gstreamer/subprojects/gst-plugins-good/ext/mpg123/gstmpg123audiodec.c

/*  MP3 decoding plugin for GStreamer using the mpg123 library
 *  Copyright (C) 2012 Carlos Rafael Giani
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/**
 * SECTION: element-mpg123audiodec
 * @see_also: lamemp3enc, mad
 *
 * Audio decoder for MPEG-1 layer 1/2/3 audio data.
 *
 * ## Example pipelines
 *
 * |[
 * gst-launch-1.0 filesrc location=music.mp3 ! mpegaudioparse ! mpg123audiodec ! audioconvert ! audioresample ! autoaudiosink
 * ]| Decode and play the mp3 file
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "gstmpg123audiodec.h"

#include <stdlib.h>
#include <string.h>

GST_DEBUG_CATEGORY_STATIC (mpg123_debug);
#define GST_CAT_DEFAULT mpg123_debug

/* Omitted sample formats that mpg123 supports (or at least can support):
 *  - 8bit integer signed
 *  - 8bit integer unsigned
 *  - a-law
 *  - mu-law
 *  - 64bit float
 *
 * The first four formats are not supported by the GstAudioDecoder base class.
 * (The internal gst_audio_format_from_caps_structure() call fails.)
 *
 * The 64bit float issue is tricky. mpg123 actually decodes to "real",
 * not necessarily to "float".
 *
 * "real" can be fixed point, 32bit float, 64bit float. There seems to be
 * no way how to find out which one of them is actually used.
 *
 * However, in all known installations, "real" equals 32bit float, so that's
 * what is used. */

static GstStaticPadTemplate static_sink_template =
GST_STATIC_PAD_TEMPLATE ("sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("audio/mpeg, "
        "mpegversion = (int) 1, "
        "layer = (int) [ 1, 3 ], "
        "rate = (int) { 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000 }, "
        "channels = (int) [ 1, 2 ], " "parsed = (boolean) true ")
    );

typedef struct
{
  guint64 clip_start, clip_end;
} GstMpg123AudioDecClipInfo;

static void gst_mpg123_audio_dec_dispose (GObject * object);
static gboolean gst_mpg123_audio_dec_start (GstAudioDecoder * dec);
static gboolean gst_mpg123_audio_dec_stop (GstAudioDecoder * dec);
static GstFlowReturn gst_mpg123_audio_dec_push_decoded_bytes (GstMpg123AudioDec
    * mpg123_decoder, unsigned char const *decoded_bytes,
    size_t num_decoded_bytes, guint64 clip_start, guint64 clip_end);
static GstFlowReturn gst_mpg123_audio_dec_handle_frame (GstAudioDecoder * dec,
    GstBuffer * input_buffer);
static gboolean gst_mpg123_audio_dec_set_format (GstAudioDecoder * dec,
    GstCaps * input_caps);
static void gst_mpg123_audio_dec_flush (GstAudioDecoder * dec, gboolean hard);

static void gst_mpg123_audio_dec_push_clip_info
    (GstMpg123AudioDec * mpg123_decoder, guint64 clip_start, guint64 clip_end);
static void gst_mpg123_audio_dec_pop_oldest_clip_info (GstMpg123AudioDec *
    mpg123_decoder, guint64 * clip_start, guint64 * clip_end);
static void gst_mpg123_audio_dec_clear_clip_info_queue (GstMpg123AudioDec *
    mpg123_decoder);
static guint gst_mpg123_audio_dec_get_info_queue_size (GstMpg123AudioDec *
    mpg123_decoder);

G_DEFINE_TYPE (GstMpg123AudioDec, gst_mpg123_audio_dec, GST_TYPE_AUDIO_DECODER);
GST_ELEMENT_REGISTER_DEFINE (mpg123audiodec, "mpg123audiodec",
    GST_RANK_PRIMARY, GST_TYPE_MPG123_AUDIO_DEC);

static void
gst_mpg123_audio_dec_class_init (GstMpg123AudioDecClass * klass)
{
  GObjectClass *object_class;
  GstAudioDecoderClass *base_class;
  GstElementClass *element_class;
  GstPadTemplate *src_template, *sink_template;
  int error;

