[Ffmpeg-devel] process an audio stream and find some attributes...

Patrick Fischer patrick_fischer
Mon Jun 27 22:40:58 CEST 2005

I have written an Class to process an mpeg stream(audio/video).
I want to identify the avg loudness of the AudioStream.

By the way I have one class for video and one for audio.
My AudioStream Class has the ability to detect the rigth stream id and 

<http://dict.leo.org/se?lp=ende&p=/Mn4k.&search=ability>But I have two 
-First I don't know how to handel the audio data. (find the avgloudness)

-Second I want to detect changes of the codec.
In some streams the codec can change. (mono->sterio->dts->...)
I think it is not a practical idea to make an av_find_stream_info(...) 
at every Frame. <http://dict.leo.org/se?lp=ende&p=/Mn4k.&search=idea>

attached you find my hole class.
Here are some importend Parts...

I hope you can help me.....


    uint8_t *outbuf;
    outbuf = (uint8_t*)malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE);
    int out_size,len;
    while( !found && av_read_frame(pFormatCtx, &packet)>=0  ) {
        // Is this a packet from the audio stream?
        if(packet.stream_index==audioStream) {
            // Decode Audio frame
            len = avcodec_decode_audio(pCodecCtx, (short *)outbuf, 
                                       packet.data, packet.size);

            if (len < 0) {
                fprintf(stderr, "Error while decoding\n");

            if (out_size > 0) {              
                found = 1;
        // Free the packet that was allocated by av_read_frame

    int avg =0;
    for(int c=0; c<out_size; c++){
        avg += outbuf[c]*outbuf[c] / currentFrameNumber;
    //you can return the data or an avg value
    sAudioFrame frame;
   //    frame.data = outbuf;   
   //    frame.datasize = out_size;
    frame.codec = pCodecCtx->codec_id;
    frame.number = pCodecCtx->frame_number;
    frame.avgloudness = avg;

    if (!found )
        frame.number = -1;

    log->logdevelop("Avgloudness = %d",avg);

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