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ConvAgent: fix agent voice truncation on remote clients (Opus)

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Long ElevenLabs audio messages were cut off on remote clients:
- the client Opus decode buffer was only 32000 bytes (~0.88s), so the
  engine decoder aborted with "Decompression buffer too small" and
  dropped the tail of any packet longer than that;
- the server also encoded a whole message as a single Opus packet, which
  the engine encoder caps at 76 frames (~1.52s), silently dropping the rest.
The host/authority plays raw PCM and never decodes, so standalone and
listen-server hosts were unaffected, which masked the bug.

Fix (HandleAudioReceived + MulticastReceiveAgentAudio_Implementation):
- sub-chunk the Opus encode into <=40-frame (25600-byte, 0.8s) blocks,
  one RPC each: stays under both the 76-frame encode cap and the client
  decode buffer, and keeps each Unreliable RPC small;
- raise the client decode buffer 32000 -> 64*1024 as headroom.

Empirically confirmed: networked client logged 16x "Decompression buffer
too small" with Opus active; standalone (Opus equally active) logged zero.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
j.foucher
2026-07-01 14:11:28 +02:00
parent 4854a7fa9a
commit 2ca5643f32
1 changed files with 43 additions and 16 deletions
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41
Unreal/PS_AI_Agent/Plugins/PS_AI_ConvAgent/Source/PS_AI_ConvAgent/Private/PS_AI_ConvAgent_ElevenLabsComponent.cpp
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@@ -1231,9 +1231,30 @@ void UPS_AI_ConvAgent_ElevenLabsComponent::HandleAudioReceived(const TArray<uint
if (OpusEncoder.IsValid())
{
// Opus path: compress then send.
// Opus path: compress then send, in sub-blocks.
//
// A whole ElevenLabs message can be several seconds. Two hard limits
// force us to split it before each Encode()/RPC:
// 1. UE's Opus encoder caps ONE packet at 76 frames (~1.52s) — frames
// beyond that are silently dropped at encode (VoiceCodecOpus.cpp).
// 2. The client decode buffer only holds ~44 frames (~0.88s) before
// the engine decoder aborts with "Decompression buffer too small"
// and drops the packet tail (MulticastReceiveAgentAudio_Implementation).
// 40 frames (25600 bytes, 0.8s) stays safely under BOTH, so nothing is
// truncated on server or client. It also keeps each Unreliable RPC small.
static constexpr int32 BytesPerFrame =
(PS_AI_ConvAgent_Audio_ElevenLabs::SampleRate / 50)
* PS_AI_ConvAgent_Audio_ElevenLabs::Channels
* static_cast<int32>(sizeof(int16)); // 640 at 16kHz mono
static constexpr int32 MaxOpusChunkBytes = 40 * BytesPerFrame; // 25600 = 0.8s
int32 Offset = 0;
while (Offset < PCMData.Num())
{
const int32 BlockBytes = FMath::Min(MaxOpusChunkBytes, PCMData.Num() - Offset);
uint32 CompressedSize = static_cast<uint32>(OpusWorkBuffer.Num());
OpusEncoder->Encode(PCMData.GetData(), PCMData.Num(),
OpusEncoder->Encode(PCMData.GetData() + Offset, BlockBytes,
OpusWorkBuffer.GetData(), CompressedSize);
if (CompressedSize > 0)
@@ -1243,16 +1264,17 @@ void UPS_AI_ConvAgent_ElevenLabsComponent::HandleAudioReceived(const TArray<uint
if (bNetAudioDebug)
{
const float Ratio = (CompressedSize > 0)
? static_cast<float>(PCMData.Num()) / static_cast<float>(CompressedSize)
: 0.0f;
const float Ratio = static_cast<float>(BlockBytes) / static_cast<float>(CompressedSize);
UE_LOG(LogPS_AI_ConvAgent_ElevenLabs, Log,
TEXT("[NET-SRV] Opus audio chunk: %u bytes sent (raw %d → %.1fx compression)."),
CompressedSize, PCMData.Num(), Ratio);
CompressedSize, BlockBytes, Ratio);
}
MulticastReceiveAgentAudio(CompressedData);
}
Offset += BlockBytes;
}
}
else
{
@@ -2533,7 +2555,12 @@ void UPS_AI_ConvAgent_ElevenLabsComponent::MulticastReceiveAgentAudio_Implementa
if (OpusDecoder.IsValid())
{
// Opus path: decode compressed audio.
const uint32 MaxDecompressedSize = 16000 * 2;
// Buffer must hold a full packet's decoded PCM. The engine decoder aborts
// with "Decompression buffer too small to decode voice" (dropping the
// packet tail) if this is smaller than the packet needs. The server caps
// packets at 40 frames (25600 bytes); 64KB gives ample headroom even up to
// the engine's 76-frame (~48640 bytes) maximum, so no packet is truncated.
const uint32 MaxDecompressedSize = 64 * 1024;
PCMBuffer.SetNumUninitialized(MaxDecompressedSize);
uint32 DecompressedSize = MaxDecompressedSize;
OpusDecoder->Decode(AudioData.GetData(), AudioData.Num(),