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 "libavutil/channel_layout.h"
  23. #include "libavutil/common.h"
  24. #include "avformat.h"
  25. #include "internal.h"
  26. #include "gxf.h"
  27. #include "libavcodec/mpeg12data.h"
  28.  
  29. struct gxf_stream_info {
  30.     int64_t first_field;
  31.     int64_t last_field;
  32.     AVRational frames_per_second;
  33.     int32_t fields_per_frame;
  34.     int64_t track_aux_data;
  35. };
  36.  
  37. /**
  38.  * @brief parse gxf timecode and add it to metadata
  39.  */
  40. static int add_timecode_metadata(AVDictionary **pm, const char *key, uint32_t timecode, int fields_per_frame)
  41. {
  42.    char tmp[128];
  43.    int field  = timecode & 0xff;
  44.    int frame  = fields_per_frame ? field / fields_per_frame : field;
  45.    int second = (timecode >>  8) & 0xff;
  46.    int minute = (timecode >> 16) & 0xff;
  47.    int hour   = (timecode >> 24) & 0x1f;
  48.    int drop   = (timecode >> 29) & 1;
  49.    // bit 30: color_frame, unused
  50.    // ignore invalid time code
  51.    if (timecode >> 31)
  52.        return 0;
  53.    snprintf(tmp, sizeof(tmp), "%02d:%02d:%02d%c%02d",
  54.        hour, minute, second, drop ? ';' : ':', frame);
  55.    return av_dict_set(pm, key, tmp, 0);
  56. }
  57.  
  58. /**
  59.  * @brief parses a packet header, extracting type and length
  60.  * @param pb AVIOContext to read header from
  61.  * @param type detected packet type is stored here
  62.  * @param length detected packet length, excluding header is stored here
  63.  * @return 0 if header not found or contains invalid data, 1 otherwise
  64.  */
  65. static int parse_packet_header(AVIOContext *pb, GXFPktType *type, int *length) {
  66.     if (avio_rb32(pb))
  67.         return 0;
  68.     if (avio_r8(pb) != 1)
  69.         return 0;
  70.     *type = avio_r8(pb);
  71.     *length = avio_rb32(pb);
  72.     if ((*length >> 24) || *length < 16)
  73.         return 0;
  74.     *length -= 16;
  75.     if (avio_rb32(pb))
  76.         return 0;
  77.     if (avio_r8(pb) != 0xe1)
  78.         return 0;
  79.     if (avio_r8(pb) != 0xe2)
  80.         return 0;
  81.     return 1;
  82. }
  83.  
  84. /**
  85.  * @brief check if file starts with a PKT_MAP header
  86.  */
  87. static int gxf_probe(AVProbeData *p) {
  88.     static const uint8_t startcode[] = {0, 0, 0, 0, 1, 0xbc}; // start with map packet
  89.     static const uint8_t endcode[] = {0, 0, 0, 0, 0xe1, 0xe2};
  90.     if (!memcmp(p->buf, startcode, sizeof(startcode)) &&
  91.         !memcmp(&p->buf[16 - sizeof(endcode)], endcode, sizeof(endcode)))
  92.         return AVPROBE_SCORE_MAX;
  93.     return 0;
  94. }
  95.  
  96. /**
  97.  * @brief gets the stream index for the track with the specified id, creates new
  98.  *        stream if not found
  99.  * @param id     id of stream to find / add
  100.  * @param format stream format identifier
  101.  */
  102. static int get_sindex(AVFormatContext *s, int id, int format) {
  103.     int i;
  104.     AVStream *st = NULL;
  105.     i = ff_find_stream_index(s, id);
  106.     if (i >= 0)
  107.         return i;
  108.     st = avformat_new_stream(s, NULL);
  109.     if (!st)
  110.         return AVERROR(ENOMEM);
  111.     st->id = id;
  112.     switch (format) {
  113.         case 3:
  114.         case 4:
  115.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  116.             st->codec->codec_id = AV_CODEC_ID_MJPEG;
  117.             break;
  118.         case 13:
  119.         case 14:
  120.         case 15:
  121.         case 16:
  122.         case 25:
  123.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  124.             st->codec->codec_id = AV_CODEC_ID_DVVIDEO;
  125.             break;
  126.         case 11:
  127.         case 12:
  128.         case 20:
  129.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  130.             st->codec->codec_id = AV_CODEC_ID_MPEG2VIDEO;
  131.             st->need_parsing = AVSTREAM_PARSE_HEADERS; //get keyframe flag etc.
