FormatConverterStream causing dropouts (under-runs?) during channel conversion #2135

z-l-p · 2025-08-19T14:17:14Z

z-l-p
Aug 19, 2025

I'm using FormatConverterStream to convert URLstreams with different sampling rates and channel counts, so they can eventually be sent to a mixer for further processing. I've observed the following:

Sampling Rate conversion works great
Channel conversion (mono to stereo) works fine for a few seconds before the sound breaks up.

I see no changes in the log when the sound starts breaking up, but the pace of the messages slows down to match the gaps in the audio:

[I] StreamCopy.h : 173 - StreamCopy::copy  1024 -> 1024 -> 1024 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  376 -> 376 -> 376 bytes - in 1 hops

(also, if I specify a larger buffer size in the StreamCopy constructor, I see no effect in the copy sizes decribed in the logs, but maybe I'm misunderstanding that?)

Test sketch that shows the problem with a mono -> stereo conversion after a few seconds:


#include "AudioTools.h"
#include "AudioTools/AudioCodecs/CodecMP3Helix.h"

const char *ssid = "";          // Change this to your WiFi SSID
const char *password = "";  // Change this to your WiFi password

AudioInfo out_info(44100, 2, 16); // destination format for I2S (all streams will be converted to this)
URLStream url;
I2SStream i2s;
VolumeStream vol(i2s);
FormatConverterStream conv(vol);
MultiDecoder multi(url);
MP3DecoderHelix mp3;
EncodedAudioStream dec(&conv, &multi); // Decoding stream
StreamCopy copier(dec, url); // copy url to decoder

void setup(){
  Serial.begin(115200);
  Serial.println();
  Serial.println("******************************************************");
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info);  
  
  // setup i2s
  auto config = i2s.defaultConfig(TX_MODE);
  config.copyFrom(out_info);
  // Custom I2S pins for my Xaio board
  config.pin_ws = 9; // (DAC "LRCK")
  config.pin_bck = 7; // (DAC "BCK")
  config.pin_data = 8; // (DAC "DIN")
  i2s.begin(config);

// setup VolumeStream
  auto vcfg = vol.defaultConfig();
  vcfg.allow_boost = true; // activate amplification using linear control
  vol.begin(vcfg);

  // setup audio converter
  conv.begin(multi.audioInfo(), out_info);

  // setup decoder
  multi.addDecoder(mp3, "audio/mpeg");
  dec.begin();
  url.begin("https://locus.creacast.com:9443/kernot_lillypilly.mp3");  // MONO STREAM
}

void loop() {
  copier.copy();
}

pschatzmann · 2025-08-19T14:52:19Z

pschatzmann
Aug 19, 2025
Maintainer

Please share the log: double check that i2s gets informormed about the 2 channels.
Did you try just using the ChannelFormatConverterStream instead ?

2 replies

z-l-p Aug 20, 2025
Author

I haven't tried ChannelFormatConverterStream yet (because I also need samplerate conversion for some streams) but here's the full log. (It seems like I2S begins in stereo, switches to mono but then back to stereo (with 1->2 channel conversion). The odd thing is that the conversion works great for a few seconds before the sound falls apart. (I've tried several streams with different sample rates and channel counts. The problem only occurs on mono streams.)

