Demonstrates swr_convert corruption of packed audio

resample-bug.c

#include <libavcodec/avcodec.h>
#include <libswresample/swresample.h>

int main(int argc, char* argv[]) {
    int r;
    int nb_samples = 10;
    int output_nb_samples = nb_samples;
    int nb_channels = av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO);
    int bytes_per_sample = av_get_bytes_per_sample(AV_SAMPLE_FMT_S16) * nb_channels;
    int bufsize = av_samples_get_buffer_size(NULL, nb_channels, nb_samples,
                                             AV_SAMPLE_FMT_S16, 1);
    int i;

    uint8_t inbuf[bufsize];
    uint8_t *input[] = { inbuf };
    uint8_t outbuf[bufsize];
    uint8_t *output[] = { outbuf };

    struct SwrContext* swr_ctx =
        swr_alloc_set_opts(NULL,
                           AV_CH_LAYOUT_STEREO,
                           AV_SAMPLE_FMT_S16,
                           44100,
                           AV_CH_LAYOUT_STEREO,
                           AV_SAMPLE_FMT_S16,
                           44100,
                           0, NULL);
    swr_init(swr_ctx);

    for (i = 0; i < sizeof(inbuf); i++)
        inbuf[i] = i;

    // Buffer input
    if ((r = swr_convert(swr_ctx, output, output_nb_samples / 2,
                         (const uint8_t**)input, nb_samples)) < 0)
        return -1;
    output[0] = &outbuf[r * bytes_per_sample];
    output_nb_samples -= r;

    // Drain buffer
    while ((r = swr_convert(swr_ctx, output, output_nb_samples, NULL, 0)) > 0) {
        output[0] = &outbuf[r * bytes_per_sample];
        output_nb_samples -= r;
    }

    // Resample should have been a straight copy
    for (i = 0; i < sizeof(inbuf); i++) {
        if (inbuf[i] != outbuf[i])
            fprintf(stderr, "Byte %d does not match %x != %x\n", i, inbuf[i], outbuf[i]);
    }
    fprintf(stderr, "Finished\n");
    return 0;
}