  132.             break;
  133.         case 22:
  134.         case 23:
  135.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  136.             st->codec->codec_id = AV_CODEC_ID_MPEG1VIDEO;
  137.             st->need_parsing = AVSTREAM_PARSE_HEADERS; //get keyframe flag etc.
  138.             break;
  139.         case 9:
  140.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  141.             st->codec->codec_id = AV_CODEC_ID_PCM_S24LE;
  142.             st->codec->channels = 1;
  143.             st->codec->channel_layout = AV_CH_LAYOUT_MONO;
  144.             st->codec->sample_rate = 48000;
  145.             st->codec->bit_rate = 3 * 1 * 48000 * 8;
  146.             st->codec->block_align = 3 * 1;
  147.             st->codec->bits_per_coded_sample = 24;
  148.             break;
  149.         case 10:
  150.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  151.             st->codec->codec_id = AV_CODEC_ID_PCM_S16LE;
  152.             st->codec->channels = 1;
  153.             st->codec->channel_layout = AV_CH_LAYOUT_MONO;
  154.             st->codec->sample_rate = 48000;
  155.             st->codec->bit_rate = 2 * 1 * 48000 * 8;
  156.             st->codec->block_align = 2 * 1;
  157.             st->codec->bits_per_coded_sample = 16;
  158.             break;
  159.         case 17:
  160.             st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  161.             st->codec->codec_id = AV_CODEC_ID_AC3;
  162.             st->codec->channels = 2;
  163.             st->codec->channel_layout = AV_CH_LAYOUT_STEREO;
  164.             st->codec->sample_rate = 48000;
  165.             break;
  166.         case 26: /* AVCi50 / AVCi100 (AVC Intra) */
  167.         case 29: /* AVCHD */
  168.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  169.             st->codec->codec_id = CODEC_ID_H264;
  170.             st->need_parsing = AVSTREAM_PARSE_HEADERS;
  171.             break;
  172.         // timecode tracks:
  173.         case 7:
  174.         case 8:
  175.         case 24:
  176.             st->codec->codec_type = AVMEDIA_TYPE_DATA;
  177.             st->codec->codec_id = AV_CODEC_ID_NONE;
  178.             break;
  179.         case 30:
  180.             st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
  181.             st->codec->codec_id = AV_CODEC_ID_DNXHD;
  182.             break;
  183.         default:
  184.             st->codec->codec_type = AVMEDIA_TYPE_UNKNOWN;
  185.             st->codec->codec_id = AV_CODEC_ID_NONE;
  186.             break;
  187.     }
  188.     return s->nb_streams - 1;
  189. }
  190.  
  191. /**
  192.  * @brief filters out interesting tags from material information.
  193.  * @param len length of tag section, will be adjusted to contain remaining bytes
  194.  * @param si struct to store collected information into
  195.  */
  196. static void gxf_material_tags(AVIOContext *pb, int *len, struct gxf_stream_info *si) {
  197.     si->first_field = AV_NOPTS_VALUE;
  198.     si->last_field = AV_NOPTS_VALUE;
  199.     while (*len >= 2) {
  200.         GXFMatTag tag = avio_r8(pb);
  201.         int tlen = avio_r8(pb);
  202.         *len -= 2;
  203.         if (tlen > *len)
  204.             return;
  205.         *len -= tlen;
  206.         if (tlen == 4) {
  207.             uint32_t value = avio_rb32(pb);
  208.             if (tag == MAT_FIRST_FIELD)
  209.                 si->first_field = value;
  210.             else if (tag == MAT_LAST_FIELD)
  211.                 si->last_field = value;
  212.         } else
  213.             avio_skip(pb, tlen);
  214.     }
  215. }
  216.  
  217. static const AVRational frame_rate_tab[] = {
  218.     {   60,    1},
  219.     {60000, 1001},
  220.     {   50,    1},
  221.     {   30,    1},
  222.     {30000, 1001},
  223.     {   25,    1},
  224.     {   24,    1},
  225.     {24000, 1001},
  226.     {    0,    0},
  227. };
  228.  
