/*

  * IEC 61937 muxer

  * Copyright (c) 2009 Bartlomiej Wolowiec

  * Copyright (c) 2010 Anssi Hannula
  * Copyright (c) 2010 Carl Eugen Hoyos

  *
  * This file is part of FFmpeg.
  *
  * FFmpeg 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.
  *
  * FFmpeg 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 FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file

  * IEC-61937 encapsulation of various formats, used by S/PDIF
  * @author Bartlomiej Wolowiec

  * @author Anssi Hannula
  * @author Carl Eugen Hoyos

  */
 
 /*
  * Terminology used in specification:

  * data-burst - IEC61937 frame, contains header and encapsuled frame

  * burst-preamble - IEC61937 frame header, contains 16-bit words named Pa, Pb, Pc and Pd

  * burst-payload - encapsuled frame
  * Pa, Pb - syncword - 0xF872, 0x4E1F
  * Pc - burst-info, contains data-type (bits 0-6), error flag (bit 7), data-type-dependent info (bits 8-12)
  *      and bitstream number (bits 13-15)
  * data-type - determines type of encapsuled frames
  * Pd - length code (number of bits or bytes of encapsuled frame - according to data_type)
  *

  * IEC 61937 frames at normal usage start every specific count of bytes,

  *      dependent from data-type (spaces between packets are filled by zeros)
  */
 

 #include <inttypes.h>
 

 #include "avformat.h"

 #include "avio_internal.h"

 #include "spdif.h"

 #include "libavcodec/ac3.h"

 #include "libavcodec/adts_parser.h"

 #include "libavcodec/dca.h"

 #include "libavcodec/dca_syncwords.h"

 #include "libavutil/opt.h"

 typedef struct IEC61937Context {

     const AVClass *av_class;

     enum IEC61937DataType data_type;///< burst info - reference to type of payload of the data-burst

     int length_code;                ///< length code in bits or bytes, depending on data type

     int pkt_offset;                 ///< data burst repetition period in bytes
     uint8_t *buffer;                ///< allocated buffer, used for swap bytes
     int buffer_size;                ///< size of allocated buffer
 

     uint8_t *out_buf;               ///< pointer to the outgoing data before byte-swapping
     int out_bytes;                  ///< amount of outgoing bytes
 

     int use_preamble;               ///< preamble enabled (disabled for exactly pre-padded DTS)

     int extra_bswap;                ///< extra bswap for payload (for LE DTS => standard BE DTS)
 

     uint8_t *hd_buf;                ///< allocated buffer to concatenate hd audio frames
     int hd_buf_size;                ///< size of the hd audio buffer
     int hd_buf_count;               ///< number of frames in the hd audio buffer
     int hd_buf_filled;              ///< amount of bytes in the hd audio buffer
 

     int dtshd_skip;                 ///< counter used for skipping DTS-HD frames
 
     /* AVOptions: */
     int dtshd_rate;
     int dtshd_fallback;

 #define SPDIF_FLAG_BIGENDIAN    0x01
     int spdif_flags;

     /// function, which generates codec dependent header information.

     /// Sets data_type and pkt_offset, and length_code, out_bytes, out_buf if necessary

     int (*header_info) (AVFormatContext *s, AVPacket *pkt);

 } IEC61937Context;

 static const AVOption options[] = {

 { "spdif_flags", "IEC 61937 encapsulation flags", offsetof(IEC61937Context, spdif_flags), AV_OPT_TYPE_FLAGS, {.i64 = 0}, 0, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "spdif_flags" },

 { "be", "output in big-endian format (for use as s16be)", 0, AV_OPT_TYPE_CONST, {.i64 = SPDIF_FLAG_BIGENDIAN},  0, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "spdif_flags" },

 { "dtshd_rate", "mux complete DTS frames in HD mode at the specified IEC958 rate (in Hz, default 0=disabled)", offsetof(IEC61937Context, dtshd_rate), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 768000, AV_OPT_FLAG_ENCODING_PARAM },
 { "dtshd_fallback_time", "min secs to strip HD for after an overflow (-1: till the end, default 60)", offsetof(IEC61937Context, dtshd_fallback), AV_OPT_TYPE_INT, {.i64 = 60}, -1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },

 { NULL },
 };
 

 static const AVClass spdif_class = {

     .class_name     = "spdif",
     .item_name      = av_default_item_name,
     .option         = options,
     .version        = LIBAVUTIL_VERSION_INT,
 };

 
 static int spdif_header_ac3(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     int bitstream_mode = pkt->data[5] & 0x7;

     ctx->data_type  = IEC61937_AC3 | (bitstream_mode << 8);

     ctx->pkt_offset = AC3_FRAME_SIZE << 2;
     return 0;
 }
 

 static int spdif_header_eac3(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     static const uint8_t eac3_repeat[4] = {6, 3, 2, 1};
     int repeat = 1;
 

     int bsid = pkt->data[5] >> 3;
     if (bsid > 10 && (pkt->data[4] & 0xc0) != 0xc0) /* fscod */

         repeat = eac3_repeat[(pkt->data[4] & 0x30) >> 4]; /* numblkscod */
 
     ctx->hd_buf = av_fast_realloc(ctx->hd_buf, &ctx->hd_buf_size, ctx->hd_buf_filled + pkt->size);
     if (!ctx->hd_buf)
         return AVERROR(ENOMEM);
 
     memcpy(&ctx->hd_buf[ctx->hd_buf_filled], pkt->data, pkt->size);
 
     ctx->hd_buf_filled += pkt->size;
     if (++ctx->hd_buf_count < repeat){
         ctx->pkt_offset = 0;
         return 0;
     }

     ctx->data_type   = IEC61937_EAC3;

     ctx->pkt_offset  = 24576;
     ctx->out_buf     = ctx->hd_buf;
     ctx->out_bytes   = ctx->hd_buf_filled;
     ctx->length_code = ctx->hd_buf_filled;
 
     ctx->hd_buf_count  = 0;
     ctx->hd_buf_filled = 0;
     return 0;
 }
 

 /*
  * DTS type IV (DTS-HD) can be transmitted with various frame repetition
  * periods; longer repetition periods allow for longer packets and therefore
  * higher bitrate. Longer repetition periods mean that the constant bitrate of

  * the output IEC 61937 stream is higher.

  * The repetition period is measured in IEC 60958 frames (4 bytes).
  */
 static int spdif_dts4_subtype(int period)
 {
     switch (period) {

     case 512:   return 0x0;
     case 1024:  return 0x1;
     case 2048:  return 0x2;
     case 4096:  return 0x3;
     case 8192:  return 0x4;
     case 16384: return 0x5;

     }
     return -1;
 }
 
 static int spdif_header_dts4(AVFormatContext *s, AVPacket *pkt, int core_size,
                              int sample_rate, int blocks)
 {
     IEC61937Context *ctx = s->priv_data;
     static const char dtshd_start_code[10] = { 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xfe, 0xfe };
     int pkt_size = pkt->size;
     int period;
     int subtype;
 
     if (!core_size) {
         av_log(s, AV_LOG_ERROR, "HD mode not supported for this format\n");
         return AVERROR(EINVAL);
     }
 
     if (!sample_rate) {
         av_log(s, AV_LOG_ERROR, "Unknown DTS sample rate for HD\n");
         return AVERROR_INVALIDDATA;
     }
 
     period = ctx->dtshd_rate * (blocks << 5) / sample_rate;
     subtype = spdif_dts4_subtype(period);
 
     if (subtype < 0) {
         av_log(s, AV_LOG_ERROR, "Specified HD rate of %d Hz would require an "
                "impossible repetition period of %d for the current DTS stream"
                " (blocks = %d, sample rate = %d)\n", ctx->dtshd_rate, period,
                blocks << 5, sample_rate);
         return AVERROR(EINVAL);
     }
 
     /* set pkt_offset and DTS IV subtype according to the requested output
      * rate */
     ctx->pkt_offset = period * 4;
     ctx->data_type = IEC61937_DTSHD | subtype << 8;
 
