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• How to put audio data in AVFrame for encode

  17 avril 2020, par easy_breezy

  I try to encode raw PCM sound to G711A and G711U and then decode it, with this codecs everything works fine because I can choose any value for AVCodecContext frame_size for encoding, but in case of Opus codec the AVCodecContext frame_size is equal to 120, so if I understood correctly if my input data array size is bigger than 120 then I need to do some kind of buffering and split my input data into several parts and then sequentially put it to AVFrame->data and pass the AVFrame to encoding.

  



  In result I get a very bad sound and I get this result not only when I use Opus codec but also in G711 if I set it's AVCodecContext frame_size to some value that will be less than size of my input data.

  



  So my question is : what it the correct way to encode input data if it's size if bigger than AVCodecContext frame_size ? Do I need to split my input data into some parts that <= AVCodecContext frame_size if so how should I do that ?

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  At this moment my code looks like this :

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  void encode(uint8_t *data, unsigned int length)
{
    int rawOffset = 0;
    int rawDelta = 0;
    int rawSamplesCount = frameEncode->nb_samples <= length ? frameEncode->nb_samples : length;

    while (rawSamplesCount > 0)
    {
        memcpy(frameEncode->data[0], &data[rawOffset], sizeof(uint8_t) * rawSamplesCount);

        encodeFrame();

        rawOffset += rawSamplesCount;
        rawDelta = length - rawOffset;
        rawSamplesCount = rawDelta > frameEncode->nb_samples ? frameEncode->nb_samples : rawDelta;
    }

    av_frame_unref(frameEncode);
}

void encodeFrame()
{
    /* send the frame for encoding */
    int ret = avcodec_send_frame(contextEncoder, frameEncode);
    if (ret < 0)
    {
        LOGE(TAG, "[encodeFrame] avcodec_send_frame error: %s", av_err2str(ret));
        return;
    }

    /* read all the available output packets (in general there may be any number of them) */
    while (ret >= 0)
    {
        ret = avcodec_receive_packet(contextEncoder, packetEncode);
        if (ret < 0 && ret != AVERROR(EAGAIN)) LOGE(TAG, "[encodeFrame] error in avcodec_receive_packet: %s", av_err2str(ret));
        if (ret < 0) break;
        std::pair p = std::pair();
        p.first = (uint8_t *)(malloc(sizeof(uint8_t) * packetEncode->size));
        memcpy(p.first, packetEncode->data, (size_t)packetEncode->size);
        p.second = (unsigned int)(packetEncode->size);

        listEncode.push_back(p); // place encoded data into list to finally create one array of encoded data from it
    }
    av_packet_unref(packetEncode);
}


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  You can see that I split my input data into several parts, then I put it in frame->data and then pass the frame to encoding but I'm not sure that is the correct way.

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  UPD : I noticed that when I use G711 if I set AVCodecContext frame_size to 160 and size of my input data is 160 or 320 everething works fine, but if input data size is 640 then i get bad buzzing sound.

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• Converting PCM-ALAW data to an audio file using ffmpeg

  8 septembre 2020, par bbdd

  In my project, I processed the received RTP packets with the payload, and extracted all the payload to a separate buffer. This payload is - PCM ALAW (Type 8). How do I implement a class that will take as arguments - the file name and a buffer with raw data to create an audio file. Exactly what steps do I have to go through in order to encode raw data into an audio file ? As an example, I used this example.

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• How to modify SPS/PPS aka Codec Private data of a mkv file

  13 novembre 2019, par Minh Nghĩa

  I encode my clip in 5 parts (output is x265 in MKV), using -ss and -t to seek to cut position. Now mkvtoolnix refuses to merge the encoded files, warning that codec private data doesn't match.

  From this question in mkvtoolnix repo, I learned that the codec private data is encoded in PPS/SPS field of the file. I check the encoding settings from mediainfo, and found that all settings are the same, just one file has a different numa-pool argument. I think my files can still be merged.

  How can I edit SPS/PPS data to fool mkvmerge into merging my files ? Thanks !