How to decode AAC using avcodec_decode_audio4?

问题:

I changed in my code avcodec_decode_audio3 to avcodec_decode_audio4 and added the frame handling. But now I cannot decode AAC frames anymore.

Why does avcodec_decode_audio4 return -22 (invalid argument)? Following the answer below, does this have something to do with the parameters in AVContext that need to be set?

I had to use avcodec_decode_audio4 because I updated my ffmpeg and then got the following error:

[NULL @ 0xb14f020] Custom get_buffer() for use withavcodec_decode_audio3() detected. 
         Overriding with avcodec_default_get_buffer
[NULL @ 0xb14f020] Please port your application to avcodec_decode_audio4()

According to Buffer error in avcodec_decode_audio4() this is a regression, is there any other solution for this than going back to ffmpeg < 0.8 ?

The decoder using avcodec_decode_audio4:

AVCodec *codec;
AVCodecContext *avCtx;
AVFrame * decoded_frame = NULL;
uint8_t *outbuf = static_cast<uint8_t *>(malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE));
AVPacket avPacket;

main(){
    av_register_all();
    codec = avcodec_find_decoder(CODEC_ID_AAC);

    //set parameters
    avCtx = avcodec_alloc_context3(codec);
    avCtx->channels = 1;
    avCtx->sample_rate = 44100;
    avCtx->bit_rate=16;

    if (avcodec_open2(avCtx, codec, NULL) < 0) printf("Could not open codec\n");

    av_init_packet(&avPacket);

    //Main decoder loop
    while(1) 
        my_frame_decoder();
    return 0;
}

void my_frame_decoder() {
    //get data
    ...
    avPacket.size = numBytes;
    avPacket.data = inputBytes;
    int len;

    while (avPacket.size > 0) {

    int got_frame = 0;
    if (!decoded_frame) {
        if (!(decoded_frame = avcodec_alloc_frame())) {
            printf("out of memory");
            return;
        }
    } else {
        avcodec_get_frame_defaults(decoded_frame);
    }

    //-------------------->> returns always -22
    len = avcodec_decode_audio4(avCtx, decoded_frame, &got_frame, &avPacket); 

    //do something with the decoded frame
    ...
    avPacket.size -= len;
    avPacket.data += len;
    }

    return;
}

回答1:

After hours of searching, i found out that the dec_ctx of the avcodec_decode_audio4 must be opened by a dec_codec initialised by av_find_best_stream()

1° av_find_best_stream(in_fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1,
                &dec_codec, 0);<br>
2° dec_ctx = m_in_aud_strm->codec;<br>
3° av_opt_set_int(dec_ctx, "refcounted_frames", 1, 0);<br>
4° avcodec_open2(dec_ctx, dec_codec, NULL)<br>
.
.
.
5° avcodec_decode_audio4(dec_ctx, pFrame, &got_frame, &pkt);

回答2:

I think the problem is the parameters set in your codec's context. Please refer to https://www.ffmpeg.org/doxygen/trunk/structAVCodecContext.html for setting the parameters, which has changed from avcodec_decode_audio3 to avcodec_decode_audio4.

回答3:

No solution but a workaround is to go back to older builds. After testing various builds that work with avcodec_decode_audio3, I thought it might be useful for others to know that ffmpeg-0.10.14.tar.bz2 from https://ffmpeg.org/releases/ works.