[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 -  sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SConfigESP32V1.h : 78 - rx/tx mode: TX_MODE
[I] I2SConfigESP32V1.h : 79 - port_no: 0
[I] I2SConfigESP32V1.h : 80 - is_master: Master
[I] I2SConfigESP32V1.h : 81 - sample rate: 44100
[I] I2SConfigESP32V1.h : 82 - bits per sample: 16
[I] I2SConfigESP32V1.h : 83 - number of channels: 2
[I] I2SConfigESP32V1.h : 84 - signal_type: Digital
[I] I2SConfigESP32V1.h : 85 - buffer_count:6
[I] I2SConfigESP32V1.h : 86 - buffer_size:512
[I] I2SConfigESP32V1.h : 87 - auto_clear: true
[I] I2SConfigESP32V1.h : 89 - i2s_format: I2S_STD_FORMAT
[I] I2SConfigESP32V1.h : 101 - pin_bck: 7
[I] I2SConfigESP32V1.h : 104 - pin_ws: 9
[I] I2SConfigESP32V1.h : 107 - pin_data: 8
[I] I2SESP32V1.h : 259 - dma_frame_num: 768
[I] I2SESP32V1.h : 164 - tx: 8, rx: -1
[I] I2SESP32V1.h : 283 - mclk_multiple=256
[I] VolumeStream.h : 199 - setVolume: 1.000000 at 0
[I] VolumeStream.h : 199 - setVolume: 1.000000 at 1
[I] ResampleStream.h : 129 - -> ResampleStream:
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioStreamsConverter.h : 465 - -> NumberFormatConverterStream:
[I] AudioStreamsConverter.h : 134 - --> ChannelFormatConverterStream
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioStreamsConverter.h : 177 - --> ChannelFormatConverterStream
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioStreamsConverter.h : 465 - -> NumberFormatConverterStream:
[I] AudioStreamsConverter.h : 179 - begin 2 -> 2 channels
[I] AudioStreamsConverter.h : 24 - begin 2 -> 2 channels
[I] AudioStreamsConverter.h : 502 - begin 16 -> 16 bits
[I] AudioStreamsConverter.h : 515 - no bit conversion: 16 -> 16
[I] ResampleStream.h : 64 - begin step_size: 1.000000
[I] ResampleStream.h : 145 - setStepSize: 1.000000
[I] ResampleStream.h : 145 - setStepSize: 1.000000
[I] ResampleStream.h : 129 - -> ResampleStream:
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] URLStream.h : 90 - virtual bool audio_tools::URLStream::begin(const char*, const char*, MethodID, const char*, const char*): https://locus.creacast.com:9443/kernot_lillypilly.mp3
[I] Url.h : 59 - Url::parse
[I] Url.h : 97 - url->https://locus.creacast.com:9443/kernot_lillypilly.mp3
[I] Url.h : 98 - host->locus.creacast.com
[I] Url.h : 99 - protocol->https
[I] Url.h : 100 - path->/kernot_lillypilly.mp3
[I] Url.h : 101 - port->9443
[I] URLStream.h : 378 - WiFiClientSecure
[I] HttpRequest.h : 240 - process connecting to host locus.creacast.com port 9443
[I] HttpRequest.h : 367 - is connected true  with timeout 60000
[I] HttpRequest.h : 251 - Free heap: 205412
[I] HttpHeader.h : 262 - HttpHeader::write
[I] HttpHeader.h : 417 - -> GET /kernot_lillypilly.mp3 HTTP/1.1
[I] HttpHeader.h : 196 -  -> Host: locus.creacast.com 
[I] HttpHeader.h : 196 -  -> Connection: keep-alive 
[I] HttpHeader.h : 196 -  -> Accept-Encoding: identity 
[I] HttpHeader.h : 196 -  -> Accept: */* 
[I] HttpHeader.h : 338 -  -> <CR LF> 
[I] HttpRequest.h : 316 - Request written ... waiting for reply
[I] HttpHeader.h : 230 - Waiting for data...
[I] HttpHeader.h : 239 - Data available: 481
[I] HttpHeader.h : 110 - Content-Type: audio/mpeg
[I] HttpRequest.h : 181 - no CONTENT_LENGTH found in reply
[I] URLStream.h : 98 - contentLength: 0
[I] URLStream.h : 241 - Request written ... waiting for reply
[I] URLStream.h : 105 - ==> http status: 200
[I] URLStream.h : 105 - ==> http status: 200
[I] MultiDecoder.h : 247 - mime from http request: audio/mpeg
[I] MultiDecoder.h : 199 - Using decoder for audio/mpeg (audio/mpeg)
[I] CodecMP3Helix.h : 82 - virtual bool audio_tools::MP3DecoderHelix::begin()
[I] MultiDecoder.h : 208 - Decoder audio/mpeg started
[I] StreamCopy.h : 173 - StreamCopy::copy  1024 -> 1024 -> 1024 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  376 -> 376 -> 376 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  1024 -> 1024 -> 1024 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  376 -> 376 -> 376 bytes - in 1 hops
[I] AudioTypes.h : 124 - MP3DecoderHelix sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] ResampleStream.h : 145 - setStepSize: 1.000000
[I] ResampleStream.h : 129 - -> ResampleStream:
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] I2SStream.h : 105 - restarting i2s
[I] AudioTypes.h : 124 - I2SStream sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 -  sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] I2SConfigESP32V1.h : 78 - rx/tx mode: TX_MODE
[I] I2SConfigESP32V1.h : 79 - port_no: 0
[I] I2SConfigESP32V1.h : 80 - is_master: Master
[I] I2SConfigESP32V1.h : 81 - sample rate: 44100
[I] I2SConfigESP32V1.h : 82 - bits per sample: 16
[I] I2SConfigESP32V1.h : 83 - number of channels: 1
[I] I2SConfigESP32V1.h : 84 - signal_type: Digital
[I] I2SConfigESP32V1.h : 85 - buffer_count:6
[I] I2SConfigESP32V1.h : 86 - buffer_size:512
[I] I2SConfigESP32V1.h : 87 - auto_clear: true
[I] I2SConfigESP32V1.h : 89 - i2s_format: I2S_STD_FORMAT
[I] I2SConfigESP32V1.h : 101 - pin_bck: 7
[I] I2SConfigESP32V1.h : 104 - pin_ws: 9
[I] I2SConfigESP32V1.h : 107 - pin_data: 8
[I] I2SESP32V1.h : 259 - dma_frame_num: 1536
[I] I2SESP32V1.h : 164 - tx: 8, rx: -1
[I] I2SESP32V1.h : 283 - mclk_multiple=256
[W] I2SESP32V1.h : 241 - Using channel_format: I2SChannelSelect::Left for mono
[I] AudioStreamsConverter.h : 465 - -> NumberFormatConverterStream:
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] ResampleStream.h : 145 - setStepSize: 1.000000
[I] ResampleStream.h : 129 - -> ResampleStream:
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioStreamsConverter.h : 134 - --> ChannelFormatConverterStream
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioStreamsConverter.h : 465 - -> NumberFormatConverterStream:
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] ResampleStream.h : 145 - setStepSize: 1.000000
[I] ResampleStream.h : 129 - -> ResampleStream:
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 105 - restarting i2s
[I] AudioTypes.h : 124 - I2SStream sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 -  sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SConfigESP32V1.h : 78 - rx/tx mode: TX_MODE
[I] I2SConfigESP32V1.h : 79 - port_no: 0
[I] I2SConfigESP32V1.h : 80 - is_master: Master
[I] I2SConfigESP32V1.h : 81 - sample rate: 44100
[I] I2SConfigESP32V1.h : 82 - bits per sample: 16
[I] I2SConfigESP32V1.h : 83 - number of channels: 2
[I] I2SConfigESP32V1.h : 84 - signal_type: Digital
[I] I2SConfigESP32V1.h : 85 - buffer_count:6
[I] I2SConfigESP32V1.h : 86 - buffer_size:512
[I] I2SConfigESP32V1.h : 87 - auto_clear: true
[I] I2SConfigESP32V1.h : 89 - i2s_format: I2S_STD_FORMAT
[I] I2SConfigESP32V1.h : 101 - pin_bck: 7
[I] I2SConfigESP32V1.h : 104 - pin_ws: 9
[I] I2SConfigESP32V1.h : 107 - pin_data: 8
[I] I2SESP32V1.h : 259 - dma_frame_num: 768
[I] I2SESP32V1.h : 164 - tx: 8, rx: -1
[I] I2SESP32V1.h : 283 - mclk_multiple=256
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] AudioTypes.h : 124 - in: sample_rate: 44100 / channels: 1 / bits_per_sample: 16
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] I2SStream.h : 96 - virtual void audio_tools::I2SStream::setAudioInfo(audio_tools::AudioInfo)
[I] AudioTypes.h : 124 - out: sample_rate: 44100 / channels: 2 / bits_per_sample: 16
[I] StreamCopy.h : 173 - StreamCopy::copy  1024 -> 1024 -> 1024 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  376 -> 376 -> 376 bytes - in 1 hops
[I] StreamCopy.h : 173 - StreamCopy::copy  1024 -> 1024 -> 1024 bytes - in 1 hops

z-l-p Aug 20, 2025
Author

A hint:
The mono streams are playing at double the sampling rate. It's been hard to tell on my test streams of environmental audio, but here's an old radio show that makes it obvious:
https://archive.org/download/OTRR_This_Is_Your_FBI_Singles/This%20Is%20Your%20FBI%2051-12-28%20(352)%20The%20Intruder.mp3

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FormatConverterStream causing dropouts (under-runs?) during channel conversion #2135

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z-l-p Aug 19, 2025

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pschatzmann Aug 19, 2025 Maintainer

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z-l-p
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pschatzmann
Aug 19, 2025
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