Subversion Repositories Kolibri OS

Rev

Blame | Last modification | View Log | RSS feed

  1. /*
  2.  * GXF demuxer.
  3.  * Copyright (c) 2006 Reimar Doeffinger
  4.  *
  5.  * This file is part of FFmpeg.
  6.  *
  7.  * FFmpeg is free software; you can redistribute it and/or
  8.  * modify it under the terms of the GNU Lesser General Public
  9.  * License as published by the Free Software Foundation; either
  10.  * version 2.1 of the License, or (at your option) any later version.
  11.  *
  12.  * FFmpeg is distributed in the hope that it will be useful,
  13.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15.  * Lesser General Public License for more details.
  16.  *
  17.  * You should have received a copy of the GNU Lesser General Public
  18.  * License along with FFmpeg; if not, write to the Free Software
  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20.  */
  21.  
  22. #include <inttypes.h>
  23.  
  24. #include "libavutil/channel_layout.h"
  25. #include "libavutil/common.h"
  26. #include "avformat.h"
  27. #include "internal.h"
  28. #include "gxf.h"
  29. #include "libavcodec/mpeg12data.h"
  30.  
  31. struct gxf_stream_info {
  32.     int64_t first_field;
  33.     int64_t last_field;
  34.     AVRational frames_per_second;
  35.     int32_t fields_per_frame;
  36.     int64_t track_aux_data;
  37. };
  38.  
  39. /**
  40.  * @brief parse gxf timecode and add it to metadata
  41.  */
  42. static int add_timecode_metadata(AVDictionary **pm, const char *key, uint32_t timecode, int fields_per_frame)
  43. {
  44.    char tmp[128];
  45.    int field  = timecode & 0xff;
  46.    int frame  = fields_per_frame ? field / fields_per_frame : field;
  47.    int second = (timecode >>  8) & 0xff;
  48.    int minute = (timecode >> 16) & 0xff;
  49.    int hour   = (timecode >> 24) & 0x1f;
  50.    int drop   = (timecode >> 29) & 1;
  51.    // bit 30: color_frame, unused
  52.    // ignore invalid time code
  53.    if (timecode >> 31)
  54.        return 0;
  55.    snprintf(tmp, sizeof(tmp), "%02d:%02d:%02d%c%02d",
  56.        hour, minute, second, drop ? ';' : ':', frame);
  57.    return av_dict_set(pm, key, tmp, 0);
  58. }
  59.  
  60. /**
  61.  * @brief parses a packet header, extracting type and length
  62.  * @param pb AVIOContext to read header from
  63.  * @param type detected packet type is stored here
  64.  * @param length detected packet length, excluding header is stored here
  65.  * @return 0 if header not found or contains invalid data, 1 otherwise
  66.  */
  67. static int parse_packet_header(AVIOContext *pb, GXFPktType *type, int *length) {
  68.     if (avio_rb32(pb))
  69.         return 0;
  70.     if (avio_r8(pb) != 1)
  71.         return 0;
  72.     *type = avio_r8(pb);
  73.     *length = avio_rb32(pb);
  74.     if ((*length >> 24) || *length < 16)
  75.         return 0;
  76.     *length -= 16;
  77.     if (avio_rb32(pb))
  78.         return 0;
  79.     if (avio_r8(pb) != 0xe1)
  80.         return 0;
  81.     if (avio_r8(pb) != 0xe2)
  82.         return 0;
  83.     return 1;
  84. }
  85.  
  86. /**
  87.  * @brief check if file starts with a PKT_MAP header
  88.  */
  89. static int gxf_probe(AVProbeData *p) {
  90.     static const uint8_t startcode[] = {0, 0, 0, 0, 1, 0xbc}; // start with map packet
  91.     static const uint8_t endcode[] = {0, 0, 0, 0, 0xe1, 0xe2};
  92.     if (!memcmp(p->buf, startcode, sizeof(startcode)) &&
  93.         !memcmp(&p->buf[16 - sizeof(endcode)], endcode, sizeof(endcode)))
  94.         return AVPROBE_SCORE_MAX;
  95.     return 0;
  96. }
  97.  