  GST_DEBUG_CATEGORY_INIT (mpg123_debug, "mpg123", 0, "mpg123 mp3 decoder");

  object_class = G_OBJECT_CLASS (klass);
  base_class = GST_AUDIO_DECODER_CLASS (klass);
  element_class = GST_ELEMENT_CLASS (klass);

  gst_element_class_set_static_metadata (element_class,
      "mpg123 mp3 decoder",
      "Codec/Decoder/Audio",
      "Decodes mp3 streams using the mpg123 library",
      "Carlos Rafael Giani <dv@pseudoterminal.org>");

  /* Not using static pad template for srccaps, since the comma-separated list
   * of formats needs to be created depending on whatever mpg123 supports */
  {
    const int *format_list;
    const long *rates_list;
    size_t num, i;
    GString *s;
    GstCaps *src_template_caps;

    s = g_string_new ("audio/x-raw, ");

    mpg123_encodings (&format_list, &num);
    g_string_append (s, "format = { ");
    for (i = 0; i < num; ++i) {
      switch (format_list[i]) {
        case MPG123_ENC_SIGNED_16:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (S16));
          break;
        case MPG123_ENC_UNSIGNED_16:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (U16));
          break;
        case MPG123_ENC_SIGNED_24:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (S24));
          break;
        case MPG123_ENC_UNSIGNED_24:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (U24));
          break;
        case MPG123_ENC_SIGNED_32:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (S32));
          break;
        case MPG123_ENC_UNSIGNED_32:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (U32));
          break;
        case MPG123_ENC_FLOAT_32:
          g_string_append (s, (i > 0) ? ", " : "");
          g_string_append (s, GST_AUDIO_NE (F32));
          break;
        default:
          GST_DEBUG ("Ignoring mpg123 format %d", format_list[i]);
          break;
      }
    }
    g_string_append (s, " }, ");

    mpg123_rates (&rates_list, &num);
    g_string_append (s, "rate = (int) { ");
    for (i = 0; i < num; ++i) {
      g_string_append_printf (s, "%s%lu", (i > 0) ? ", " : "", rates_list[i]);
    }
    g_string_append (s, "}, ");

    g_string_append (s, "channels = (int) [ 1, 2 ], ");
    g_string_append (s, "layout = (string) interleaved");

    src_template_caps = gst_caps_from_string (s->str);
    src_template = gst_pad_template_new ("src", GST_PAD_SRC, GST_PAD_ALWAYS,
        src_template_caps);
    gst_caps_unref (src_template_caps);

    g_string_free (s, TRUE);
  }

  sink_template = gst_static_pad_template_get (&static_sink_template);

  gst_element_class_add_pad_template (element_class, sink_template);
  gst_element_class_add_pad_template (element_class, src_template);

  object_class->dispose = GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_dispose);
  base_class->start = GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_start);
  base_class->stop = GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_stop);
  base_class->handle_frame =
      GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_handle_frame);
  base_class->set_format = GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_set_format);
  base_class->flush = GST_DEBUG_FUNCPTR (gst_mpg123_audio_dec_flush);

  error = mpg123_init ();
  if (G_UNLIKELY (error != MPG123_OK))
    GST_ERROR ("Could not initialize mpg123 library: %s",
        mpg123_plain_strerror (error));
  else
    GST_INFO ("mpg123 library initialized");
}


void
gst_mpg123_audio_dec_init (GstMpg123AudioDec * mpg123_decoder)
{
  mpg123_decoder->handle = NULL;
  mpg123_decoder->audio_clip_info_queue =
      gst_vec_deque_new_for_struct (sizeof (GstMpg123AudioDecClipInfo), 16);

