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• How does ffmpeg extract audio data from mp3 files ?

  13 août 2022, par aszswaz

  In the ffmpeg documentation, an example of mp2 decoding is given. I try to apply this to mp3 :

  


  #define SOURCE_FILE "ignore/audio01.mp3"
#define TARGET_FILE "ignore/target-audio01.pcm"
#define AUDIO_INBUF_SIZE 20480
#define AUDIO_REFILL_THRESH 4096
#define av_perr(errnum) \
    char av_err_buff[AV_ERROR_MAX_STRING_SIZE]; \
    av_strerror(errnum, (char *) &av_err_buff, AV_ERROR_MAX_STRING_SIZE); \
    fprintf(stderr, "\033[91m%s\033[0m\n", av_err_buff);

static int decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame, FILE *outfile) {
    int ret, i, j;
    int data_size;

    ret = avcodec_send_packet(dec_ctx, pkt);
    if (ret < 0) {
        av_perr(ret);
        return EXIT_FAILURE;
    }

    while (ret >= 0) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            break;
        } else if (ret < 0) {
            av_perr(ret);
            return EXIT_FAILURE;
        }
        data_size = av_get_bytes_per_sample(dec_ctx->sample_fmt);
        if (data_size < 0) {
            av_perr(data_size);
            return EXIT_FAILURE;
        }
        for (i = 0; i < frame->nb_samples; i++) {
            for (j = 0; j < dec_ctx->channels; j++) {
                fwrite(frame->data[j] + data_size * i, 1, data_size, outfile);
            }
        }
    }

    return EXIT_SUCCESS;
}

#define IS_NULL_PTR(ptr, message) \
    if (!ptr) { \
        fprintf(stderr, "\033[91m%s\033[0m\n", message); \
        goto FINALLY; \
    }
#define av_perr(errnum) \
    char av_err_buff[AV_ERROR_MAX_STRING_SIZE]; \
    av_strerror(errnum, (char *) &av_err_buff, AV_ERROR_MAX_STRING_SIZE); \
    fprintf(stderr, "\033[91m%s\033[0m\n", av_err_buff);

int main(int argc, char **argv) {
    const AVCodec *codec;
    AVCodecContext *c = nullptr;
    AVCodecParserContext *parser = nullptr;
    enum AVSampleFormat sfmt;

    int ret = 0, len = 0, n_channels = 0;
    FILE *source_file = nullptr, *target_file = nullptr;
    const char *fmt = nullptr;
    uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    uint8_t *data = nullptr;
    size_t data_size = 0;
    AVPacket *pkt = nullptr;
    AVFrame *decode_frame = nullptr;

    ...

    data = inbuf;
    data_size = fread(inbuf, 1, AUDIO_INBUF_SIZE, source_file);
    while (data_size > 0) {
        ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size, data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
        if (ret < 0) {
            fprintf(stderr, "\033[91mError while parsing\033[0m\n");
            goto FINALLY;
        }
        data += ret;
        data_size -= ret;
        if (pkt->size && decode(c, pkt, decode_frame, target_file)) goto FINALLY;

        if (data_size < AUDIO_REFILL_THRESH) {
            memmove(inbuf, data, data_size);
            data = inbuf;
            len = fread(data + data_size, 1, AUDIO_INBUF_SIZE - data_size, source_file);
            if (len > 0) data_size += len;
        }
    }
    ...
}


  


  I get these errors :

  


  [mp3float @ 0x55c51ac63440] Header missing
Invalid data found when processing input


  


  Here is the version of the ffmpeg library :

  


  libavutil      57. 17.100 / 57. 17.100
libavcodec     59. 18.100 / 59. 18.100
libavformat    59. 16.100 / 59. 16.100
libavdevice    59.  4.100 / 59.  4.100
libavfilter     8. 24.100 /  8. 24.100
libswscale      6.  4.100 /  6.  4.100
libswresample   4.  3.100 /  4.  3.100
libpostproc    56.  3.100 / 56.  3.100


  


  I guess this is due to the fundamental difference in the data format of the mp3 and mp2 frames, but I can't find a way to decode the mp3.

  


  What is the essential difference between the audio formats of mp3 and mp2 ? Also, what can I do to properly handle mp3 audio ?

  


• Merge commit ’6a10142faa1cca8ba2bfe51b970754f62d60f320’

  5 juillet 2013, par Michael Niedermayer

  Merge commit ’6a10142faa1cca8ba2bfe51b970754f62d60f320’
  * commit ’6a10142faa1cca8ba2bfe51b970754f62d60f320’ :
  
    indeo : reject negative array indexes
  Conflicts :
  
  	libavcodec/ivi_common.c
  See : 93927eb334dce961603645dd4ed9772bb2400cc4, a93c7ca6ef625188c9ec088c2e75f731b78c9923
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/ivi_common.c

• configure : simplify bigendian check

  27 mars 2024, par J. Dekker

  configure : simplify bigendian check
  The preferred way to use LTO is —enable-lto but often times packagers
  
  still end up with -flto in cflags for various reasons. Using grep
  
  on binary object files is brittle and relies on specific object
  
  representation, which in the case of LLVM bitcode, debug information or
  
  other intermediary formats can fail silently.
  This patch changes the check to a more commonly used define for GCC
  
  style compilers. More checks may be needed to cover other potential
  
  compilers that don't use the __BYTE_ORDER__ define.
  Signed-off-by : J. Dekker <jdek@itanimul.li>
  

  • [DH] configure