  98. /**
  99.  * @brief gets the stream index for the track with the specified id, creates new
  100.  *        stream if not found
  101.  * @param id     id of stream to find / add
  102.  * @param format stream format identifier
  103.  */
  104. static int get_sindex(AVFormatContext *s, int id, int format) {
  105.     int i;
  106.     AVStream *st = NULL;
  107.     i = ff_find_stream_index(s, id);
  108.     if (i >= 0)
  109.         return i;
  110.     st = avformat_new_stream(s, NULL);
  111.     if (!st)
  112.         return AVERROR(ENOMEM);
  113.     st->id = id;
  114.     switch (format) {
  115.         case 3:
  116.         case 4:
  117.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  118.             st->codec->codec_id = AV_CODEC_ID_MJPEG;
  119.             break;
  120.         case 13:
  121.         case 14:
  122.         case 15:
  123.         case 16:
  124.         case 25:
  125.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  126.             st->codec->codec_id = AV_CODEC_ID_DVVIDEO;
  127.             break;
  128.         case 11:
  129.         case 12:
  130.         case 20:
  131.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  132.             st->codec->codec_id = AV_CODEC_ID_MPEG2VIDEO;
  133.             st->need_parsing = AVSTREAM_PARSE_HEADERS; //get keyframe flag etc.
  134.             break;
  135.         case 22:
  136.         case 23:
  137.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  138.             st->codec->codec_id = AV_CODEC_ID_MPEG1VIDEO;
  139.             st->need_parsing = AVSTREAM_PARSE_HEADERS; //get keyframe flag etc.
  140.             break;
  141.         case 9:
  142.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  143.             st->codec->codec_id = AV_CODEC_ID_PCM_S24LE;
  144.             st->codec->channels = 1;
  145.             st->codec->channel_layout = AV_CH_LAYOUT_MONO;
  146.             st->codec->sample_rate = 48000;
  147.             st->codec->bit_rate = 3 * 1 * 48000 * 8;
  148.             st->codec->block_align = 3 * 1;
  149.             st->codec->bits_per_coded_sample = 24;
  150.             break;
  151.         case 10:
  152.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  153.             st->codec->codec_id = AV_CODEC_ID_PCM_S16LE;
  154.             st->codec->channels = 1;
  155.             st->codec->channel_layout = AV_CH_LAYOUT_MONO;
  156.             st->codec->sample_rate = 48000;
  157.             st->codec->bit_rate = 2 * 1 * 48000 * 8;
  158.             st->codec->block_align = 2 * 1;
  159.             st->codec->bits_per_coded_sample = 16;
  160.             break;
  161.         case 17:
  162.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  163.             st->codec->codec_id = AV_CODEC_ID_AC3;
  164.             st->codec->channels = 2;
  165.             st->codec->channel_layout = AV_CH_LAYOUT_STEREO;
  166.             st->codec->sample_rate = 48000;
  167.             break;
  168.         case 26: /* AVCi50 / AVCi100 (AVC Intra) */
  169.         case 29: /* AVCHD */
  170.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  171.             st->codec->codec_id = AV_CODEC_ID_H264;
  172.             st->need_parsing = AVSTREAM_PARSE_HEADERS;
  173.             break;
  174.         // timecode tracks:
  175.         case 7:
  176.         case 8:
  177.         case 24:
  178.             st->codec->codec_type = AVMEDIA_TYPE_DATA;
  179.             st->codec->codec_id = AV_CODEC_ID_NONE;
  180.             break;
  181.         case 30:
  182.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  183.             st->codec->codec_id = AV_CODEC_ID_DNXHD;
  184.             break;
  185.         default:
  186.             st->codec->codec_type = AVMEDIA_TYPE_UNKNOWN;
  187.             st->codec->codec_id = AV_CODEC_ID_NONE;
  188.             break;
  189.     }
  190.     return s->nb_streams - 1;
  191. }
  192.  
  193. /**
  194.  * @brief filters out interesting tags from material information.
  195.  * @param len length of tag section, will be adjusted to contain remaining bytes
  196.  * @param si struct to store collected information into
  197.  */
  198. static void gxf_material_tags(AVIOContext *pb, int *len, struct gxf_stream_info *si) {
  199.     si->first_field = AV_NOPTS_VALUE;
  200.     si->last_field = AV_NOPTS_VALUE;
  201.     while (*len >= 2) {
  202.         GXFMatTag tag = avio_r8(pb);
  203.         int tlen = avio_r8(pb);
  204.         *len -= 2;
  205.         if (tlen > *len)
  206.             return;
  207.         *len -= tlen;
  208.         if (tlen == 4) {
  209.             uint32_t value = avio_rb32(pb);
  210.             if (tag == MAT_FIRST_FIELD)
  211.                 si->first_field = value;
  212.             else if (tag == MAT_LAST_FIELD)
  213.                 si->last_field = value;
  214.         } else
  215.             avio_skip(pb, tlen);
  216.     }
  217. }
  218.  