     /* If the bitrate is too high for transmitting at the selected
      * repetition period setting, strip DTS-HD until a good amount
      * of consecutive non-overflowing HD frames have been observed.
      * This generally only happens if the caller is cramming a Master
      * Audio stream into 192kHz IEC 60958 (which may or may not fit). */
     if (sizeof(dtshd_start_code) + 2 + pkt_size
             > ctx->pkt_offset - BURST_HEADER_SIZE && core_size) {
         if (!ctx->dtshd_skip)
             av_log(s, AV_LOG_WARNING, "DTS-HD bitrate too high, "
                                       "temporarily sending core only\n");
         if (ctx->dtshd_fallback > 0)
             ctx->dtshd_skip = sample_rate * ctx->dtshd_fallback / (blocks << 5);
         else

             /* skip permanently (dtshd_fallback == -1) or just once
              * (dtshd_fallback == 0) */

             ctx->dtshd_skip = 1;
     }
     if (ctx->dtshd_skip && core_size) {
         pkt_size = core_size;
         if (ctx->dtshd_fallback >= 0)
             --ctx->dtshd_skip;
     }
 
     ctx->out_bytes   = sizeof(dtshd_start_code) + 2 + pkt_size;

 
     /* Align so that (length_code & 0xf) == 0x8. This is reportedly needed
      * with some receivers, but the exact requirement is unconfirmed. */
     ctx->length_code = FFALIGN(ctx->out_bytes + 0x8, 0x10) - 0x8;

     av_fast_malloc(&ctx->hd_buf, &ctx->hd_buf_size, ctx->out_bytes);

     if (!ctx->hd_buf)
         return AVERROR(ENOMEM);
 
     ctx->out_buf = ctx->hd_buf;
 
     memcpy(ctx->hd_buf, dtshd_start_code, sizeof(dtshd_start_code));
     AV_WB16(ctx->hd_buf + sizeof(dtshd_start_code), pkt_size);
     memcpy(ctx->hd_buf + sizeof(dtshd_start_code) + 2, pkt->data, pkt_size);
 
     return 0;
 }
 

 static int spdif_header_dts(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     uint32_t syncword_dts = AV_RB32(pkt->data);
     int blocks;

     int sample_rate = 0;
     int core_size = 0;
 
     if (pkt->size < 9)
         return AVERROR_INVALIDDATA;

 
     switch (syncword_dts) {

     case DCA_SYNCWORD_CORE_BE:

         blocks = (AV_RB16(pkt->data + 4) >> 2) & 0x7f;

         core_size = ((AV_RB24(pkt->data + 5) >> 4) & 0x3fff) + 1;

         sample_rate = avpriv_dca_sample_rates[(pkt->data[8] >> 2) & 0x0f];

         break;

     case DCA_SYNCWORD_CORE_LE:

         blocks = (AV_RL16(pkt->data + 4) >> 2) & 0x7f;

         ctx->extra_bswap = 1;

         break;

     case DCA_SYNCWORD_CORE_14B_BE:

         blocks =
             (((pkt->data[5] & 0x07) << 4) | ((pkt->data[6] & 0x3f) >> 2));
         break;

     case DCA_SYNCWORD_CORE_14B_LE:

         blocks =
             (((pkt->data[4] & 0x07) << 4) | ((pkt->data[7] & 0x3f) >> 2));

         ctx->extra_bswap = 1;

         break;

     case DCA_SYNCWORD_SUBSTREAM:

         /* We only handle HD frames that are paired with core. However,
            sometimes DTS-HD streams with core have a stray HD frame without
            core in the beginning of the stream. */
         av_log(s, AV_LOG_ERROR, "stray DTS-HD frame\n");
         return AVERROR_INVALIDDATA;

     default:

         av_log(s, AV_LOG_ERROR, "bad DTS syncword 0x%"PRIx32"\n", syncword_dts);

         return AVERROR_INVALIDDATA;