  gst_audio_decoder_set_needs_format (GST_AUDIO_DECODER (mpg123_decoder), TRUE);
  gst_audio_decoder_set_use_default_pad_acceptcaps (GST_AUDIO_DECODER_CAST
      (mpg123_decoder), TRUE);
  GST_PAD_SET_ACCEPT_TEMPLATE (GST_AUDIO_DECODER_SINK_PAD (mpg123_decoder));
}


static void
gst_mpg123_audio_dec_dispose (GObject * object)
{
  GstMpg123AudioDec *mpg123_decoder = GST_MPG123_AUDIO_DEC (object);

  if (mpg123_decoder->audio_clip_info_queue != NULL) {
    gst_vec_deque_free (mpg123_decoder->audio_clip_info_queue);
    mpg123_decoder->audio_clip_info_queue = NULL;
  }

  G_OBJECT_CLASS (gst_mpg123_audio_dec_parent_class)->dispose (object);
}


static gboolean
gst_mpg123_audio_dec_start (GstAudioDecoder * dec)
{
  GstMpg123AudioDec *mpg123_decoder;
  int error;

  mpg123_decoder = GST_MPG123_AUDIO_DEC (dec);
  error = 0;

  mpg123_decoder->handle = mpg123_new (NULL, &error);
  mpg123_decoder->has_next_audioinfo = FALSE;
  mpg123_decoder->frame_offset = 0;

  /* Initially, the mpg123 handle comes with a set of default formats
   * supported. This clears this set.  This is necessary, since only one
   * format shall be supported (see set_format for more). */
  mpg123_format_none (mpg123_decoder->handle);

  /* Built-in mpg123 support for gapless decoding is disabled for now,
   * since it does not work well with seeking */
  mpg123_param (mpg123_decoder->handle, MPG123_REMOVE_FLAGS, MPG123_GAPLESS, 0);
  /* Tells mpg123 to use a small read-ahead buffer for better MPEG sync;
   * essential for MP3 radio streams */
  mpg123_param (mpg123_decoder->handle, MPG123_ADD_FLAGS, MPG123_SEEKBUFFER, 0);
  /* Sets the resync limit to the end of the stream (otherwise mpg123 may give
   * up on decoding prematurely, especially with mp3 web radios) */
  mpg123_param (mpg123_decoder->handle, MPG123_RESYNC_LIMIT, -1, 0);
#if MPG123_API_VERSION >= 36
  /* The precise API version where MPG123_AUTO_RESAMPLE appeared is
   * somewhere between 29 and 36 */
  /* Don't let mpg123 resample output */
  mpg123_param (mpg123_decoder->handle, MPG123_REMOVE_FLAGS,
      MPG123_AUTO_RESAMPLE, 0);
#endif
  /* Don't let mpg123 print messages to stdout/stderr */
  mpg123_param (mpg123_decoder->handle, MPG123_ADD_FLAGS, MPG123_QUIET, 0);

  /* Open in feed mode (= encoded data is fed manually into the handle). */
  error = mpg123_open_feed (mpg123_decoder->handle);

  if (G_UNLIKELY (error != MPG123_OK)) {
    GST_ELEMENT_ERROR (dec, LIBRARY, INIT, (NULL),
        ("%s", mpg123_strerror (mpg123_decoder->handle)));
    mpg123_close (mpg123_decoder->handle);
    mpg123_delete (mpg123_decoder->handle);
    mpg123_decoder->handle = NULL;
    return FALSE;
  }

  GST_INFO_OBJECT (dec, "mpg123 decoder started");

  return TRUE;
}


static gboolean
gst_mpg123_audio_dec_stop (GstAudioDecoder * dec)
{
  GstMpg123AudioDec *mpg123_decoder = GST_MPG123_AUDIO_DEC (dec);

  if (G_LIKELY (mpg123_decoder->handle != NULL)) {
    mpg123_close (mpg123_decoder->handle);
    mpg123_delete (mpg123_decoder->handle);
    mpg123_decoder->handle = NULL;
  }

  gst_mpg123_audio_dec_clear_clip_info_queue (mpg123_decoder);