  219. static const AVRational frame_rate_tab[] = {
  220.     {   60,    1},
  221.     {60000, 1001},
  222.     {   50,    1},
  223.     {   30,    1},
  224.     {30000, 1001},
  225.     {   25,    1},
  226.     {   24,    1},
  227.     {24000, 1001},
  228.     {    0,    0},
  229. };
  230.  
  231. /**
  232.  * @brief convert fps tag value to AVRational fps
  233.  * @param fps fps value from tag
  234.  * @return fps as AVRational, or 0 / 0 if unknown
  235.  */
  236. static AVRational fps_tag2avr(int32_t fps) {
  237.     if (fps < 1 || fps > 9) fps = 9;
  238.     return frame_rate_tab[fps - 1];
  239. }
  240.  
  241. /**
  242.  * @brief convert UMF attributes flags to AVRational fps
  243.  * @param flags UMF flags to convert
  244.  * @return fps as AVRational, or 0 / 0 if unknown
  245.  */
  246. static AVRational fps_umf2avr(uint32_t flags) {
  247.     static const AVRational map[] = {{50, 1}, {60000, 1001}, {24, 1},
  248.         {25, 1}, {30000, 1001}};
  249.     int idx =  av_log2((flags & 0x7c0) >> 6);
  250.     return map[idx];
  251. }
  252.  
  253. /**
  254.  * @brief filters out interesting tags from track information.
  255.  * @param len length of tag section, will be adjusted to contain remaining bytes
  256.  * @param si struct to store collected information into
  257.  */
  258. static void gxf_track_tags(AVIOContext *pb, int *len, struct gxf_stream_info *si) {
  259.     si->frames_per_second = (AVRational){0, 0};
  260.     si->fields_per_frame = 0;
  261.     si->track_aux_data = 0x80000000;
  262.     while (*len >= 2) {
  263.         GXFTrackTag tag = avio_r8(pb);
  264.         int tlen = avio_r8(pb);
  265.         *len -= 2;
  266.         if (tlen > *len)
  267.             return;
  268.         *len -= tlen;
  269.         if (tlen == 4) {
  270.             uint32_t value = avio_rb32(pb);
  271.             if (tag == TRACK_FPS)
  272.                 si->frames_per_second = fps_tag2avr(value);
  273.             else if (tag == TRACK_FPF && (value == 1 || value == 2))
  274.                 si->fields_per_frame = value;
  275.         } else if (tlen == 8 && tag == TRACK_AUX)
  276.             si->track_aux_data = avio_rl64(pb);
  277.         else
  278.             avio_skip(pb, tlen);
  279.     }
  280. }
  281.  
  282. /**
  283.  * @brief read index from FLT packet into stream 0 av_index
  284.  */
  285. static void gxf_read_index(AVFormatContext *s, int pkt_len) {
  286.     AVIOContext *pb = s->pb;
  287.     AVStream *st;
  288.     uint32_t fields_per_map = avio_rl32(pb);
  289.     uint32_t map_cnt = avio_rl32(pb);
  290.     int i;
  291.     pkt_len -= 8;
  292.     if ((s->flags & AVFMT_FLAG_IGNIDX) || !s->streams) {
  293.         avio_skip(pb, pkt_len);
  294.         return;
  295.     }
  296.     st = s->streams[0];
  297.     if (map_cnt > 1000) {
  298.         av_log(s, AV_LOG_ERROR,
  299.                "too many index entries %"PRIu32" (%"PRIx32")\n",
  300.                map_cnt, map_cnt);
  301.         map_cnt = 1000;
  302.     }
  303.     if (pkt_len < 4 * map_cnt) {
  304.         av_log(s, AV_LOG_ERROR, "invalid index length\n");
  305.         avio_skip(pb, pkt_len);
  306.         return;
  307.     }
  308.     pkt_len -= 4 * map_cnt;
  309.     av_add_index_entry(st, 0, 0, 0, 0, 0);
  310.     for (i = 0; i < map_cnt; i++)
  311.         av_add_index_entry(st, (uint64_t)avio_rl32(pb) * 1024,
  312.                            i * (uint64_t)fields_per_map + 1, 0, 0, 0);
  313.     avio_skip(pb, pkt_len);
  314. }
  315.  