     }
     blocks++;

 
     if (ctx->dtshd_rate)
         /* DTS type IV output requested */
         return spdif_header_dts4(s, pkt, core_size, sample_rate, blocks);
 

     switch (blocks) {

     case  512 >> 5: ctx->data_type = IEC61937_DTS1; break;
     case 1024 >> 5: ctx->data_type = IEC61937_DTS2; break;
     case 2048 >> 5: ctx->data_type = IEC61937_DTS3; break;

     default:
         av_log(s, AV_LOG_ERROR, "%i samples in DTS frame not supported\n",
                blocks << 5);

         return AVERROR(ENOSYS);

     }

 
     /* discard extraneous data by default */
     if (core_size && core_size < pkt->size) {
         ctx->out_bytes = core_size;
         ctx->length_code = core_size << 3;
     }
 

     ctx->pkt_offset = blocks << 7;
 

     if (ctx->out_bytes == ctx->pkt_offset) {
         /* The DTS stream fits exactly into the output stream, so skip the
          * preamble as it would not fit in there. This is the case for dts
          * discs and dts-in-wav. */
         ctx->use_preamble = 0;

     } else if (ctx->out_bytes > ctx->pkt_offset - BURST_HEADER_SIZE) {

         avpriv_request_sample(s, "Unrecognized large DTS frame");

         /* This will fail with a "bitrate too high" in the caller */

     }
 

     return 0;
 }
 

 static const enum IEC61937DataType mpeg_data_type[2][3] = {

     //     LAYER1                      LAYER2                  LAYER3

     { IEC61937_MPEG2_LAYER1_LSF, IEC61937_MPEG2_LAYER2_LSF, IEC61937_MPEG2_LAYER3_LSF }, // MPEG-2 LSF
     { IEC61937_MPEG1_LAYER1,     IEC61937_MPEG1_LAYER23,    IEC61937_MPEG1_LAYER23 },    // MPEG-1

 };
 
 static int spdif_header_mpeg(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     int version =      (pkt->data[1] >> 3) & 3;
     int layer   = 3 - ((pkt->data[1] >> 1) & 3);
     int extension = pkt->data[2] & 1;
 
     if (layer == 3 || version == 1) {
         av_log(s, AV_LOG_ERROR, "Wrong MPEG file format\n");

         return AVERROR_INVALIDDATA;

     }
     av_log(s, AV_LOG_DEBUG, "version: %i layer: %i extension: %i\n", version, layer, extension);
     if (version == 2 && extension) {

         ctx->data_type  = IEC61937_MPEG2_EXT;

         ctx->pkt_offset = 4608;
     } else {
         ctx->data_type  = mpeg_data_type [version & 1][layer];

         ctx->pkt_offset = spdif_mpeg_pkt_offset[version & 1][layer];

     }

     // TODO Data type dependent info (normal/karaoke, dynamic range control)

     return 0;
 }
 
 static int spdif_header_aac(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     uint32_t samples;
     uint8_t frames;

     int ret;
 

     ret = av_adts_header_parse(pkt->data, &samples, &frames);

     if (ret < 0) {
         av_log(s, AV_LOG_ERROR, "Wrong AAC file format\n");

         return ret;

     }
 

     ctx->pkt_offset = samples << 2;
     switch (frames) {

     case 1:

         ctx->data_type = IEC61937_MPEG2_AAC;

         break;
     case 2:

         ctx->data_type = IEC61937_MPEG2_AAC_LSF_2048;

         break;
     case 4:

         ctx->data_type = IEC61937_MPEG2_AAC_LSF_4096;

         break;
     default:

         av_log(s, AV_LOG_ERROR,

                "%"PRIu32" samples in AAC frame not supported\n", samples);

         return AVERROR(EINVAL);