  229. /**
  230.  * @brief convert fps tag value to AVRational fps
  231.  * @param fps fps value from tag
  232.  * @return fps as AVRational, or 0 / 0 if unknown
  233.  */
  234. static AVRational fps_tag2avr(int32_t fps) {
  235.     if (fps < 1 || fps > 9) fps = 9;
  236.     return frame_rate_tab[fps - 1];
  237. }
  238.  
  239. /**
  240.  * @brief convert UMF attributes flags to AVRational fps
  241.  * @param flags UMF flags to convert
  242.  * @return fps as AVRational, or 0 / 0 if unknown
  243.  */
  244. static AVRational fps_umf2avr(uint32_t flags) {
  245.     static const AVRational map[] = {{50, 1}, {60000, 1001}, {24, 1},
  246.         {25, 1}, {30000, 1001}};
  247.     int idx =  av_log2((flags & 0x7c0) >> 6);
  248.     return map[idx];
  249. }
  250.  
  251. /**
  252.  * @brief filters out interesting tags from track information.
  253.  * @param len length of tag section, will be adjusted to contain remaining bytes
  254.  * @param si struct to store collected information into
  255.  */
  256. static void gxf_track_tags(AVIOContext *pb, int *len, struct gxf_stream_info *si) {
  257.     si->frames_per_second = (AVRational){0, 0};
  258.     si->fields_per_frame = 0;
  259.     si->track_aux_data = 0x80000000;
  260.     while (*len >= 2) {
  261.         GXFTrackTag tag = avio_r8(pb);
  262.         int tlen = avio_r8(pb);
  263.         *len -= 2;
  264.         if (tlen > *len)
  265.             return;
  266.         *len -= tlen;
  267.         if (tlen == 4) {
  268.             uint32_t value = avio_rb32(pb);
  269.             if (tag == TRACK_FPS)
  270.                 si->frames_per_second = fps_tag2avr(value);
  271.             else if (tag == TRACK_FPF && (value == 1 || value == 2))
  272.                 si->fields_per_frame = value;
  273.         } else if (tlen == 8 && tag == TRACK_AUX)
  274.             si->track_aux_data = avio_rl64(pb);
  275.         else
  276.             avio_skip(pb, tlen);
  277.     }
  278. }
  279.  
  280. /**
  281.  * @brief read index from FLT packet into stream 0 av_index
  282.  */
  283. static void gxf_read_index(AVFormatContext *s, int pkt_len) {
  284.     AVIOContext *pb = s->pb;
  285.     AVStream *st;
  286.     uint32_t fields_per_map = avio_rl32(pb);
  287.     uint32_t map_cnt = avio_rl32(pb);
  288.     int i;
  289.     pkt_len -= 8;
  290.     if ((s->flags & AVFMT_FLAG_IGNIDX) || !s->streams) {
  291.         avio_skip(pb, pkt_len);
  292.         return;
  293.     }
  294.     st = s->streams[0];
  295.     if (map_cnt > 1000) {
  296.         av_log(s, AV_LOG_ERROR, "too many index entries %u (%x)\n", map_cnt, map_cnt);
  297.         map_cnt = 1000;
  298.     }
  299.     if (pkt_len < 4 * map_cnt) {
  300.         av_log(s, AV_LOG_ERROR, "invalid index length\n");
  301.         avio_skip(pb, pkt_len);
  302.         return;
  303.     }
  304.     pkt_len -= 4 * map_cnt;
  305.     av_add_index_entry(st, 0, 0, 0, 0, 0);
  306.     for (i = 0; i < map_cnt; i++)
  307.         av_add_index_entry(st, (uint64_t)avio_rl32(pb) * 1024,
  308.                            i * (uint64_t)fields_per_map + 1, 0, 0, 0);
  309.     avio_skip(pb, pkt_len);
  310. }
  311.  