  316. static int gxf_header(AVFormatContext *s) {
  317.     AVIOContext *pb = s->pb;
  318.     GXFPktType pkt_type;
  319.     int map_len;
  320.     int len;
  321.     AVRational main_timebase = {0, 0};
  322.     struct gxf_stream_info *si = s->priv_data;
  323.     int i;
  324.     if (!parse_packet_header(pb, &pkt_type, &map_len) || pkt_type != PKT_MAP) {
  325.         av_log(s, AV_LOG_ERROR, "map packet not found\n");
  326.         return 0;
  327.     }
  328.     map_len -= 2;
  329.     if (avio_r8(pb) != 0x0e0 || avio_r8(pb) != 0xff) {
  330.         av_log(s, AV_LOG_ERROR, "unknown version or invalid map preamble\n");
  331.         return 0;
  332.     }
  333.     map_len -= 2;
  334.     len = avio_rb16(pb); // length of material data section
  335.     if (len > map_len) {
  336.         av_log(s, AV_LOG_ERROR, "material data longer than map data\n");
  337.         return 0;
  338.     }
  339.     map_len -= len;
  340.     gxf_material_tags(pb, &len, si);
  341.     avio_skip(pb, len);
  342.     map_len -= 2;
  343.     len = avio_rb16(pb); // length of track description
  344.     if (len > map_len) {
  345.         av_log(s, AV_LOG_ERROR, "track description longer than map data\n");
  346.         return 0;
  347.     }
  348.     map_len -= len;
  349.     while (len > 0) {
  350.         int track_type, track_id, track_len;
  351.         AVStream *st;
  352.         int idx;
  353.         len -= 4;
  354.         track_type = avio_r8(pb);
  355.         track_id = avio_r8(pb);
  356.         track_len = avio_rb16(pb);
  357.         len -= track_len;
  358.         if (!(track_type & 0x80)) {
  359.            av_log(s, AV_LOG_ERROR, "invalid track type %x\n", track_type);
  360.            continue;
  361.         }
  362.         track_type &= 0x7f;
  363.         if ((track_id & 0xc0) != 0xc0) {
  364.            av_log(s, AV_LOG_ERROR, "invalid track id %x\n", track_id);
  365.            continue;
  366.         }
  367.         track_id &= 0x3f;
  368.         gxf_track_tags(pb, &track_len, si);
  369.         // check for timecode tracks
  370.         if (track_type == 7 || track_type == 8 || track_type == 24) {
  371.             add_timecode_metadata(&s->metadata, "timecode",
  372.                                   si->track_aux_data & 0xffffffff,
  373.                                   si->fields_per_frame);
  374.  
  375.         }
  376.         avio_skip(pb, track_len);
  377.  
  378.         idx = get_sindex(s, track_id, track_type);
  379.         if (idx < 0) continue;
  380.         st = s->streams[idx];
  381.         if (!main_timebase.num || !main_timebase.den) {
  382.             main_timebase.num = si->frames_per_second.den;
  383.             main_timebase.den = si->frames_per_second.num * 2;
  384.         }
  385.         st->start_time = si->first_field;
  386.         if (si->first_field != AV_NOPTS_VALUE && si->last_field != AV_NOPTS_VALUE)
  387.             st->duration = si->last_field - si->first_field;
  388.     }
  389.     if (len < 0)
  390.         av_log(s, AV_LOG_ERROR, "invalid track description length specified\n");
  391.     if (map_len)
  392.         avio_skip(pb, map_len);
  393.     if (!parse_packet_header(pb, &pkt_type, &len)) {
  394.         av_log(s, AV_LOG_ERROR, "sync lost in header\n");
  395.         return -1;
  396.     }
  397.     if (pkt_type == PKT_FLT) {
  398.         gxf_read_index(s, len);
  399.         if (!parse_packet_header(pb, &pkt_type, &len)) {
  400.             av_log(s, AV_LOG_ERROR, "sync lost in header\n");
  401.             return -1;
  402.         }
  403.     }
  404.     if (pkt_type == PKT_UMF) {
  405.         if (len >= 0x39) {
  406.             AVRational fps;
  407.             len -= 0x39;
  408.             avio_skip(pb, 5); // preamble
  409.             avio_skip(pb, 0x30); // payload description
  410.             fps = fps_umf2avr(avio_rl32(pb));
  411.             if (!main_timebase.num || !main_timebase.den) {
  412.                 av_log(s, AV_LOG_WARNING, "No FPS track tag, using UMF fps tag."
