CODEWITHSUNDEEP
c++ffmpeg
cs guy
cs guy

Reputation: 939

ffmpeg Get Audio Samples in a specific AVSampleFormat from AVFrame

I am looking at the example from ffmpeg docs: Here

static int output_audio_frame(AVFrame *frame)
{
    size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(frame->format);
    printf("audio_frame n:%d nb_samples:%d pts:%s\n",
           audio_frame_count++, frame->nb_samples,
           av_ts2timestr(frame->pts, &audio_dec_ctx->time_base));
    /* Write the raw audio data samples of the first plane. This works
     * fine for packed formats (e.g. AV_SAMPLE_FMT_S16). However,
     * most audio decoders output planar audio, which uses a separate
     * plane of audio samples for each channel (e.g. AV_SAMPLE_FMT_S16P).
     * In other words, this code will write only the first audio channel
     * in these cases.
     * You should use libswresample or libavfilter to convert the frame
     * to packed data. */
    fwrite(frame->extended_data[0], 1, unpadded_linesize, audio_dst_file);
    return 0;
}

The issue is decoder's format cant be set so it will give me audio samples in any of the following types:

enum AVSampleFormat {
      AV_SAMPLE_FMT_NONE = -1, AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_S32,
      AV_SAMPLE_FMT_FLT, AV_SAMPLE_FMT_DBL, AV_SAMPLE_FMT_U8P, AV_SAMPLE_FMT_S16P,
      AV_SAMPLE_FMT_S32P, AV_SAMPLE_FMT_FLTP, AV_SAMPLE_FMT_DBLP, AV_SAMPLE_FMT_S64,
      AV_SAMPLE_FMT_S64P, AV_SAMPLE_FMT_NB
    }

I am working with a sound engine and the engine requres me to send float [-1 to 1] PCM data to the engine so I would like to obtain the frame's audio data as float for the two channels (stereo music). How may I do that? Do I need to use libswresample? If so can anyone sent me an example for my case

Upvotes: 0

Views: 978

Answers (1)

Erdal Küçük
Erdal Küçük

Reputation: 5858

If you don't get the desired format from the decoder, you have to resample it, encode with AV_SAMPLE_FMT_FLT.

According to enum AVSampleFormat

  • The floating-point formats are based on full volume being in the range [-1.0, 1.0]. Any values outside this range are beyond full volume level.

All the Examples are well documented and not that complicated. The function names alone are very explanatory, so it shouldn't be that hard to understand.

Upvotes: 1

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