FFmpeg SDK Use instance output_example analysis of the second

Four, the main function code
001 int Main (int argc, char **argv)
002 {
003 const char *filename;
004 Avoutputformat *FMT;
005 Avformatcontext *oc;
006 Avstream *audio_st, *video_st;
007 double audio_pts, video_pts;
008 int i;

/* Initialize LIBAVCODEC, and register all codecs and formats */
009 Av_register_all ();

010 if (argc! = 2) {
011 printf ("Usage:%s output_file\n")
"API example program to output a media file with libavformat.\n"
"The output format is automatically guessed according to the file extension.\n"
"Raw images can also is output by using '%%d ' in the filename\n"
"\ n", argv[0]);
012 exit (1);
}

013 filename = argv[1];

/* Auto detect the output format from the name. Default is MPEG. */
014 FMT = Guess_format (null, filename, null);
015 if (!FMT) {
016 printf ("Could not deduce output format from file extension:using mpeg.\n");
017 FMT = Guess_format ("MPEG", NULL, NULL);
018}
019 if (!FMT) {
fprintf (stderr, "Could not find suitable output format\n");
Exit (1);
}


/* Allocate the output media context */
020 oc = Avformat_alloc_context ();
021 if (!OC) {
022 fprintf (stderr, "Memory error\n");
023 exit (1);
024}
025 Oc->oformat = FMT;
026 snprintf (oc->filename, sizeof (Oc->filename), "%s", filename);

/* Add the audio and video streams using the default format codecs
and initialize the codecs * *
027 Video_st = NULL;
028 Audio_st = NULL;
029 if (Fmt->video_codec! = Codec_id_none) {
030 Video_st = Add_video_stream (OC, FMT->VIDEO_CODEC);
031}
032 if (fmt->audio_codec! = Codec_id_none) {
033 Audio_st = Add_audio_stream (OC, FMT->AUDIO_CODEC);
034}
/* Set the output parameters (must is done even if no parameters). */
035 if (av_set_parameters (OC, NULL) < 0) {
036 fprintf (stderr, "Invalid output Format parameters\n");
037 exit (1);
038}

039 dump_format (OC, 0, filename, 1);

/* Now is the all the parameters is set, we can open the audio and
Video codecs and allocate the necessary encode buffers * *
040 if (Video_st)
041 open_video (OC, Video_st);
042 if (audio_st)
043 Open_audio (OC, Audio_st);

/* Open the output file, if needed */
044 if (! ( Fmt->flags & Avfmt_nofile)) {
045 if (Url_fopen (&AMP;OC-&GT;PB, filename, url_wronly) < 0) {
046 fprintf (stderr, "Could not open '%s ' \ n", filename);
047 exit (1);
048}
049}

/* Write the stream header, if any */
050 Av_write_header (OC);

051 for (;;) {
/* Compute current audio and video time */
052 if (Audio_st)
053 audio_pts = (double) audio_st->pts.val * audio_st->time_base.num/audio_st->time_base.den;
054 Else
055 audio_pts = 0.0;

056 if (video_st)
057 video_pts = (double) video_st->pts.val * video_st->time_base.num/video_st->time_base.den;
058 Else
059 video_pts = 0.0;

060 if ((!audio_st | | audio_pts >= stream_duration) &&
061 (!video_st | | video_pts >= stream_duration))
062 break;

/* Write interleaved audio and video frames */
063 if (!video_st | | (Video_st && audio_st && audio_pts < video_pts)) {
064 write_audio_frame (OC, Audio_st);
065} else {
066 Write_video_frame (OC, Video_st);
067}
068}

/* Write the trailer, if any. The trailer must be written
* Before you close the codeccontexts open if you wrote the
* HEADER; Otherwise write_trailer may try to use memory that
* Was freed on av_codec_close () */
069 Av_write_trailer (OC);

/* Close each codec */
070 if (Video_st)
071 Close_video (OC, Video_st);
072 if (audio_st)
073 Close_audio (OC, Audio_st);

/* Free the streams * *
074 for (i = 0; i < oc->nb_streams; i++) {
075 Av_freep (&AMP;OC-&GT;STREAMS[I]-&GT;CODEC);
076 Av_freep (&oc->streams[i]);
077}

078 if (! ( Fmt->flags & Avfmt_nofile)) {
079/* Close the output file */
080 Url_fclose (OC-&GT;PB);
081}

082/* Free the stream * *
083 Av_free (OC);