  413.                                           " This might give wrong results.\n");
  414.                 // this may not always be correct, but simply the best we can get
  415.                 main_timebase.num = fps.den;
  416.                 main_timebase.den = fps.num * 2;
  417.             }
  418.  
  419.             if (len >= 0x18) {
  420.                 len -= 0x18;
  421.                 avio_skip(pb, 0x10);
  422.                 add_timecode_metadata(&s->metadata, "timecode_at_mark_in",
  423.                                       avio_rl32(pb), si->fields_per_frame);
  424.                 add_timecode_metadata(&s->metadata, "timecode_at_mark_out",
  425.                                       avio_rl32(pb), si->fields_per_frame);
  426.             }
  427.         } else
  428.             av_log(s, AV_LOG_INFO, "UMF packet too short\n");
  429.     } else
  430.         av_log(s, AV_LOG_INFO, "UMF packet missing\n");
  431.     avio_skip(pb, len);
  432.     // set a fallback value, 60000/1001 is specified for audio-only files
  433.     // so use that regardless of why we do not know the video frame rate.
  434.     if (!main_timebase.num || !main_timebase.den)
  435.         main_timebase = (AVRational){1001, 60000};
  436.     for (i = 0; i < s->nb_streams; i++) {
  437.         AVStream *st = s->streams[i];
  438.         avpriv_set_pts_info(st, 32, main_timebase.num, main_timebase.den);
  439.     }
  440.     return 0;
  441. }
  442.  
  443. #define READ_ONE() \
  444.     { \
  445.         if (!max_interval-- || avio_feof(pb)) \
  446.             goto out; \
  447.         tmp = tmp << 8 | avio_r8(pb); \
  448.     }
  449.  
  450. /**
  451.  * @brief resync the stream on the next media packet with specified properties
  452.  * @param max_interval how many bytes to search for matching packet at most
  453.  * @param track track id the media packet must belong to, -1 for any
  454.  * @param timestamp minimum timestamp (== field number) the packet must have, -1 for any
  455.  * @return timestamp of packet found
  456.  */
  457. static int64_t gxf_resync_media(AVFormatContext *s, uint64_t max_interval, int track, int timestamp) {
  458.     uint32_t tmp;
  459.     uint64_t last_pos;
  460.     uint64_t last_found_pos = 0;
  461.     int cur_track;
  462.     int64_t cur_timestamp = AV_NOPTS_VALUE;
  463.     int len;
  464.     AVIOContext *pb = s->pb;
  465.     GXFPktType type;
  466.     tmp = avio_rb32(pb);
  467. start:
  468.     while (tmp)
  469.         READ_ONE();
  470.     READ_ONE();
  471.     if (tmp != 1)
  472.         goto start;
  473.     last_pos = avio_tell(pb);
  474.     if (avio_seek(pb, -5, SEEK_CUR) < 0)
  475.         goto out;
  476.     if (!parse_packet_header(pb, &type, &len) || type != PKT_MEDIA) {
  477.         if (avio_seek(pb, last_pos, SEEK_SET) < 0)
  478.             goto out;
  479.         goto start;
  480.     }
  481.     avio_r8(pb);
  482.     cur_track = avio_r8(pb);
  483.     cur_timestamp = avio_rb32(pb);
  484.     last_found_pos = avio_tell(pb) - 16 - 6;
  485.     if ((track >= 0 && track != cur_track) || (timestamp >= 0 && timestamp > cur_timestamp)) {
  486.         if (avio_seek(pb, last_pos, SEEK_SET) >= 0)
  487.             goto start;
  488.     }
  489. out:
  490.     if (last_found_pos)
  491.         avio_seek(pb, last_found_pos, SEEK_SET);
  492.     return cur_timestamp;
  493. }
  494.  
  495. static int gxf_packet(AVFormatContext *s, AVPacket *pkt) {
  496.     AVIOContext *pb = s->pb;
  497.     GXFPktType pkt_type;
  498.     int pkt_len;
  499.     struct gxf_stream_info *si = s->priv_data;
  500.  
