ffmpeg中av_seek_frame使用样例(代码实现)

av_seek_frame使用时需要使用四个参数 av_seek_frame(fmt_ctx, -1 , 20 * AV_TIME_BASE, AVSEEK_FLAG_ANY); 参数一: fmt_ctx为容器内容; 参数二: 流索引, stream_index 参数三: 将要定位处的时间戳 参数四: seek功能flag 容器即AVFormatContext, 其中包含了一些视频标准格式中对应的封装信息，例如stream个数，stream类型，AVCodec，字幕信息等； stream_index，容器中包含了stream，有音频stream，视频stream，3D的电影有多个视频stream，subtitle stream等stream信息。 那么如果需要seek到对应的时间戳处需要考虑几个问题： 1. 得到AVFormatContext信息 2. 需要得到stream_index信息 3. 需要设定将要定位的时间戳信息 4. seek功能需要根据需求设置 结合上述四点，可以实现代码步骤如下： av_register_all(); avformat_open_input avformat_find_stream_info open_codec_context av_seek_frame 以上为简单的seek步骤，当然细节部分，还要有一些操作，例如avpackets相关的操作等 下面测试用例编译命令为

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1. gcc -g doc/examples/demuxing.c -o demuxing -lavcodec -lavdevice -lavfilter -lavformat -lavutil -lswscale -lswresample -lpostproc -lx264 -lmp3lame -lz -liconv -lbz2

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1. #include <libavutil/imgutils.h>
2. #include <libavutil/samplefmt.h>
3. #include <libavutil/timestamp.h>
4. #include <libavformat/avformat.h>
5. #include <libswscale/swscale.h>
7. static AVFormatContext *fmt_ctx = NULL;
8. static AVCodecContext *video_dec_ctx = NULL, *audio_dec_ctx;
9. static AVStream *video_stream = NULL, *audio_stream = NULL;
10. static const char *src_filename = NULL;
11. static const char *video_dst_filename = NULL;
12. static const char *audio_dst_filename = NULL;
13. static FILE *video_dst_file = NULL;
14. static FILE *audio_dst_file = NULL;
16. static uint8_t *video_dst_data[4] = {NULL};
17. static int video_dst_linesize[4];
18. static int video_dst_bufsize;
20. static int video_stream_idx = -1, audio_stream_idx = -1;
21. static AVFrame *frame = NULL;
22. static AVPacket pkt;
23. static int video_frame_count = 0;
24. static int audio_frame_count = 0;
26. static int decode_packet(int *got_frame, int cached)
27. {
28. int ret = 0;
29. int decoded = pkt.size;
30.     uint8_t *dst_data[4];
31. int dst_linesize[4];
32. if (pkt.stream_index == video_stream_idx) {
33. /* decode video frame */
34.         ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
35. if (ret < 0) {
36.             fprintf(stderr, "Error decoding video frame\n");
37.             return ret;
38. }
40. if (*got_frame) {
41.             printf("video_frame%s n:%d coded_n:%d pts:%s\n",
42.                    cached ? "(cached)" : "",
43.                    video_frame_count++, frame->coded_picture_number,
44.                    av_ts2timestr(frame->pts, &video_dec_ctx->time_base));
46. /* copy decoded frame to destination buffer:
47. * this is required since rawvideo expects non aligned data */
48.             av_image_copy(video_dst_data, video_dst_linesize,
49. (const uint8_t **)(frame->data), frame->linesize,
50.                           video_dec_ctx->pix_fmt, video_dec_ctx->width, video_dec_ctx->height);
52. /* write to rawvideo file */
53.             fwrite(video_dst_data[0], 1, video_dst_bufsize, video_dst_file);
54. }
55. } else if (pkt.stream_index == audio_stream_idx) {
56. /* decode audio frame */
57.         ret = avcodec_decode_audio4(audio_dec_ctx, frame, got_frame, &pkt);
58. if (ret < 0) {
59.             fprintf(stderr, "Error decoding audio frame\n");
60.             return ret;
61. }
62. /* Some audio decoders decode only part of the packet, and have to be
63. * called again with the remainder of the packet data.