  312. static int gxf_header(AVFormatContext *s) {
  313.     AVIOContext *pb = s->pb;
  314.     GXFPktType pkt_type;
  315.     int map_len;
  316.     int len;
  317.     AVRational main_timebase = {0, 0};
  318.     struct gxf_stream_info *si = s->priv_data;
  319.     int i;
  320.     if (!parse_packet_header(pb, &pkt_type, &map_len) || pkt_type != PKT_MAP) {
  321.         av_log(s, AV_LOG_ERROR, "map packet not found\n");
  322.         return 0;
  323.     }
  324.     map_len -= 2;
  325.     if (avio_r8(pb) != 0x0e0 || avio_r8(pb) != 0xff) {
  326.         av_log(s, AV_LOG_ERROR, "unknown version or invalid map preamble\n");
  327.         return 0;
  328.     }
  329.     map_len -= 2;
  330.     len = avio_rb16(pb); // length of material data section
  331.     if (len > map_len) {
  332.         av_log(s, AV_LOG_ERROR, "material data longer than map data\n");
  333.         return 0;
  334.     }
  335.     map_len -= len;
  336.     gxf_material_tags(pb, &len, si);
  337.     avio_skip(pb, len);
  338.     map_len -= 2;
  339.     len = avio_rb16(pb); // length of track description
  340.     if (len > map_len) {
  341.         av_log(s, AV_LOG_ERROR, "track description longer than map data\n");
  342.         return 0;
  343.     }
  344.     map_len -= len;
  345.     while (len > 0) {
  346.         int track_type, track_id, track_len;
  347.         AVStream *st;
  348.         int idx;
  349.         len -= 4;
  350.         track_type = avio_r8(pb);
  351.         track_id = avio_r8(pb);
  352.         track_len = avio_rb16(pb);
  353.         len -= track_len;
  354.         if (!(track_type & 0x80)) {
  355.            av_log(s, AV_LOG_ERROR, "invalid track type %x\n", track_type);
  356.            continue;
  357.         }
  358.         track_type &= 0x7f;
  359.         if ((track_id & 0xc0) != 0xc0) {
  360.            av_log(s, AV_LOG_ERROR, "invalid track id %x\n", track_id);
  361.            continue;
  362.         }
  363.         track_id &= 0x3f;
  364.         gxf_track_tags(pb, &track_len, si);
  365.         // check for timecode tracks
  366.         if (track_type == 7 || track_type == 8 || track_type == 24) {
  367.             add_timecode_metadata(&s->metadata, "timecode",
  368.                                   si->track_aux_data & 0xffffffff,
  369.                                   si->fields_per_frame);
  370.  
  371.         }
  372.         avio_skip(pb, track_len);
  373.  
  374.         idx = get_sindex(s, track_id, track_type);
  375.         if (idx < 0) continue;
  376.         st = s->streams[idx];
  377.         if (!main_timebase.num || !main_timebase.den) {
  378.             main_timebase.num = si->frames_per_second.den;
  379.             main_timebase.den = si->frames_per_second.num * 2;
  380.         }
  381.         st->start_time = si->first_field;
  382.         if (si->first_field != AV_NOPTS_VALUE && si->last_field != AV_NOPTS_VALUE)
  383.             st->duration = si->last_field - si->first_field;
  384.     }
  385.     if (len < 0)
  386.         av_log(s, AV_LOG_ERROR, "invalid track description length specified\n");
  387.     if (map_len)
  388.         avio_skip(pb, map_len);
  389.     if (!parse_packet_header(pb, &pkt_type, &len)) {
  390.         av_log(s, AV_LOG_ERROR, "sync lost in header\n");
  391.         return -1;
  392.     }
  393.     if (pkt_type == PKT_FLT) {
  394.         gxf_read_index(s, len);
  395.         if (!parse_packet_header(pb, &pkt_type, &len)) {
  396.             av_log(s, AV_LOG_ERROR, "sync lost in header\n");
  397.             return -1;
  398.         }
  399.     }
  400.     if (pkt_type == PKT_UMF) {
  401.         if (len >= 0x39) {
  402.             AVRational fps;
  403.             len -= 0x39;
  404.             avio_skip(pb, 5); // preamble
  405.             avio_skip(pb, 0x30); // payload description
  406.             fps = fps_umf2avr(avio_rl32(pb));
  407.             if (!main_timebase.num || !main_timebase.den) {
  408.                 av_log(s, AV_LOG_WARNING, "No FPS track tag, using UMF fps tag."
  409.                                           " This might give wrong results.\n");
  410.                 // this may not always be correct, but simply the best we can get
  411.                 main_timebase.num = fps.den;
  412.                 main_timebase.den = fps.num * 2;
  413.             }
  414.  
