Opus 1.4 Corrupted audio while encode of 128 channels

[NickolayGerasimenko]

Environment

Opus 1.4 (commit: 82ac57d)
OS: Win/MacOS

Repro steps

I have very simple encoder as below,
I try to encode 128 channels where I have sine wave on every channel,
I set total bitrate as 64kbps * 128 = 8192kbps

So I instantiate Encoder as follows:

Encoder encoder(8192, 48000, 128);

Actual result:

Audio corrupted on last channels, up to total loss of audio in last channel.

Issue can be reproduced on any number of channels depending on set total bitrate.

Expected result:

Audio should be of good quality in every channel if set total bitrate as 64kbps * channels

Results on different bitrates:

total bitrate 8192kbps - no audio on 128th channel at all:

total bitrate 16384kbps - it's 128kbps per channel, still 128th channel is corrupted:

Workaround:

Only after setting total bitrate to 20480kbps audio looks fine.

Encoder::Encoder(int bitrateKbps, int sampleRate, int numChannels)
{
    int error = 0;
    msEncoder_ = opus_multistream_encoder_create(sampleRate, numChannels, numChannels, 0, kChannelMapping.data(), OPUS_APPLICATION_AUDIO, &error);

    if (error != OPUS_OK)
        throw std::logic_error(std::string("Failed to create opus mulistream encoder, error: ") + opus_strerror(error));

    opus_multistream_encoder_ctl(msEncoder_, OPUS_SET_BITRATE(bitrateKbps * 1000));
    opus_multistream_encoder_ctl(msEncoder_, OPUS_SET_VBR(0));
    opus_multistream_encoder_ctl(msEncoder_, OPUS_SET_PACKET_LOSS_PERC(5));
    opus_multistream_encoder_ctl(msEncoder_, OPUS_SET_COMPLEXITY(5));
    opus_multistream_encoder_ctl(msEncoder_, OPUS_SET_BANDWIDTH(OPUS_AUTO));
}

Encoder::~Encoder()
{
    opus_multistream_encoder_destroy(msEncoder_);
}

bool Encoder::encode(const float* inBuf, int numInputSamples, unsigned char *outBuf, int outBufCapacity, int& encBytes)
{
    encBytes = opus_multistream_encode_float(msEncoder_, inBuf, numInputSamples, outBuf, outBufCapacity);

    if (encBytes < 0)
    {
        return false;
    }

    return true;
}