Android TTS text longer than 4k chars not playing

问题:

I am using TextToSpeech to play some long texts sometimes, and I have noticed that since Android 4.1.2 if the text is longer than 4000 chars, it does not play.

I do not get any errors, but the text won't be played. Until now I was able to reproduce this just on Android 4.1.2(Samsung Galaxy Nexus, Nexus7).

Is this a bug just in 4.1.2 or is this normal (although I did not find any documentation regarding this behaviour)?

Also I have found a post : onUtteranceCompleted() lost if TTS received is too long which indicates different problems with texts longer than 4000 chars.

EDIT: I tried to split my string in 4k length chunks, and send it to TTS using QUEUE_ADD and I came across another bug: QUEUE_ADD does not work, instead it flushes the existing queue, and only the last chunk gets played.

EDIT2 : this is my call to TTS

mTTS.speak(longText, TextToSpeech.QUEUE_FLUSH, null);

回答1:

MAX_SPEECH_ITEM_CHAR_LENGTH = 4000 in TtsService.java, on 4.1 I see a warn in the code:

    @Override
    public boolean isValid() {
        if (mText == null) {
            Log.wtf(TAG, "Got null text");
            return false;
        }
        if (mText.length() >= MAX_SPEECH_ITEM_CHAR_LENGTH) {
            Log.w(TAG, "Text too long: " + mText.length() + " chars");
            return false;
        }
        return true;
    }

looks like 2.3 splits the text instead, so teorically your code should work on android < 4.1 and not on newer (I don't known when the split was removed), instead you have the opposite :) that is a bit strange

回答2:

No problem on 4.4.2... I split my Strings like this...

//textToSpeech can only cope with Strings with < 4000 characters
int dividerLimit = 3900;
if(textForReading.length() >= dividerLimit) {
    int textLength = textForReading.length();
    ArrayList<String> texts = new ArrayList<String>();
    int count = textLength / dividerLimit + ((textLength % dividerLimit == 0) ? 0 : 1);
    int start = 0;
    int end = textForReading.indexOf(" ", dividerLimit);
    for(int i = 1; i<=count; i++) {
        texts.add(textForReading.substring(start, end));
        start = end;
        if((start + dividerLimit) < textLength) {
            end = textForReading.indexOf(" ", start + dividerLimit);
        } else {
            end = textLength;
        }
    }
    for(int i=0; i<texts.size(); i++) {
        textToSpeech.speak(texts.get(i), TextToSpeech.QUEUE_ADD, null);
    }
} else {
    textToSpeech.speak(textForReading, TextToSpeech.QUEUE_FLUSH, null);
}

回答3:

My solution was to use onUtteranceCompleted(String utteranceId) to know when the first chunk has finished, and then, feed the next chunk to TextToSpeech until they are all finished.

@Override
public void onInit(int status) { //On TTS init
    //guava Splitter
    mChunks=Lists.newLinkedList(Splitter.fixedLength(3999).split(mExtractedText));
    mTTS.setOnUtteranceCompletedListener(this);
    playNextChunk();
}

private void playNextChunk(){
    HashMap<String, String> params = new HashMap<String, String>();
    params.put(TextToSpeech.Engine.KEY_PARAM_UTTERANCE_ID, ""+mChunks.size());
    mTTS.speak(mChunks.poll(), TextToSpeech.QUEUE_FLUSH, params);
}

@Override
public void onUtteranceCompleted(String utteranceId) {
    playNextChunk();
}