  501.     while (!pb->eof_reached) {
  502.         AVStream *st;
  503.         int track_type, track_id, ret;
  504.         int field_nr, field_info, skip = 0;
  505.         int stream_index;
  506.         if (!parse_packet_header(pb, &pkt_type, &pkt_len)) {
  507.             if (!avio_feof(pb))
  508.                 av_log(s, AV_LOG_ERROR, "sync lost\n");
  509.             return -1;
  510.         }
  511.         if (pkt_type == PKT_FLT) {
  512.             gxf_read_index(s, pkt_len);
  513.             continue;
  514.         }
  515.         if (pkt_type != PKT_MEDIA) {
  516.             avio_skip(pb, pkt_len);
  517.             continue;
  518.         }
  519.         if (pkt_len < 16) {
  520.             av_log(s, AV_LOG_ERROR, "invalid media packet length\n");
  521.             continue;
  522.         }
  523.         pkt_len -= 16;
  524.         track_type = avio_r8(pb);
  525.         track_id = avio_r8(pb);
  526.         stream_index = get_sindex(s, track_id, track_type);
  527.         if (stream_index < 0)
  528.             return stream_index;
  529.         st = s->streams[stream_index];
  530.         field_nr = avio_rb32(pb);
  531.         field_info = avio_rb32(pb);
  532.         avio_rb32(pb); // "timeline" field number
  533.         avio_r8(pb); // flags
  534.         avio_r8(pb); // reserved
  535.         if (st->codec->codec_id == AV_CODEC_ID_PCM_S24LE ||
  536.             st->codec->codec_id == AV_CODEC_ID_PCM_S16LE) {
  537.             int first = field_info >> 16;
  538.             int last  = field_info & 0xffff; // last is exclusive
  539.             int bps = av_get_bits_per_sample(st->codec->codec_id)>>3;
  540.             if (first <= last && last*bps <= pkt_len) {
  541.                 avio_skip(pb, first*bps);
  542.                 skip = pkt_len - last*bps;
  543.                 pkt_len = (last-first)*bps;
  544.             } else
  545.                 av_log(s, AV_LOG_ERROR, "invalid first and last sample values\n");
  546.         }
  547.         ret = av_get_packet(pb, pkt, pkt_len);
  548.         if (skip)
  549.             avio_skip(pb, skip);
  550.         pkt->stream_index = stream_index;
  551.         pkt->dts = field_nr;
  552.  
  553.         //set duration manually for DV or else lavf misdetects the frame rate
  554.         if (st->codec->codec_id == AV_CODEC_ID_DVVIDEO)
  555.             pkt->duration = si->fields_per_frame;
  556.  
  557.         return ret;
  558.     }
  559.     return AVERROR_EOF;
  560. }
  561.  
  562. static int gxf_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags) {
  563.     int64_t res = 0;
  564.     uint64_t pos;
  565.     uint64_t maxlen = 100 * 1024 * 1024;
  566.     AVStream *st = s->streams[0];
  567.     int64_t start_time = s->streams[stream_index]->start_time;
  568.     int64_t found;
  569.     int idx;
  570.     if (timestamp < start_time) timestamp = start_time;
  571.     idx = av_index_search_timestamp(st, timestamp - start_time,
  572.                                     AVSEEK_FLAG_ANY | AVSEEK_FLAG_BACKWARD);
  573.     if (idx < 0)
  574.         return -1;
  575.     pos = st->index_entries[idx].pos;
  576.     if (idx < st->nb_index_entries - 2)
  577.         maxlen = st->index_entries[idx + 2].pos - pos;
  578.     maxlen = FFMAX(maxlen, 200 * 1024);
  579.     res = avio_seek(s->pb, pos, SEEK_SET);
  580.     if (res < 0)
  581.         return res;
  582.     found = gxf_resync_media(s, maxlen, -1, timestamp);
  583.     if (FFABS(found - timestamp) > 4)
  584.         return -1;
  585.     return 0;
  586. }
  587.  
  588. static int64_t gxf_read_timestamp(AVFormatContext *s, int stream_index,
  589.                                   int64_t *pos, int64_t pos_limit) {
  590.     AVIOContext *pb = s->pb;
  591.     int64_t res;
  592.     if (avio_seek(pb, *pos, SEEK_SET) < 0)
  593.         return AV_NOPTS_VALUE;
  594.     res = gxf_resync_media(s, pos_limit - *pos, -1, -1);
  595.     *pos = avio_tell(pb);
  596.     return res;
  597. }
  598.  
  599. AVInputFormat ff_gxf_demuxer = {
  600.     .name           = "gxf",
  601.     .long_name      = NULL_IF_CONFIG_SMALL("GXF (General eXchange Format)"),
  602.     .priv_data_size = sizeof(struct gxf_stream_info),
  603.     .read_probe     = gxf_probe,
  604.     .read_header    = gxf_header,
  605.     .read_packet    = gxf_packet,
  606.     .read_seek      = gxf_seek,
  607.     .read_timestamp = gxf_read_timestamp,
  608. };
  609.