  GST_INFO_OBJECT (dec, "mpg123 decoder stopped");

  return TRUE;
}


static GstFlowReturn
gst_mpg123_audio_dec_push_decoded_bytes (GstMpg123AudioDec * mpg123_decoder,
    unsigned char const *decoded_bytes, size_t num_decoded_bytes,
    guint64 clip_start, guint64 clip_end)
{
  GstBuffer *output_buffer;
  GstAudioDecoder *dec;
  GstMapInfo info;

  output_buffer = NULL;
  dec = GST_AUDIO_DECODER (mpg123_decoder);

  if (G_UNLIKELY ((num_decoded_bytes == 0) || (decoded_bytes == NULL))) {
    /* This occurs in two cases:
     *
     * 1. The first few frames come in. These fill mpg123's buffers, and
     *    do not immediately yield decoded output. This stops once the
     *    mpg123_decode_frame () returns MPG123_NEW_FORMAT.
     * 2. The decoder is being drained.
     */
    return GST_FLOW_OK;
  }

  if (G_UNLIKELY (clip_start + clip_end >= num_decoded_bytes)) {
    /* Fully-clipped frames still need to be finished, since they got
     * decoded properly, they are just made of padding samples. */
    GST_LOG_OBJECT (mpg123_decoder, "frame is fully clipped; "
        "not pushing anything downstream");
    return gst_audio_decoder_finish_frame (dec, NULL, 1);
  }

  /* Apply clipping. */
  decoded_bytes += clip_start;
  num_decoded_bytes -= clip_start + clip_end;

  output_buffer = gst_audio_decoder_allocate_output_buffer (dec,
      num_decoded_bytes);

  if (gst_buffer_map (output_buffer, &info, GST_MAP_WRITE)) {
    memcpy (info.data, decoded_bytes, num_decoded_bytes);
    gst_buffer_unmap (output_buffer, &info);
  } else {
    GST_ERROR_OBJECT (mpg123_decoder, "gst_buffer_map() returned NULL");
    gst_buffer_unref (output_buffer);
    output_buffer = NULL;
  }

  return gst_audio_decoder_finish_frame (dec, output_buffer, 1);
}


static GstFlowReturn
gst_mpg123_audio_dec_handle_frame (GstAudioDecoder * dec,
    GstBuffer * input_buffer)
{
  GstMpg123AudioDec *mpg123_decoder;
  int decode_error;
  unsigned char *decoded_bytes;
  size_t num_decoded_bytes;
  GstFlowReturn retval;
  gboolean loop = TRUE;

  mpg123_decoder = GST_MPG123_AUDIO_DEC (dec);

  g_assert (mpg123_decoder->handle != NULL);

  /* Feed input data (if there is any) into mpg123. */
  if (G_LIKELY (input_buffer != NULL)) {
    GstMapInfo info;
    GstAudioClippingMeta *clipping_meta = NULL;

    /* Drop any Xing/LAME header as marked from the parser. It's not parsed in
     * this element and would decode to unnecessary silence samples. */
    if (GST_BUFFER_FLAG_IS_SET (input_buffer, GST_BUFFER_FLAG_DECODE_ONLY) &&
        GST_BUFFER_FLAG_IS_SET (input_buffer, GST_BUFFER_FLAG_DROPPABLE)) {
      return gst_audio_decoder_finish_frame (dec, NULL, 1);
    } else if (gst_buffer_map (input_buffer, &info, GST_MAP_READ)) {
      GST_LOG_OBJECT (mpg123_decoder, "got new MPEG audio frame with %"
          G_GSIZE_FORMAT " byte(s); feeding it into mpg123", info.size);
      mpg123_feed (mpg123_decoder->handle, info.data, info.size);
      gst_buffer_unmap (input_buffer, &info);
    } else {
      GST_AUDIO_DECODER_ERROR (mpg123_decoder, 1, RESOURCE, READ, (NULL),
          ("gst_memory_map() failed; could not feed MPEG frame into mpg123"),
          retval);
      return retval;
    }

