How to properly start/stop/restart URLStreams?

[bjoerngiesler]

What's the correct way of stopping playback and starting again on URL streams?

The below code walks through a list of URLs, setting up an URLStream -> EncodedAudioStream -> VolumeMeter pipeline, which is copied to an I2SStream with a StreamCopy operation. (The VolumeMeter is purely for visualization purposes with the internal LED, I don't have a speaker here right now...)

The first URL plays fine. Starting the second URL fails in urlStream.begin(). If I do an urlStream.end() before, the output is

Stopping.
[I] URLStreamESP32.h : 414 - HTTP_EVENT_DISCONNECTED
[I] AudioEncoded.h : 185 - virtual void audio_tools::EncodedAudioOutput::end()
[I] CodecMP3Helix.h : 93 - virtual void audio_tools::MP3DecoderHelix::end()
[E] URLStreamESP32.h : 304 - esp_http_client_write: -1
libhelix - Could not write result to out: 0 of 4608 written
Starting stream 'http://s1-webradio.rockantenne.de/rockantenne/stream/mp3'
[I] URLStreamESP32.h : 206 - wifi country: 01 
E (13892) HTTP_CLIENT: No transport found
[I] URLStreamESP32.h : 392 - HTTP_EVENT_ERROR
[E] URLStreamESP32.h : 263 - esp_http_client_open
Opening 'http://s1-webradio.rockantenne.de/rockantenne/stream/mp3' failed

If I don't do the urlStream.end(), the output is

Stopping.
[I] AudioEncoded.h : 185 - virtual void audio_tools::EncodedAudioOutput::end()
[I] CodecMP3Helix.h : 93 - virtual void audio_tools::MP3DecoderHelix::end()
Starting stream 'http://s1-webradio.rockantenne.de/rockantenne/stream/mp3'
[I] URLStreamESP32.h : 206 - wifi country: 01 

... and there it hangs in an infinite loop.

I have confirmed that both streams work by switching their order. Here's the code:

#include <Arduino.h>
#include <AudioTools.h>
#include <AudioTools/AudioCodecs/CodecMP3Helix.h>
#include <AudioTools/Communication/HTTP/URLStreamESP32.h>
#include <WiFiMulti.h>

#include <string>

static const std::string ssid = "xxx"; // removed for anonymization purposes
static const std::string wpakey = "xxx";

std::vector<std::string> urlList = {
    "http://s1-webradio.antenne.de/antenne",
    "http://s1-webradio.rockantenne.de/rockantenne/stream/mp3",
};
static unsigned int urlIndex = 0;

static const uint8_t P_I2S_DATA_OUT = 2;
static const uint8_t P_I2S_WS       = 3;
static const uint8_t P_I2S_BCK      = 4;

static unsigned long playMS = 5000;
static unsigned long playNext;

WiFiMulti wifiMulti;
I2SStream i2s;
MP3DecoderHelix mp3;
URLStreamESP32 urlStream;
EncodedAudioStream encStream(&mp3);
VolumeMeter volume(encStream);
StreamCopy copier(i2s, volume);

void setup(void) {
    Serial.begin(115200);
    while(!Serial) delay(100);
    delay(3000);

    Serial.println("Connecting to Wifi.");
    wifiMulti.addAP(ssid.c_str(), wpakey.c_str());
    wifiMulti.run();
    while (WiFi.status() != WL_CONNECTED) delay(1500);
    Serial.println("Connected.");

    pinMode(LED_BUILTIN, OUTPUT);

    AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info);

    auto cfg = i2s.defaultConfig(TX_MODE);
    cfg.pin_data = P_I2S_DATA_OUT;
    cfg.pin_ws = P_I2S_WS;
    cfg.pin_bck = P_I2S_BCK;
    cfg.is_master = true;
    i2s.begin(cfg);
    
    encStream.setStream(urlStream);

    playNext = millis() + playMS;

    encStream.addNotifyAudioChange(volume);
    encStream.addNotifyAudioChange(i2s);

    Serial.printf("Starting stream '%s'\n", urlList[urlIndex].c_str());
    urlStream.begin(urlList[urlIndex].c_str(), "audio/mp3");
    volume.begin(urlStream.audioInfo());
    mp3.begin();
    encStream.begin(); // start playing
}

void loop(void) {
    copier.copy();
    analogWrite(LED_BUILTIN, (volume.volume()/32767)*255);

    if(millis() > playNext) {
        Serial.printf("Stopping.\n");
        // Commenting in the next line causes a HTTP_EVENT_ERROR on urlStream.begin() a few lines down.
        // Commenting it out causes a hang in the same location.
        urlStream.end(); 
        encStream.end();

        urlIndex = (urlIndex+1)%urlList.size();
        
        Serial.printf("Starting stream '%s'\n", urlList[urlIndex].c_str());
        if(urlStream.begin(urlList[urlIndex].c_str(), "audio/mp3") == false) {
            Serial.printf("Opening '%s' failed\n", urlList[urlIndex].c_str());
            while(true) delay(1);
        }
        encStream.begin(); // start playing

        playNext = millis() + playMS;
    }

    vTaskDelay(1);
}

[pschatzmann]

I recommend to avoid to build the audio processing chain on the input side if ever possilbe. A better way to handle this is
URLStream -copy-> EncodedAudioStream -> VolumeMeter -> I2SStream

This is

• more efficient
• better tested

Can you review the URLStreamESP32. I think the issue is that end is not setting client_handle to nullpointer.

[pschatzmann]

So that would be using the OutputMixer intead...

[bjoerngiesler]

Yes, but that only outputs to a Print and not a Stream, so a Master Volume after the mixer doesn't work. But that's not even the problem; I had crashes / log complaints about inactive nodes whenever I had multiple StreamCopys in a pipeline. With the pull setup, it works...

[pschatzmann]

A Stream is a sublass of Print, so Stream is automatically supported as well...

[bjoerngiesler]

Hm. Yes you're right. TBH I don't know or remember (except that I was quite desperate with either crashes or "Inactive" log entries despite having called begin() on everything), and will have to build an example to try. I will do that.

[bjoerngiesler]

@pschatzmann Your change solved the issue, wonderful!!! No hangs and no error messages on either of the variants. There is a slight pop / click when the new stream starts, I've inserted a encStream.flush(); urlStream.flush(); but that doesn't fix it, so I'm sure the MP3 decoder keeps some buffer. Attaching a crappy phone recording. No big deal though.
Pops while changing streams.mp3