On 3/7/22 06:03, Tomas Härdin wrote:
tor 2022-03-03 klockan 10:44 -0500 skrev Jack Bruienne:
From the wiki page (https://wiki.vexatos.com/dfpwm):
DFPWM (Dynamic Filter Pulse Width Modulation) is an audio codec
created by Ben “GreaseMonkey” Russell in 2012, originally to be
used
as a voice codec for asiekierka's pixmess, a C remake of 64pixels.
It is a 1-bit-per-sample codec which uses a dynamic-strength one-
pole
low-pass filter as a predictor. Due to the fact that a raw DPFWM
decoding
creates a high-pitched whine, it is often followed by some post-
processing
filters to make the stream more listenable.
This sounds similar to something I wrote for the Atari 2600 a number of
years ago (https://www.pouet.net/prod.php?which=59283 )
I found an encoder online for DFPWM, and it seems to suffer from the
same "beeping" that my debeeping hack fixes (suppressing 0xAA and 0x55
bytes). Perhaps a similar hack could be useful in dfpwmenc.c
I'm curious how this works. Do you just cut out those bytes from the encoder
output, or is it modified in some way? Wouldn't removing the data entirely
eventually cause much of the audio to be lost?
It has recently gained popularity through the ComputerCraft mod for
Minecraft, which added support for audio through this codec, as well
as
the Computronics expansion which preceeded the official support.
These
both implement the slightly adjusted 1a version of the codec, which
is
the version I have chosen for this patch.
This patch adds a new codec (with encoding and decoding) for DFPWM1a.
The codec sources are pretty simple: they use the reference codec
with
a basic wrapper to connect it to the FFmpeg AVCodec system.
To clarify, the codec does not have a specific sample rate - it is
provided by the container (or user), which is typically 48000, but
has
also been known to be 32768. The codec does not specify channel info
either, and it's pretty much always used with one mono channel.
However, since it appears that libavcodec expects both sample rate
and
channel count to be handled by either the codec or container, I have
made the decision to allow multiple channels interleaved, which as
far
as I know has never been used, but it works fine here nevertheless.
From experience it's usually better to be strict when it comes to stuff
like this. The ComputerCraft people should work out a standard for
this, preferably a container. We've had a similar problem in FreeDV
where which codec was being used was implicit most of the time, which
has been resolved with the .c2 format.
I think the best standardized container for DFPWM will be WAV. I'll have to
figure out the best place to properly standardize this, but one first step may
be to implement this in CC directly. Unfortunately, ComputerCraft is currently
without a maintainer - the previous one stepped down in December, and no
changes are being made outside of critical bugfixes. I do hope to pick up
development in the future, and I already run a reimplementation of the mod
outside Minecraft, but as it stands today, getting this to be picked up by
users will be quite difficult.
However, I do also maintain my own audio processing library AUKit, which now
includes support for DFPWM in WAV. Since CC only has a basic raw DFPWM player
built-in (which strictly requires 48kHz mono audio), many users turn to it to
play more complex formats like WAV with a different sample rate, FLAC, etc.
This may be a decent start, but it's far from having full support built-in.
I'll see if I can get in contact with the owner of the DFPWM wiki page. This
will be especially important if this patch gets merged, as people likely won't
see that you can use FFmpeg on those pages. I am able to submit pull requests
to the ComputerCraft documentation site, however, so I'm able to get changes
made there much easier.
In the meantime, I've made a sort-of RFC for the
format:https://gist.github.com/MCJack123/90c24b64c8e626c7f130b57e9800962c
---
Changelog | 1 +
MAINTAINERS | 1 +
doc/general_contents.texi | 1 +
libavcodec/Makefile | 2 +
libavcodec/allcodecs.c | 2 +
libavcodec/codec_desc.c | 7 ++
libavcodec/codec_id.h | 1 +
libavcodec/dfpwmdec.c | 134
++++++++++++++++++++++++++++++++++++++
libavcodec/dfpwmenc.c | 121 ++++++++++++++++++++++++++++++++++
libavcodec/utils.c | 2 +
libavcodec/version.h | 4 +-
11 files changed, 274 insertions(+), 2 deletions(-)
create mode 100644 libavcodec/dfpwmdec.c
create mode 100644 libavcodec/dfpwmenc.c
Patch doesn't apply on current master (e645a1d)
I'll update the patch to apply to the current master, but I feel like by the
time this next gets reviewed master may break again. Should I just keep
updating the patch to master and resubmitting whenever I notice a new commit
breaks it?
/Tomas
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