    clipping_meta = gst_buffer_get_audio_clipping_meta (input_buffer);
    if (clipping_meta != NULL) {
      if (clipping_meta->format == GST_FORMAT_DEFAULT) {
        /* Get clipping info and convert it to bytes. */
        gint bpf = GST_AUDIO_INFO_BPF (&(mpg123_decoder->next_audioinfo));
        guint64 clip_start = clipping_meta->start * bpf;
        guint64 clip_end = clipping_meta->end * bpf;

        /* Push the clipping info into the queue. We cannot use clipping info
         * directly since mpg123 might not immediately be able to decode this
         * MPEG frame. In other words, it queues the frames internally. To
         * make sure we apply clipping properly, we therefore also have to
         * queue the clipping info accordingly. */
        gst_mpg123_audio_dec_push_clip_info (mpg123_decoder, clip_start,
            clip_end);

        GST_LOG_OBJECT (dec, "buffer has clipping metadata: start/end %"
            G_GUINT64_FORMAT "/%" G_GUINT64_FORMAT " samples (= %"
            G_GUINT64_FORMAT "/%" G_GUINT64_FORMAT " bytes); pushed it into "
            "audio clip info queue (now has %u item(s))", clipping_meta->start,
            clipping_meta->end, clip_start, clip_end,
            gst_mpg123_audio_dec_get_info_queue_size (mpg123_decoder));
      } else {
        gst_mpg123_audio_dec_push_clip_info (mpg123_decoder, 0, 0);
        GST_WARNING_OBJECT (dec,
            "buffer has clipping metadata in unsupported format %s",
            gst_format_get_name (clipping_meta->format));
      }
    } else {
      gst_mpg123_audio_dec_push_clip_info (mpg123_decoder, 0, 0);
    }
  } else {
    GST_LOG_OBJECT (dec, "got NULL pointer as input; "
        "will drain mpg123 decoder");
  }

  retval = GST_FLOW_OK;

  /* Keep trying to decode with mpg123 until it reports that,
   * it is done, needs more data, or an error occurs. */
  while (loop) {
    guint64 clip_start = 0, clip_end = 0;

    /* Try to decode a frame */
    decoded_bytes = NULL;
    num_decoded_bytes = 0;
#if MPG123_API_VERSION >= 48
    decode_error = mpg123_decode_frame64 (mpg123_decoder->handle,
        &mpg123_decoder->frame_offset, &decoded_bytes, &num_decoded_bytes);
#else
    decode_error = mpg123_decode_frame (mpg123_decoder->handle,
        &mpg123_decoder->frame_offset, &decoded_bytes, &num_decoded_bytes);
#endif

    if (G_LIKELY (decoded_bytes != NULL)) {
      gst_mpg123_audio_dec_pop_oldest_clip_info (mpg123_decoder, &clip_start,
          &clip_end);

      if ((clip_start + clip_end) > 0) {
        GST_LOG_OBJECT (dec, "retrieved clip info from queue; "
            "will clip %" G_GUINT64_FORMAT " byte(s) at the start and %"
            G_GUINT64_FORMAT " at the end of the decoded frame; queue now "
            "has %u item(s)", clip_start, clip_end,
            gst_mpg123_audio_dec_get_info_queue_size (mpg123_decoder));
      }

      GST_LOG_OBJECT (dec, "decoded %" G_GSIZE_FORMAT " byte(s)", (gsize)
          num_decoded_bytes);
    }

    switch (decode_error) {
      case MPG123_NEW_FORMAT:
        /* As mentioned in gst_mpg123_audio_dec_set_format(), the next audioinfo
         * is not set immediately; instead, the code waits for mpg123 to take
         * note of the new format, and then sets the audioinfo. This fixes glitches
         * with mp3s containing several format headers (for example, first half
         * using 44.1kHz, second half 32 kHz) */

        gst_mpg123_audio_dec_push_decoded_bytes (mpg123_decoder, decoded_bytes,
            num_decoded_bytes, clip_start, clip_end);