64. * Sample: fate-suite/lossless-audio/luckynight-partial.shn
65. * Also, some decoders might over-read the packet. */
66.         decoded = FFMIN(ret, pkt.size);
68. if (*got_frame) {
69.             size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(frame->format);
70.             printf("audio_frame%s n:%d nb_samples:%d pts:%s\n",
71.                    cached ? "(cached)" : "",
72.                    audio_frame_count++, frame->nb_samples,
73.                    av_ts2timestr(frame->pts, &audio_dec_ctx->time_base));
75. /* Write the raw audio data samples of the first plane. This works
76. * fine for packed formats (e.g. AV_SAMPLE_FMT_S16). However,
77. * most audio decoders output planar audio, which uses a separate
78. * plane of audio samples for each channel (e.g. AV_SAMPLE_FMT_S16P).
79. * In other words, this code will write only the first audio channel
80. * in these cases.
81. * You should use libswresample or libavfilter to convert the frame
82. * to packed data. */
83.             fwrite(frame->extended_data[0], 1, unpadded_linesize, audio_dst_file);
84. }
85. }
86.     return decoded;
87. }
89. static int open_codec_context(int *stream_idx,
90.                               AVFormatContext *fmt_ctx, enum AVMediaType type)
91. {
92. int ret;
93.     AVStream *st;
94.     AVCodecContext *dec_ctx = NULL;
95.     AVCodec *dec = NULL;
97.     ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
98. if (ret < 0) {
99.         fprintf(stderr, "Could not find %s stream in input file '%s'\n",
100.                 av_get_media_type_string(type), src_filename);
101.         return ret;
102. } else {
103. *stream_idx = ret;
104.         st = fmt_ctx->streams[*stream_idx];
106. /* find decoder for the stream */
107.         dec_ctx = st->codec;
108.         dec = avcodec_find_decoder(dec_ctx->codec_id);
109. if (!dec) {
110.             fprintf(stderr, "Failed to find %s codec\n",
111.                     av_get_media_type_string(type));
112.             return ret;
113. }
115. if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
116.             fprintf(stderr, "Failed to open %s codec\n",
117.                     av_get_media_type_string(type));
118.             return ret;
119. }
120. }
122.     return 0;
123. }
125. static int get_format_from_sample_fmt(const char **fmt,
126.                                       enum AVSampleFormat sample_fmt)
127. {
128. int i;
129.     struct sample_fmt_entry {
130.         enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
131. } sample_fmt_entries[] = {
132. { AV_SAMPLE_FMT_U8, "u8", "u8" },
133. { AV_SAMPLE_FMT_S16, "s16be", "s16le" },
134. { AV_SAMPLE_FMT_S32, "s32be", "s32le" },
135. { AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
136. { AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
137. };
138. *fmt = NULL;
140. for (i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
141.         struct sample_fmt_entry *entry = &sample_fmt_entries[i];
142. if (sample_fmt == entry->sample_fmt) {
143. *fmt = AV_NE(entry->fmt_be, entry->fmt_le);
144.             return 0;
145. }
146. }
148.     fprintf(stderr,
149. "sample format %s is not supported as output format\n",
150.             av_get_sample_fmt_name(sample_fmt));
151.     return -1;
152. }
154. int main (int argc, char **argv)
155. {
156. int ret = 0, got_frame;
158. if (argc != 4) {
159.         fprintf(stderr, "usage: %s input_file video_output_file audio_output_file\n"
160. "API example program to show how to read frames from an input file.\n"
161. "This program reads frames from a file, decodes them, and writes decoded\n"
162. "video frames to a rawvideo file named video_output_file, and decoded\n"
163. "audio frames to a rawaudio file named audio_output_file.\n"
164. "\n", argv[0]);
165. exit(1);
166. }
167.     src_filename = argv[1];
168.     video_dst_filename = argv[2];
169.     audio_dst_filename = argv[3];
171. /* register all formats and codecs */
172.     av_register_all();
174. /* open input file, and allocate format context */
175. if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
176.         fprintf(stderr, "Could not open source file %s\n", src_filename);
177. exit(1);
178. }
180. /* retrieve stream information */
181. if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
182.         fprintf(stderr, "Could not find stream information\n");
183. exit(1);
184. }
186. if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