     }
     //TODO Data type dependent info (LC profile/SBR)
     return 0;
 }
 

 
 /*
  * It seems Dolby TrueHD frames have to be encapsulated in MAT frames before
  * they can be encapsulated in IEC 61937.
  * Here we encapsulate 24 TrueHD frames in a single MAT frame, padding them
  * to achieve constant rate.
  * The actual format of a MAT frame is unknown, but the below seems to work.
  * However, it seems it is not actually necessary for the 24 TrueHD frames to
  * be in an exact alignment with the MAT frame.
  */
 #define MAT_FRAME_SIZE          61424
 #define TRUEHD_FRAME_OFFSET     2560
 #define MAT_MIDDLE_CODE_OFFSET  -4
 
 static int spdif_header_truehd(AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     int mat_code_length = 0;

     static const char mat_end_code[16] = { 0xC3, 0xC2, 0xC0, 0xC4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x97, 0x11 };

 
     if (!ctx->hd_buf_count) {

         static const char mat_start_code[20] = { 0x07, 0x9E, 0x00, 0x03, 0x84, 0x01, 0x01, 0x01, 0x80, 0x00, 0x56, 0xA5, 0x3B, 0xF4, 0x81, 0x83, 0x49, 0x80, 0x77, 0xE0 };

         mat_code_length = sizeof(mat_start_code) + BURST_HEADER_SIZE;
         memcpy(ctx->hd_buf, mat_start_code, sizeof(mat_start_code));
 
     } else if (ctx->hd_buf_count == 12) {

         static const char mat_middle_code[12] = { 0xC3, 0xC1, 0x42, 0x49, 0x3B, 0xFA, 0x82, 0x83, 0x49, 0x80, 0x77, 0xE0 };

         mat_code_length = sizeof(mat_middle_code) + MAT_MIDDLE_CODE_OFFSET;
         memcpy(&ctx->hd_buf[12 * TRUEHD_FRAME_OFFSET - BURST_HEADER_SIZE + MAT_MIDDLE_CODE_OFFSET],
                mat_middle_code, sizeof(mat_middle_code));
     }
 
     if (pkt->size > TRUEHD_FRAME_OFFSET - mat_code_length) {
         /* if such frames exist, we'd need some more complex logic to
          * distribute the TrueHD frames in the MAT frame */

         avpriv_request_sample(s, "Too large TrueHD frame of %d bytes",
                               pkt->size);

         return AVERROR_PATCHWELCOME;

     }
 
     memcpy(&ctx->hd_buf[ctx->hd_buf_count * TRUEHD_FRAME_OFFSET - BURST_HEADER_SIZE + mat_code_length],
            pkt->data, pkt->size);
     memset(&ctx->hd_buf[ctx->hd_buf_count * TRUEHD_FRAME_OFFSET - BURST_HEADER_SIZE + mat_code_length + pkt->size],
            0, TRUEHD_FRAME_OFFSET - pkt->size - mat_code_length);
 
     if (++ctx->hd_buf_count < 24){
         ctx->pkt_offset = 0;
         return 0;
     }
     memcpy(&ctx->hd_buf[MAT_FRAME_SIZE - sizeof(mat_end_code)], mat_end_code, sizeof(mat_end_code));
     ctx->hd_buf_count = 0;
 

     ctx->data_type   = IEC61937_TRUEHD;

     ctx->pkt_offset  = 61440;
     ctx->out_buf     = ctx->hd_buf;
     ctx->out_bytes   = MAT_FRAME_SIZE;
     ctx->length_code = MAT_FRAME_SIZE;
     return 0;
 }
 

 static int spdif_write_header(AVFormatContext *s)
 {

     IEC61937Context *ctx = s->priv_data;

     switch (s->streams[0]->codecpar->codec_id) {

     case AV_CODEC_ID_AC3:

         ctx->header_info = spdif_header_ac3;
         break;

     case AV_CODEC_ID_EAC3:

         ctx->header_info = spdif_header_eac3;
         break;

     case AV_CODEC_ID_MP1:
     case AV_CODEC_ID_MP2:
     case AV_CODEC_ID_MP3:

         ctx->header_info = spdif_header_mpeg;
         break;

     case AV_CODEC_ID_DTS:

         ctx->header_info = spdif_header_dts;
         break;

     case AV_CODEC_ID_AAC:

         ctx->header_info = spdif_header_aac;
         break;

     case AV_CODEC_ID_TRUEHD:

     case AV_CODEC_ID_MLP:

         ctx->header_info = spdif_header_truehd;
         ctx->hd_buf = av_malloc(MAT_FRAME_SIZE);
         if (!ctx->hd_buf)
             return AVERROR(ENOMEM);
         break;

     default:

         avpriv_report_missing_feature(s, "Codec %d",
                                       s->streams[0]->codecpar->codec_id);

         return AVERROR_PATCHWELCOME;