        GST_LOG_OBJECT (dec,
            "mpg123 reported a new format -> setting next srccaps");

        /* If there is a next audioinfo, use it, then set has_next_audioinfo to
         * FALSE, to make sure gst_audio_decoder_set_output_format() isn't called
         * again until set_format is called by the base class */
        if (mpg123_decoder->has_next_audioinfo) {
          if (!gst_audio_decoder_set_output_format (dec,
                  &(mpg123_decoder->next_audioinfo))) {
            GST_WARNING_OBJECT (dec, "Unable to set output format");
            retval = GST_FLOW_NOT_NEGOTIATED;
            loop = FALSE;
          }
          mpg123_decoder->has_next_audioinfo = FALSE;
        }

        break;

      case MPG123_NEED_MORE:
        loop = FALSE;
        GST_LOG_OBJECT (dec, "mpg123 needs more data to continue decoding");
        retval = gst_mpg123_audio_dec_push_decoded_bytes (mpg123_decoder,
            decoded_bytes, num_decoded_bytes, clip_start, clip_end);
        break;

      case MPG123_OK:
        retval = gst_mpg123_audio_dec_push_decoded_bytes (mpg123_decoder,
            decoded_bytes, num_decoded_bytes, clip_start, clip_end);
        break;

      case MPG123_DONE:
        /* If this happens, then the upstream parser somehow missed the ending
         * of the bitstream */
        gst_mpg123_audio_dec_push_decoded_bytes (mpg123_decoder, decoded_bytes,
            num_decoded_bytes, clip_start, clip_end);
        GST_LOG_OBJECT (dec, "mpg123 is done decoding");
        retval = GST_FLOW_EOS;
        loop = FALSE;
        break;

      default:
      {
        /* Anything else is considered an error */
        int errcode;

        /* use error by default */
        retval = GST_FLOW_ERROR;
        loop = FALSE;

        switch (decode_error) {
          case MPG123_ERR:
            errcode = mpg123_errcode (mpg123_decoder->handle);
            break;
          default:
            errcode = decode_error;
        }
        switch (errcode) {
          case MPG123_BAD_OUTFORMAT:{
            GstCaps *input_caps =
                gst_pad_get_current_caps (GST_AUDIO_DECODER_SINK_PAD (dec));
            GST_ELEMENT_ERROR (dec, STREAM, FORMAT, (NULL),
                ("Output sample format could not be used when trying to decode frame. "
                    "This is typically caused when the input caps (often the sample "
                    "rate) do not match the actual format of the audio data. "
                    "Input caps: %" GST_PTR_FORMAT, (gpointer) input_caps)
                );
            gst_caps_unref (input_caps);
            break;
          }
          default:{
            char const *errmsg = mpg123_plain_strerror (errcode);
            /* GST_AUDIO_DECODER_ERROR sets a new return value according to
             * its estimations */
            GST_AUDIO_DECODER_ERROR (mpg123_decoder, 1, STREAM, DECODE, (NULL),
                ("mpg123 decoding error: %s", errmsg), retval);
          }
        }
      }
    }
  }

  GST_LOG_OBJECT (mpg123_decoder, "done handling frame");

  return retval;
}


static gboolean
gst_mpg123_audio_dec_set_format (GstAudioDecoder * dec, GstCaps * input_caps)
{
  /* "encoding" is the sample format specifier for mpg123 */
  int encoding;
  int sample_rate, num_channels;
  GstAudioFormat format;
  GstMpg123AudioDec *mpg123_decoder;
  gboolean retval = FALSE;

  mpg123_decoder = GST_MPG123_AUDIO_DEC (dec);

  g_assert (mpg123_decoder->handle != NULL);

  mpg123_decoder->has_next_audioinfo = FALSE;

  /* Get sample rate and number of channels from input_caps */
  {
    GstStructure *structure;
    gboolean err = FALSE;