  415.             if (len >= 0x18) {
  416.                 len -= 0x18;
  417.                 avio_skip(pb, 0x10);
  418.                 add_timecode_metadata(&s->metadata, "timecode_at_mark_in",
  419.                                       avio_rl32(pb), si->fields_per_frame);
  420.                 add_timecode_metadata(&s->metadata, "timecode_at_mark_out",
  421.                                       avio_rl32(pb), si->fields_per_frame);
  422.             }
  423.         } else
  424.             av_log(s, AV_LOG_INFO, "UMF packet too short\n");
  425.     } else
  426.         av_log(s, AV_LOG_INFO, "UMF packet missing\n");
  427.     avio_skip(pb, len);
  428.     // set a fallback value, 60000/1001 is specified for audio-only files
  429.     // so use that regardless of why we do not know the video frame rate.
  430.     if (!main_timebase.num || !main_timebase.den)
  431.         main_timebase = (AVRational){1001, 60000};
  432.     for (i = 0; i < s->nb_streams; i++) {
  433.         AVStream *st = s->streams[i];
  434.         avpriv_set_pts_info(st, 32, main_timebase.num, main_timebase.den);
  435.     }
  436.     return 0;
  437. }
  438.  
  439. #define READ_ONE() \
  440.     { \
  441.         if (!max_interval-- || url_feof(pb)) \
  442.             goto out; \
  443.         tmp = tmp << 8 | avio_r8(pb); \
  444.     }
  445.  
  446. /**
  447.  * @brief resync the stream on the next media packet with specified properties
  448.  * @param max_interval how many bytes to search for matching packet at most
  449.  * @param track track id the media packet must belong to, -1 for any
  450.  * @param timestamp minimum timestamp (== field number) the packet must have, -1 for any
  451.  * @return timestamp of packet found
  452.  */
  453. static int64_t gxf_resync_media(AVFormatContext *s, uint64_t max_interval, int track, int timestamp) {
  454.     uint32_t tmp;
  455.     uint64_t last_pos;
  456.     uint64_t last_found_pos = 0;
  457.     int cur_track;
  458.     int64_t cur_timestamp = AV_NOPTS_VALUE;
  459.     int len;
  460.     AVIOContext *pb = s->pb;
  461.     GXFPktType type;
  462.     tmp = avio_rb32(pb);
  463. start:
  464.     while (tmp)
  465.         READ_ONE();
  466.     READ_ONE();
  467.     if (tmp != 1)
  468.         goto start;
  469.     last_pos = avio_tell(pb);
  470.     if (avio_seek(pb, -5, SEEK_CUR) < 0)
  471.         goto out;
  472.     if (!parse_packet_header(pb, &type, &len) || type != PKT_MEDIA) {
  473.         if (avio_seek(pb, last_pos, SEEK_SET) < 0)
  474.             goto out;
  475.         goto start;
  476.     }
  477.     avio_r8(pb);
  478.     cur_track = avio_r8(pb);
  479.     cur_timestamp = avio_rb32(pb);
  480.     last_found_pos = avio_tell(pb) - 16 - 6;
  481.     if ((track >= 0 && track != cur_track) || (timestamp >= 0 && timestamp > cur_timestamp)) {
  482.         if (avio_seek(pb, last_pos, SEEK_SET) >= 0)
  483.             goto start;
  484.     }
  485. out:
  486.     if (last_found_pos)
  487.         avio_seek(pb, last_found_pos, SEEK_SET);
  488.     return cur_timestamp;
  489. }
  490.  
  491. static int gxf_packet(AVFormatContext *s, AVPacket *pkt) {
  492.     AVIOContext *pb = s->pb;
  493.     GXFPktType pkt_type;
  494.     int pkt_len;
  495.     struct gxf_stream_info *si = s->priv_data;
  496.  