187.         video_stream = fmt_ctx->streams[video_stream_idx];
188.         video_dec_ctx = video_stream->codec;
190.         video_dst_file = fopen(video_dst_filename, "wb");
191. if (!video_dst_file) {
192.             fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
193.             ret = 1;
194.             goto end;
195. }
197. /* allocate image where the decoded image will be put */
198.         ret = av_image_alloc(video_dst_data, video_dst_linesize,
199.                              video_dec_ctx->width, video_dec_ctx->height,
200.                              video_dec_ctx->pix_fmt, 1);
201. if (ret < 0) {
202.             fprintf(stderr, "Could not allocate raw video buffer\n");
203.             goto end;
204. }
205.         video_dst_bufsize = ret;
206. }
208. if (open_codec_context(&audio_stream_idx, fmt_ctx, AVMEDIA_TYPE_AUDIO) >= 0) {
209.         audio_stream = fmt_ctx->streams[audio_stream_idx];
210.         audio_dec_ctx = audio_stream->codec;
211.         audio_dst_file = fopen(audio_dst_filename, "wb");
212. if (!audio_dst_file) {
213.             fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
214.             ret = 1;
215.             goto end;
216. }
217. }
219. /* dump input information to stderr */
220.     av_dump_format(fmt_ctx, 0, src_filename, 0);
222. if (!audio_stream && !video_stream) {
223.         fprintf(stderr, "Could not find audio or video stream in the input, aborting\n");
224.         ret = 1;
225.         goto end;
226. }
228.     frame = avcodec_alloc_frame();
229. if (!frame) {
230.         fprintf(stderr, "Could not allocate frame\n");
231.         ret = AVERROR(ENOMEM);
232.         goto end;
233. }
235. /* initialize packet, set data to NULL, let the demuxer fill it */
236.     av_init_packet(&pkt);
237.     pkt.data = NULL;
238.     pkt.size = 0;
240. if (video_stream)
241.         printf("Demuxing video from file '%s' into '%s'\n", src_filename, video_dst_filename);
242. if (audio_stream)
243.         printf("Demuxing audio from file '%s' into '%s'\n", src_filename, audio_dst_filename);
245. ///////////////////////////////////////////// 孙悟空 说： 这里是最关键的/////
246.     av_seek_frame(fmt_ctx, -1 , 20 * AV_TIME_BASE, AVSEEK_FLAG_ANY);
247. ////////////////////////////////////////////////////////////////
248. /* read frames from the file [url]www.chinaffmpeg.com[/url] 孙悟空*/
249. while (av_read_frame(fmt_ctx, &pkt) >= 0) {
250.         AVPacket orig_pkt = pkt;
251. do {
252.             ret = decode_packet(&got_frame, 0);
253. if (ret < 0)
254.                 break;
255.             pkt.data += ret;
256.             pkt.size -= ret;
257. } while (pkt.size > 0);
258.         av_free_packet(&orig_pkt);
259. }
261. /* flush cached frames */
262.     pkt.data = NULL;
263.     pkt.size = 0;
264. do {
265.         decode_packet(&got_frame, 1);
266. } while (got_frame);
268.     printf("Demuxing succeeded.\n");
270. if (video_stream) {
271.         printf("Play the output video file with the command:\n"
272. "ffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
273.                av_get_pix_fmt_name(video_dec_ctx->pix_fmt), video_dec_ctx->width, video_dec_ctx->height,
274.                video_dst_filename);
275. }
277. if (audio_stream) {
278.         enum AVSampleFormat sfmt = audio_dec_ctx->sample_fmt;
279. int n_channels = audio_dec_ctx->channels;
280. const char *fmt;
282. if (av_sample_fmt_is_planar(sfmt)) {
283. const char *packed = av_get_sample_fmt_name(sfmt);
284.             printf("Warning: the sample format the decoder produced is planar "
285. "(%s). This example will output the first channel only.\n",
286.                    packed ? packed : "?");
287.             sfmt = av_get_packed_sample_fmt(sfmt);
288.             n_channels = 1;
289. }
291. if ((ret = get_format_from_sample_fmt(&fmt, sfmt)) < 0)
292.             goto end;
294.         printf("Play the output audio file with the command:\n"
295. "ffplay -f %s -ac %d -ar %d %s\n",
296.                fmt, n_channels, audio_dec_ctx->sample_rate,
297.                audio_dst_filename);
298. }
300. end:
301. if (video_dec_ctx)
302.         avcodec_close(video_dec_ctx);
303. if (audio_dec_ctx)
304.         avcodec_close(audio_dec_ctx);
305.     avformat_close_input(&fmt_ctx);
306. if (video_dst_file)
307.         fclose(video_dst_file);
308. if (audio_dst_file)
309.         fclose(audio_dst_file);
310.     av_free(frame);
311.     av_free(video_dst_data[0]);
313.     return ret < 0;
314. }

测试结果