     }
     return 0;
 }
 
 static int spdif_write_trailer(AVFormatContext *s)
 {

     IEC61937Context *ctx = s->priv_data;

     av_freep(&ctx->buffer);

     av_freep(&ctx->hd_buf);

     return 0;
 }
 

 static av_always_inline void spdif_put_16(IEC61937Context *ctx,

                                           AVIOContext *pb, unsigned int val)

 {
     if (ctx->spdif_flags & SPDIF_FLAG_BIGENDIAN)

         avio_wb16(pb, val);

     else

         avio_wl16(pb, val);

 }
 

 static int spdif_write_packet(struct AVFormatContext *s, AVPacket *pkt)
 {

     IEC61937Context *ctx = s->priv_data;

     int ret, padding;
 

     ctx->out_buf = pkt->data;

     ctx->out_bytes = pkt->size;
     ctx->length_code = FFALIGN(pkt->size, 2) << 3;

     ctx->use_preamble = 1;

     ctx->extra_bswap = 0;

     ret = ctx->header_info(s, pkt);
     if (ret < 0)

         return ret;

     if (!ctx->pkt_offset)
         return 0;

     padding = (ctx->pkt_offset - ctx->use_preamble * BURST_HEADER_SIZE - ctx->out_bytes) & ~1;

     if (padding < 0) {
         av_log(s, AV_LOG_ERROR, "bitrate is too high\n");

         return AVERROR(EINVAL);

     }
 

     if (ctx->use_preamble) {

         spdif_put_16(ctx, s->pb, SYNCWORD1);       //Pa
         spdif_put_16(ctx, s->pb, SYNCWORD2);       //Pb
         spdif_put_16(ctx, s->pb, ctx->data_type);  //Pc
         spdif_put_16(ctx, s->pb, ctx->length_code);//Pd

     }

     if (ctx->extra_bswap ^ (ctx->spdif_flags & SPDIF_FLAG_BIGENDIAN)) {

         avio_write(s->pb, ctx->out_buf, ctx->out_bytes & ~1);

     } else {

         av_fast_malloc(&ctx->buffer, &ctx->buffer_size, ctx->out_bytes + AV_INPUT_BUFFER_PADDING_SIZE);

         if (!ctx->buffer)
             return AVERROR(ENOMEM);
         ff_spdif_bswap_buf16((uint16_t *)ctx->buffer, (uint16_t *)ctx->out_buf, ctx->out_bytes >> 1);
         avio_write(s->pb, ctx->buffer, ctx->out_bytes & ~1);

     }

     /* a final lone byte has to be MSB aligned */

     if (ctx->out_bytes & 1)

         spdif_put_16(ctx, s->pb, ctx->out_buf[ctx->out_bytes - 1] << 8);

     ffio_fill(s->pb, 0, padding);

 
     av_log(s, AV_LOG_DEBUG, "type=%x len=%i pkt_offset=%i\n",

            ctx->data_type, ctx->out_bytes, ctx->pkt_offset);

 
     return 0;
 }
 

 AVOutputFormat ff_spdif_muxer = {

     .name              = "spdif",
     .long_name         = NULL_IF_CONFIG_SMALL("IEC 61937 (used on S/PDIF - IEC958)"),
     .extensions        = "spdif",
     .priv_data_size    = sizeof(IEC61937Context),

     .audio_codec       = AV_CODEC_ID_AC3,
     .video_codec       = AV_CODEC_ID_NONE,

     .write_header      = spdif_write_header,
     .write_packet      = spdif_write_packet,
     .write_trailer     = spdif_write_trailer,

     .flags             = AVFMT_NOTIMESTAMPS,

     .priv_class        = &spdif_class,

 };