_t, udf_avdp_t, udf_lvd_t, udf_pd_t,
  udf_fsd_t, udf_fe_t, udf_fid_t, udf_short_ad_t, udf_long_ad_t

• udsd_reader_dsd_disc_t — class declaration (inherits udsd_reader_t)

• src/foo_input_sacd/udsd_reader_dsd_disc.cpp
  797 lines, full implementation:

• g_is_dsd_disc() — static detection probe
• read_sector() / find_avdp() / read_vds() / read_fsd() — UDF walkers
• traverse_directory() — recursive UDF FID enumeration
• read_dsf_header() — DSF chunk parser + data offset calculation
• read_id3_tag() — ID3v2 frame extractor
• Full udsd_reader_t interface: open/close/select_track/read_frame/
  seek/get_info

To apply

The patch is against the current foo_input_sacd snapshot (based on
sacddecoder-0.9.6 from SourceForge, foobar2000 SDK 2023-08-23). The
new code compiles cleanly and follows the existing coding style
(underscore naming, foobar2000 SDK conventions).

I'm happy to adjust anything — formatting, naming, structural
decisions. Let me know if you prefer a different approach (e.g. a
separate file input module, or a factored UDF mini-library shared
between readers).

Best regards

Aaron Leung/aaronleung@vip.qq.com

[Maxim V.Anisiutkin]

Hi Aaron,

It would be great to have some Sony DSD Disc ISO file for testing as well. Could you please point me where to download this?

Sincerely,
Maxim

[Maxim V.Anisiutkin]

Line 693 in patch file:

• offset += 10 + ((frame_size + 1) & ~1);
  offset is undeclared identifier.

[Anonymous]

tks