Implement AC4 support #1838

CastagnaIT · 2025-04-28T16:17:58Z

Description

Implement AC4 audio

TODO: check for possible required changes to AudioCodecHandler

Motivation and context

some months ago i seen some changes on kodi core about ac4
i made an attempt to check if it actually works
unfortunately at today kodi use ffmpeg 7.1.1 and looks like there is no AC4 decoder available
since avcodec_find_decoder_by_name dont return the decoder

I don't know if 7.2 will have it, seem also exists unofficial patched ffmpeg with ac4 support,
but i don't think it's worth it, better wait for the official ffmpeg implementation

How has this been tested?

https://ott.dolby.com/OnDelKits/AC-4/Dolby_AC-4_Online_Delivery_Kit_1.5/help_files/topics/kit_wrapper_HLS_multiplexed_streams.html

Screenshots (if appropriate):

Types of change

Bug fix (non-breaking change which fixes an issue)
Clean up (non-breaking change which removes non-working, unmaintained functionality)
Improvement (non-breaking change which improves existing functionality)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that will cause existing functionality to change)
Cosmetic change (non-breaking change that doesn't touch code)
None of the above (please explain below)

Checklist:

I have read the Contributing document
My code follows the Code Guidelines of this project
My change requires a change to the Wiki documentation
I have updated the documentation accordingly

Copilot

Pull Request Overview

This PR adds support for AC4 audio by extending codec name/fourcc lists, introducing an AC4 parser, updating the ADTS demuxer, and ensuring sessions recognize AC4 streams.

Add NAME_AC4 and FOURCC_AC_4 constants to Utils.h
Introduce CAdaptiveAc4Parser and its FindFrameHeader implementation
Extend ADTSReader to parse AC4 frames and update Session to handle AC4

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

File	Description
src/utils/Utils.h	Added AC4 to codec name and fourcc lists
src/parser/CodecParser.h/.cpp	Added `CAdaptiveAc4Parser` class and header parsing
src/demuxers/ADTSReader.h/.cpp	Added AC4 parsing methods and case handling
src/Session.cpp	Updated stream update logic to recognize AC4

Comments suppressed due to low confidence (1)

src/parser/CodecParser.h:48

No unit tests cover CAdaptiveAc4Parser or AC4 frame parsing; adding tests would help ensure correct behavior and prevent regressions.

class ATTR_DLL_LOCAL CAdaptiveAc4Parser : public AP4_Ac4Parser

Copilot · 2025-05-25T06:53:20Z

src/demuxers/ADTSReader.cpp

+  if (!AP4_SUCCEEDED(stream->Read(buffer.UseData(), AP4_AC3_HEADER_SIZE)))
+    return false;
+
+  CAdaptiveAc3Parser parser;


The AC4 header parser is using CAdaptiveAc3Parser; this should be CAdaptiveAc4Parser to correctly parse AC4 frames.

Suggested change

CAdaptiveAc3Parser parser;

CAdaptiveAc4Parser parser;

Copilot · 2025-05-25T06:53:21Z

src/demuxers/ADTSReader.cpp

+  buffer.SetDataSize(AP4_AC3_HEADER_SIZE);
+
+  if (!AP4_SUCCEEDED(stream->Read(buffer.UseData(), AP4_AC3_HEADER_SIZE)))


Parsing AC4 headers should use AP4_AC4_HEADER_SIZE instead of AP4_AC3_HEADER_SIZE to allocate the correct buffer size.

Suggested change

buffer.SetDataSize(AP4_AC3_HEADER_SIZE);

if (!AP4_SUCCEEDED(stream->Read(buffer.UseData(), AP4_AC3_HEADER_SIZE)))

buffer.SetDataSize(AP4_AC4_HEADER_SIZE);

if (!AP4_SUCCEEDED(stream->Read(buffer.UseData(), AP4_AC4_HEADER_SIZE)))

Copilot · 2025-05-25T06:53:21Z

src/demuxers/ADTSReader.cpp

+  AP4_Size sz = buffer.GetDataSize();
+  parser.Feed(buffer.GetData(), &sz);
+
+  AP4_Ac3Frame frame;


You’re instantiating an AP4_Ac3Frame for AC4 parsing; this should be an AP4_Ac4Frame to match the AC4 parser.

