How to get bytearray from x264 frame writer?

Question

So here is libx264 FLV, MP4 and some other format file creators. in each format.c there is function called write_frame(). I want to get a bytearray of what it is writing to file. What shall be added to that functions for tham to return bytearray of what they try to write into file? (I would love to see example for FLV but if it'd work in general itd be grate!)

So there code for frame encoding in FLV looks like:

static int write_frame( hnd_t handle, uint8_t *p_nalu, int i_size, x264_picture_t *p_picture )
{
    flv_hnd_t *p_flv = handle;
    flv_buffer *c = p_flv->c;

    int64_t dts = (int64_t)( (p_picture->i_dts * 1000 * ((double)p_flv->i_timebase_num / p_flv->i_timebase_den)) + 0.5 );
    int64_t cts = (int64_t)( (p_picture->i_pts * 1000 * ((double)p_flv->i_timebase_num / p_flv->i_timebase_den)) + 0.5 );
    int64_t offset = cts - dts;

    if( p_flv->i_framenum )
    {
        int64_t prev_dts = (int64_t)( (p_flv->i_prev_dts * 1000 * ((double)p_flv->i_timebase_num / p_flv->i_timebase_den)) + 0.5 );
        int64_t prev_cts = (int64_t)( (p_flv->i_prev_pts * 1000 * ((double)p_flv->i_timebase_num / p_flv->i_timebase_den)) + 0.5 );
        if( prev_dts == dts )
        {
            double fps = ((double)p_flv->i_timebase_den / p_flv->i_timebase_num) / (p_picture->i_dts - p_flv->i_prev_dts);
            x264_cli_log( "flv", X264_LOG_WARNING, "duplicate DTS %"PRId64" generated by rounding\n"
                          "               current internal decoding framerate: %.6f fps\n", dts, fps );
        }
        if( prev_cts == cts )
        {
            double fps = ((double)p_flv->i_timebase_den / p_flv->i_timebase_num) / (p_picture->i_pts - p_flv->i_prev_pts);
            x264_cli_log( "flv", X264_LOG_WARNING, "duplicate CTS %"PRId64" generated by rounding\n"
                          "               current internal composition framerate: %.6f fps\n", cts, fps );
        }
    }
    p_flv->i_prev_dts = p_picture->i_dts;
    p_flv->i_prev_pts = p_picture->i_pts;

    // A new frame - write packet header
    x264_put_byte( c, FLV_TAG_TYPE_VIDEO );
    x264_put_be24( c, 0 ); // calculated later
    x264_put_be24( c, dts );
    x264_put_byte( c, dts >> 24 );
    x264_put_be24( c, 0 );

    p_flv->start = c->d_cur;
    x264_put_byte( c, p_picture->b_keyframe ? FLV_FRAME_KEY : FLV_FRAME_INTER );
    x264_put_byte( c, 1 ); // AVC NALU
    x264_put_be24( c, offset );

    if( p_flv->sei )
    {
        flv_append_data( c, p_flv->sei, p_flv->sei_len );
        free( p_flv->sei );
        p_flv->sei = NULL;
    }
    flv_append_data( c, p_nalu, i_size );

    unsigned length = c->d_cur - p_flv->start;
    rewrite_amf_be24( c, length, p_flv->start - 10 );
    x264_put_be32( c, 11 + length ); // Last tag size
    CHECK( flv_flush_data( c ) );

    p_flv->i_framenum++;

    return i_size;
}