    /* Only the first structure is used (multiple
     * input caps structures don't make sense */
    structure = gst_caps_get_structure (input_caps, 0);

    if (!gst_structure_get_int (structure, "rate", &sample_rate)) {
      err = TRUE;
      GST_ERROR_OBJECT (dec, "Input caps do not have a rate value");
    }
    if (!gst_structure_get_int (structure, "channels", &num_channels)) {
      err = TRUE;
      GST_ERROR_OBJECT (dec, "Input caps do not have a channel value");
    }

    if (G_UNLIKELY (err))
      goto done;
  }

  /* Get sample format from the allowed src caps */
  {
    GstCaps *allowed_srccaps =
        gst_pad_get_allowed_caps (GST_AUDIO_DECODER_SRC_PAD (dec));

    if (allowed_srccaps == NULL) {
      /* srcpad is not linked (yet), so no peer information is available;
       * just use the default sample format (16 bit signed integer) */
      GST_DEBUG_OBJECT (mpg123_decoder,
          "srcpad is not linked (yet) -> using S16 sample format");
      format = GST_AUDIO_FORMAT_S16;
      encoding = MPG123_ENC_SIGNED_16;
    } else if (gst_caps_is_empty (allowed_srccaps)) {
      gst_caps_unref (allowed_srccaps);
      goto done;
    } else {
      gchar const *format_str;
      GValue const *format_value;

      /* Look at the sample format values from the first structure */
      GstStructure *structure = gst_caps_get_structure (allowed_srccaps, 0);
      format_value = gst_structure_get_value (structure, "format");

      if (format_value == NULL) {
        gst_caps_unref (allowed_srccaps);
        goto done;
      } else if (GST_VALUE_HOLDS_LIST (format_value)) {
        /* if value is a format list, pick the first entry */
        GValue const *fmt_list_value =
            gst_value_list_get_value (format_value, 0);
        format_str = g_value_get_string (fmt_list_value);
      } else if (G_VALUE_HOLDS_STRING (format_value)) {
        /* if value is a string, use it directly */
        format_str = g_value_get_string (format_value);
      } else {
        GST_ERROR_OBJECT (mpg123_decoder, "unexpected type for 'format' field "
            "in caps structure %" GST_PTR_FORMAT, (gpointer) structure);
        gst_caps_unref (allowed_srccaps);
        goto done;
      }

      /* get the format value from the string */
      format = gst_audio_format_from_string (format_str);
      gst_caps_unref (allowed_srccaps);

      g_assert (format != GST_AUDIO_FORMAT_UNKNOWN);

      /* convert format to mpg123 encoding */
      switch (format) {
        case GST_AUDIO_FORMAT_S16:
          encoding = MPG123_ENC_SIGNED_16;
          break;
        case GST_AUDIO_FORMAT_S24:
          encoding = MPG123_ENC_SIGNED_24;
          break;
        case GST_AUDIO_FORMAT_S32:
          encoding = MPG123_ENC_SIGNED_32;
          break;
        case GST_AUDIO_FORMAT_U16:
          encoding = MPG123_ENC_UNSIGNED_16;
          break;
        case GST_AUDIO_FORMAT_U24:
          encoding = MPG123_ENC_UNSIGNED_24;
          break;
        case GST_AUDIO_FORMAT_U32:
          encoding = MPG123_ENC_UNSIGNED_32;
          break;
        case GST_AUDIO_FORMAT_F32:
          encoding = MPG123_ENC_FLOAT_32;
          break;
        default:
          g_assert_not_reached ();
          goto done;
      }
    }
  }

  /* Sample rate, number of channels, and sample format are known at this point.
   * Set the audioinfo structure's values and the mpg123 format. */
  {
    int err;