  497.     while (!pb->eof_reached) {
  498.         AVStream *st;
  499.         int track_type, track_id, ret;
  500.         int field_nr, field_info, skip = 0;
  501.         int stream_index;
  502.         if (!parse_packet_header(pb, &pkt_type, &pkt_len)) {
  503.             if (!url_feof(pb))
  504.                 av_log(s, AV_LOG_ERROR, "sync lost\n");
  505.             return -1;
  506.         }
  507.         if (pkt_type == PKT_FLT) {
  508.             gxf_read_index(s, pkt_len);
  509.             continue;
  510.         }
  511.         if (pkt_type != PKT_MEDIA) {
  512.             avio_skip(pb, pkt_len);
  513.             continue;
  514.         }
  515.         if (pkt_len < 16) {
  516.             av_log(s, AV_LOG_ERROR, "invalid media packet length\n");
  517.             continue;
  518.         }
  519.         pkt_len -= 16;
  520.         track_type = avio_r8(pb);
  521.         track_id = avio_r8(pb);
  522.         stream_index = get_sindex(s, track_id, track_type);
  523.         if (stream_index < 0)
  524.             return stream_index;
  525.         st = s->streams[stream_index];
  526.         field_nr = avio_rb32(pb);
  527.         field_info = avio_rb32(pb);
  528.         avio_rb32(pb); // "timeline" field number
  529.         avio_r8(pb); // flags
  530.         avio_r8(pb); // reserved
  531.         if (st->codec->codec_id == AV_CODEC_ID_PCM_S24LE ||
  532.             st->codec->codec_id == AV_CODEC_ID_PCM_S16LE) {
  533.             int first = field_info >> 16;
  534.             int last  = field_info & 0xffff; // last is exclusive
  535.             int bps = av_get_bits_per_sample(st->codec->codec_id)>>3;
  536.             if (first <= last && last*bps <= pkt_len) {
  537.                 avio_skip(pb, first*bps);
  538.                 skip = pkt_len - last*bps;
  539.                 pkt_len = (last-first)*bps;
  540.             } else
  541.                 av_log(s, AV_LOG_ERROR, "invalid first and last sample values\n");
  542.         }
  543.         ret = av_get_packet(pb, pkt, pkt_len);
  544.         if (skip)
  545.             avio_skip(pb, skip);
  546.         pkt->stream_index = stream_index;
  547.         pkt->dts = field_nr;
  548.  
  549.         //set duration manually for DV or else lavf misdetects the frame rate
  550.         if (st->codec->codec_id == AV_CODEC_ID_DVVIDEO)
  551.             pkt->duration = si->fields_per_frame;
  552.  
  553.         return ret;
  554.     }
  555.     return AVERROR_EOF;
  556. }
  557.  
  558. static int gxf_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags) {
  559.     int res = 0;
  560.     uint64_t pos;
  561.     uint64_t maxlen = 100 * 1024 * 1024;
  562.     AVStream *st = s->streams[0];
  563.     int64_t start_time = s->streams[stream_index]->start_time;
  564.     int64_t found;
  565.     int idx;
  566.     if (timestamp < start_time) timestamp = start_time;
  567.     idx = av_index_search_timestamp(st, timestamp - start_time,
  568.                                     AVSEEK_FLAG_ANY | AVSEEK_FLAG_BACKWARD);
  569.     if (idx < 0)
  570.         return -1;
  571.     pos = st->index_entries[idx].pos;
  572.     if (idx < st->nb_index_entries - 2)
  573.         maxlen = st->index_entries[idx + 2].pos - pos;
  574.     maxlen = FFMAX(maxlen, 200 * 1024);
  575.     res = avio_seek(s->pb, pos, SEEK_SET);
  576.     if (res < 0)
  577.         return res;
  578.     found = gxf_resync_media(s, maxlen, -1, timestamp);
  579.     if (FFABS(found - timestamp) > 4)
  580.         return -1;
  581.     return 0;
  582. }
  583.  
  584. static int64_t gxf_read_timestamp(AVFormatContext *s, int stream_index,
  585.                                   int64_t *pos, int64_t pos_limit) {
  586.     AVIOContext *pb = s->pb;
  587.     int64_t res;
  588.     if (avio_seek(pb, *pos, SEEK_SET) < 0)
  589.         return AV_NOPTS_VALUE;
  590.     res = gxf_resync_media(s, pos_limit - *pos, -1, -1);
  591.     *pos = avio_tell(pb);
  592.     return res;
  593. }
  594.  
  595. AVInputFormat ff_gxf_demuxer = {
  596.     .name           = "gxf",
  597.     .long_name      = NULL_IF_CONFIG_SMALL("GXF (General eXchange Format)"),
  598.     .priv_data_size = sizeof(struct gxf_stream_info),
  599.     .read_probe     = gxf_probe,
  600.     .read_header    = gxf_header,
  601.     .read_packet    = gxf_packet,
  602.     .read_seek      = gxf_seek,
  603.     .read_timestamp = gxf_read_timestamp,
  604. };
  605.