[FFmpeg-devel] [PATCH v5 1/2] libavcodec: Added DFPWM1a codec

[Paul B Mahol]

On 3/3/22, Paul B Mahol <onemda at gmail.com> wrote:
> On 2/27/22, Jack Bruienne <jackbruienne at gmail.com> wrote:
>>
>>  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.
>>
>> 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. The
>> accompanying raw format has a channels option to set this. (I expect
>> most users of this will not use multiple channels, but it remains an
>> option just in case.)
>>
>> This patch will be highly useful to ComputerCraft developers who are
>> working with audio, as it is the standard format for audio, and there
>> are few user-friendly encoders out there, and even fewer decoders. It
>> will streamline the process for importing and listening to audio,
>> replacing the need to write code or use tools that require very
>> specific input formats.
>>
>> You may use the CraftOS-PC program (https://www.craftos-pc.cc) to test
>> out DFPWM playback. To use it, run the program and type this command:
>> "attach left speaker" Then run "speaker play <file.dfpwm>" for each file.
>> The app runs in a sandbox, so files have to be transferred in first;
>> the easiest way to do this is to simply drag the file on the window.
>> (Or copy files to the folder at https://www.craftos-pc.cc/docs/saves.)
>>
>> Sample DFPWM files can be generated with an online tool at
>> https://music.madefor.cc. This is the current best way to encode DFPWM
>> files. Simply drag an audio file onto the page, and it will encode it,
>> giving a download link on the page.
>>
>> I've made sure to update all of the docs as per Developer§7, and I've
>> tested it as per section 8. Test files encoded to DFPWM play correctly
>> in ComputerCraft, and other files that work in CC are correctly decoded.
>> I have also verified that corrupt files do not crash the decoder - this
>> should theoretically not be an issue as the result size is constant with
>> respect to the input size.
>>
>> Changes since v4:
>> Fixed missing channel check in decoder.
>>
>> Changes since v3:
>> Added support for multiple interleaved channels, and cleaned up the
>> code a bunch.
>>
>> Changes since v2:
>> I've found that the reference encoder has a few errors, and sounds
>> worse than the Java-based implementation that is used most often. I got
>> in contact with someone who knows DFPWM much better than I do, and I
>> worked with them to make a few adjustments that should improve the
>> audio quality. I also made sure that the output matches the Java
>> codec exactly, so it should have the exact same quality as other codecs.
>>
>> Signed-off-by: Jack Bruienne <jackbruienne at gmail.com>
>> ---
>>   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     | 133 ++++++++++++++++++++++++++++++++++++++
>>   libavcodec/dfpwmenc.c     | 121 ++++++++++++++++++++++++++++++++++
>>   libavcodec/utils.c        |   2 +
>>   libavcodec/version.h      |   2 +-
>>   11 files changed, 272 insertions(+), 1 deletion(-)
>>   create mode 100644 libavcodec/dfpwmdec.c
>>   create mode 100644 libavcodec/dfpwmenc.c
>>
>>
>
>
> Please move channel check to init.
>

Also check for possible overflows when multiplying with 8 the packet->size.