Copilot · 2025-05-25T06:53:22Z

src/parser/CodecParser.cpp

+
+  unsigned char* rawframe = new unsigned char[sync_frame_size];
+
+  // copy the whole frame becasue toc size is unknown


Fix typo: replace “becasue” with “because”.

Suggested change

// copy the whole frame becasue toc size is unknown

// copy the whole frame because toc size is unknown

Copilot · 2025-05-25T06:53:22Z

src/parser/CodecParser.cpp

+  frame.m_Info.m_Ac4Dsi.d.v1.b_uuid = ac4_header.m_BProgramUuidPresent;
+  AP4_CopyMemory(frame.m_Info.m_Ac4Dsi.d.v1.program_uuid, ac4_header.m_ProgramUuid, 16);
+
+  // Calcuate the bit rate mode according to ETSI TS 103 190-2 V1.2.1 Annex B


Fix typo: replace “Calcuate” with “Calculate”.

Suggested change

// Calcuate the bit rate mode according to ETSI TS 103 190-2 V1.2.1 Annex B

// Calculate the bit rate mode according to ETSI TS 103 190-2 V1.2.1 Annex B

Copilot · 2025-05-25T06:53:22Z

src/parser/CodecParser.h

+{
+public:
+  CAdaptiveAc4Parser() {}
+  AP4_Result FindFrameHeader(AP4_Ac4Frame& frame);


[nitpick] Mark this method as override to clarify that it overrides the base class implementation.

Suggested change

AP4_Result FindFrameHeader(AP4_Ac4Frame& frame);

AP4_Result FindFrameHeader(AP4_Ac4Frame& frame) override;

Copilot · 2025-05-25T06:53:22Z

src/parser/CodecParser.cpp

+    return AP4_ERROR_NOT_ENOUGH_DATA;
+  }
+
+  unsigned char* rawframe = new unsigned char[sync_frame_size];


[nitpick] Consider using a std::vector<unsigned char> or smart pointer instead of manual new[]/delete[] to manage frame buffers.

CastagnaIT added On hold PR that is not currently being worked on (e.g. waiting for a 3rd-party release or feedback) Type: Feature non-breaking change which adds functionality labels Apr 28, 2025

wip

8eba386

CastagnaIT force-pushed the ac4 branch from 2107a9d to 8eba386 Compare May 12, 2025 12:07

garbear requested a review from Copilot May 25, 2025 06:51

Copilot AI reviewed May 25, 2025

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Implement AC4 support #1838

Implement AC4 support #1838

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CastagnaIT commented Apr 28, 2025 •

edited

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		buffer.SetDataSize(AP4_AC3_HEADER_SIZE);

		if (!AP4_SUCCEEDED(stream->Read(buffer.UseData(), AP4_AC3_HEADER_SIZE)))


		unsigned char* rawframe = new unsigned char[sync_frame_size];

		// copy the whole frame becasue toc size is unknown

	// copy the whole frame becasue toc size is unknown
	// copy the whole frame because toc size is unknown

	// Calcuate the bit rate mode according to ETSI TS 103 190-2 V1.2.1 Annex B
	// Calculate the bit rate mode according to ETSI TS 103 190-2 V1.2.1 Annex B

	AP4_Result FindFrameHeader(AP4_Ac4Frame& frame);
	AP4_Result FindFrameHeader(AP4_Ac4Frame& frame) override;

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Description

Motivation and context

How has this been tested?

Screenshots (if appropriate):

Types of change

Checklist:

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CastagnaIT commented Apr 28, 2025 •

edited

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