Balrogg: Demonically compacting (up to 15%) lossless Vorbis/Opus recompressor

balrogg losslessly recompresses Ogg Vorbis and Opus files. Archives are typically 8-12% smaller than .ogg files and 3-8% smaller than .opus files.

Releases are not backwards or forwards compatible until v2.0 is reached.

balrogg is licensed under GNU GPL version 3. See COPYING. Report issues to Kamila Szewczyk k@iczelia.net. The project is hosted at https://github.com/iczelia/balrogg.

balrogg e music.ogg music.blr
balrogg d music.blr music.ogg
balrogg -b e *.ogg *.opus
balrogg --progress -9 e music.ogg music.blr

e compresses and d expands. balrogg detects the codec. With -b, every remaining path is processed using the available cores and memory. Encoding appends .blr; decoding removes it. Larger inputs run first.

-p or --progress displays a progress bar on stderr for encoding and decoding, with each Vorbis tuning trial identified separately. Use --progress-lines for logs. Batch progress uses separate lines labeled with the input filename.

Use your package manager or download a binary from GitHub Releases. To build a release tarball, run

./configure
make
sudo make install

The project uses C99 and only the C and math libraries. The Opus parser under src/opus is derived from libopus.

Run ./bootstrap first when building from a Git checkout. It requires autoconf and automake.

-1 through -9 select effort; the default is -9. Through -4, each level adds a residue-model stage and affects decoding. Higher levels only expand the parameter search, so -4 through -9 decode at the same speed. Vorbis tuning evaluates the complete file at each selected setting. The best candidate is retained in the destination file, with at most the best and current candidate present during a trial.

Results for a five-megabyte music file follow.

The encoder refuses files it cannot reproduce exactly, including files with bad checksums, invalid page sequences, unsupported Vorbis features, or no final end-of-stream page.

Vorbis packets with extra padding or alternative floor subclass choices retain normal floor and residue compression. Classword corrections and padding are modeled separately. Shortened packets (packet peeling) use an adaptive byte model.

Opus support is limited to one mono or stereo logical stream with channel mapping family 0. Packets, including OpusHead and OpusTags, are limited to 61,440 bytes; extended frame headers and padding are supported within that limit. Chained and multichannel Opus files are refused. Refusals produce a diagnostic and exit status 1.

Batch mode returns the highest nonzero status reported by any file.

Each file uses one thread and requires seekable input and output files. Vorbis model pages are allocated only when used, without relying on deferred OS allocation.

Supported hosts apply a 2 GiB process memory cap to reject unreasonable allocations. Set BLR_MEMCAP to another size in MiB, or to 0 to disable the cap.

Archives are portable across hosts. Windows builds use MinGW as follows:

./configure --host=x86_64-w64-mingw32 CC=x86_64-w64-mingw32-gcc LDFLAGS=-static
make

A Windows 95 build uses a small KERNEL32 runtime and targets i486.

./configure --host=i686-w64-mingw32 --with-windows-target=win95 \
            CC=i686-w64-mingw32-gcc LDFLAGS=-static
make && make win95-check

win95-check verifies the loader baseline, PE flags, and KERNEL32 imports. An MS-DOS build uses DJGPP and needs an i386 with a DPMI host such as CWSDPMI.

./configure --host=i586-pc-msdosdjgpp CC=i586-pc-msdosdjgpp-gcc
make

DOS batch mode replaces the extension and runs serially. song.ogg becomes song.blr, then expands to song.ogg or song.opu for Opus.