    /* clear all existing format settings from the mpg123 instance */
    mpg123_format_none (mpg123_decoder->handle);
    /* set the chosen format */
    err =
        mpg123_format (mpg123_decoder->handle, sample_rate, num_channels,
        encoding);

    if (err != MPG123_OK) {
      GST_WARNING_OBJECT (dec,
          "mpg123_format() failed: %s",
          mpg123_strerror (mpg123_decoder->handle));
    } else {
      gst_audio_info_init (&(mpg123_decoder->next_audioinfo));
      gst_audio_info_set_format (&(mpg123_decoder->next_audioinfo), format,
          sample_rate, num_channels, NULL);
      GST_LOG_OBJECT (dec, "The next audio format is: %s, %u Hz, %u channels",
          gst_audio_format_to_string (format), sample_rate, num_channels);
      mpg123_decoder->has_next_audioinfo = TRUE;

      retval = TRUE;
    }
  }

done:
  return retval;
}


static void
gst_mpg123_audio_dec_flush (GstAudioDecoder * dec, gboolean hard)
{
  int error;
  GstMpg123AudioDec *mpg123_decoder;

  GST_LOG_OBJECT (dec, "Flushing decoder");

  mpg123_decoder = GST_MPG123_AUDIO_DEC (dec);

  g_assert (mpg123_decoder->handle != NULL);

  /* Flush by reopening the feed */
  mpg123_close (mpg123_decoder->handle);
  error = mpg123_open_feed (mpg123_decoder->handle);

  if (G_UNLIKELY (error != MPG123_OK)) {
    GST_ELEMENT_ERROR (dec, LIBRARY, INIT, (NULL),
        ("Error while reopening mpg123 feed: %s",
            mpg123_plain_strerror (error)));
    mpg123_close (mpg123_decoder->handle);
    mpg123_delete (mpg123_decoder->handle);
    mpg123_decoder->handle = NULL;
  }

  if (hard)
    mpg123_decoder->has_next_audioinfo = FALSE;

  gst_mpg123_audio_dec_clear_clip_info_queue (mpg123_decoder);

  /* opening/closing feeds do not affect the format defined by the
   * mpg123_format() call that was made in gst_mpg123_audio_dec_set_format(),
   * and since the up/downstream caps are not expected to change here, no
   * mpg123_format() calls are done */
}


static void gst_mpg123_audio_dec_push_clip_info
    (GstMpg123AudioDec * mpg123_decoder, guint64 clip_start, guint64 clip_end)
{
  GstMpg123AudioDecClipInfo clip_info = { clip_start, clip_end };
  gst_vec_deque_push_tail_struct (mpg123_decoder->audio_clip_info_queue,
      &clip_info);
}


static void
gst_mpg123_audio_dec_pop_oldest_clip_info (GstMpg123AudioDec *
    mpg123_decoder, guint64 * clip_start, guint64 * clip_end)
{
  guint queue_length;
  GstMpg123AudioDecClipInfo *clip_info;

  queue_length = gst_mpg123_audio_dec_get_info_queue_size (mpg123_decoder);
  if (queue_length == 0)
    return;

  clip_info =
      gst_vec_deque_pop_head_struct (mpg123_decoder->audio_clip_info_queue);

  *clip_start = clip_info->clip_start;
  *clip_end = clip_info->clip_end;
}

static void
gst_mpg123_audio_dec_clear_clip_info_queue (GstMpg123AudioDec * mpg123_decoder)
{
  gst_vec_deque_clear (mpg123_decoder->audio_clip_info_queue);
}


static guint
gst_mpg123_audio_dec_get_info_queue_size (GstMpg123AudioDec * mpg123_decoder)
{
  return gst_vec_deque_get_length (mpg123_decoder->audio_clip_info_queue);
}

static gboolean
plugin_init (GstPlugin * plugin)
{
  return GST_ELEMENT_REGISTER (mpg123audiodec, plugin);
}

GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
    GST_VERSION_MINOR,
    mpg123, "mp3 decoding based on the mpg123 library",
    plugin_init, VERSION, "LGPL", GST_PACKAGE_NAME, GST_PACKAGE_ORIGIN)