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作者: www.ChinaFFmpeg.com 孙悟空
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- gcc -g doc/examples/demuxing.c -o demuxing -lavcodec -lavdevice -lavfilter -lavformat -lavutil -lswscale -lswresample -lpostproc -lx264 -lmp3lame -lz -liconv -lbz2
复制代码 测试后的情况如图
- #include <libavutil/imgutils.h>
- #include <libavutil/samplefmt.h>
- #include <libavutil/timestamp.h>
- #include <libavformat/avformat.h>
- #include <libswscale/swscale.h>
- static AVFormatContext *fmt_ctx = NULL;
- static AVCodecContext *video_dec_ctx = NULL, *audio_dec_ctx;
- static AVStream *video_stream = NULL, *audio_stream = NULL;
- static const char *src_filename = NULL;
- static const char *video_dst_filename = NULL;
- static const char *audio_dst_filename = NULL;
- static FILE *video_dst_file = NULL;
- static FILE *audio_dst_file = NULL;
- static uint8_t *video_dst_data[4] = {NULL};
- static int video_dst_linesize[4];
- static int video_dst_bufsize;
- static int video_stream_idx = -1, audio_stream_idx = -1;
- static AVFrame *frame = NULL;
- static AVPacket pkt;
- static int video_frame_count = 0;
- static int audio_frame_count = 0;
- static int decode_packet(int *got_frame, int cached)
- {
- int ret = 0;
- int decoded = pkt.size;
- uint8_t *dst_data[4];
- int dst_linesize[4];
- if (pkt.stream_index == video_stream_idx) {
- /* decode video frame */
- ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
- if (ret < 0) {
- fprintf(stderr, "Error decoding video frame\n");
- return ret;
- }
- if (*got_frame) {
- printf("video_frame%s n:%d coded_n:%d pts:%s\n",
- cached ? "(cached)" : "",
- video_frame_count++, frame->coded_picture_number,
- av_ts2timestr(frame->pts, &video_dec_ctx->time_base));
- /* copy decoded frame to destination buffer:
- * this is required since rawvideo expects non aligned data */
- av_image_copy(video_dst_data, video_dst_linesize,
- (const uint8_t **)(frame->data), frame->linesize,
- video_dec_ctx->pix_fmt, video_dec_ctx->width, video_dec_ctx->height);
- /* write to rawvideo file */
- fwrite(video_dst_data[0], 1, video_dst_bufsize, video_dst_file);
- }
- } else if (pkt.stream_index == audio_stream_idx) {
- /* decode audio frame */
- ret = avcodec_decode_audio4(audio_dec_ctx, frame, got_frame, &pkt);
- if (ret < 0) {
- fprintf(stderr, "Error decoding audio frame\n");
- return ret;
- }
- /* Some audio decoders decode only part of the packet, and have to be
- * called again with the remainder of the packet data.
- * Sample: fate-suite/lossless-audio/luckynight-partial.shn
- * Also, some decoders might over-read the packet. */
- decoded = FFMIN(ret, pkt.size);
- if (*got_frame) {
- size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(frame->format);
- printf("audio_frame%s n:%d nb_samples:%d pts:%s\n",
- cached ? "(cached)" : "",
- audio_frame_count++, frame->nb_samples,
- av_ts2timestr(frame->pts, &audio_dec_ctx->time_base));
- /* Write the raw audio data samples of the first plane. This works
- * fine for packed formats (e.g. AV_SAMPLE_FMT_S16). However,
- * most audio decoders output planar audio, which uses a separate
- * plane of audio samples for each channel (e.g. AV_SAMPLE_FMT_S16P).
- * In other words, this code will write only the first audio channel
- * in these cases.
- * You should use libswresample or libavfilter to convert the frame
- * to packed data. */
- fwrite(frame->extended_data[0], 1, unpadded_linesize, audio_dst_file);
- }
- }
- return decoded;
- }
- static int open_codec_context(int *stream_idx,
- AVFormatContext *fmt_ctx, enum AVMediaType type)
- {
- int ret;
- AVStream *st;
- AVCodecContext *dec_ctx = NULL;
- AVCodec *dec = NULL;
- ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
- if (ret < 0) {
- fprintf(stderr, "Could not find %s stream in input file '%s'\n",
- av_get_media_type_string(type), src_filename);
- return ret;
- } else {
- *stream_idx = ret;
- st = fmt_ctx->streams[*stream_idx];
- /* find decoder for the stream */
- dec_ctx = st->codec;
- dec = avcodec_find_decoder(dec_ctx->codec_id);
- if (!dec) {
- fprintf(stderr, "Failed to find %s codec\n",
- av_get_media_type_string(type));
- return ret;
- }
- if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
- fprintf(stderr, "Failed to open %s codec\n",
- av_get_media_type_string(type));
- return ret;
- }
- }
- return 0;
- }
- static int get_format_from_sample_fmt(const char **fmt,
- enum AVSampleFormat sample_fmt)
- {
- int i;
- struct sample_fmt_entry {
- enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
- } sample_fmt_entries[] = {
- { AV_SAMPLE_FMT_U8, "u8", "u8" },
- { AV_SAMPLE_FMT_S16, "s16be", "s16le" },
- { AV_SAMPLE_FMT_S32, "s32be", "s32le" },
- { AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
- { AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
- };
- *fmt = NULL;
- for (i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
- struct sample_fmt_entry *entry = &sample_fmt_entries[i];
- if (sample_fmt == entry->sample_fmt) {
- *fmt = AV_NE(entry->fmt_be, entry->fmt_le);
- return 0;
- }
- }
- fprintf(stderr,
- "sample format %s is not supported as output format\n",
- av_get_sample_fmt_name(sample_fmt));
- return -1;
- }
- int main (int argc, char **argv)
- {
- int ret = 0, got_frame;
- if (argc != 4) {
- fprintf(stderr, "usage: %s input_file video_output_file audio_output_file\n"
- "API example program to show how to read frames from an input file.\n"
- "This program reads frames from a file, decodes them, and writes decoded\n"
- "video frames to a rawvideo file named video_output_file, and decoded\n"
- "audio frames to a rawaudio file named audio_output_file.\n"
- "\n", argv[0]);
- exit(1);
- }
- src_filename = argv[1];
- video_dst_filename = argv[2];
- audio_dst_filename = argv[3];
- /* register all formats and codecs */
- av_register_all();
- /* open input file, and allocate format context */
- if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
- fprintf(stderr, "Could not open source file %s\n", src_filename);
- exit(1);
- }
- /* retrieve stream information */
- if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
- fprintf(stderr, "Could not find stream information\n");
- exit(1);
- }
- if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
- video_stream = fmt_ctx->streams[video_stream_idx];
- video_dec_ctx = video_stream->codec;
- video_dst_file = fopen(video_dst_filename, "wb");
- if (!video_dst_file) {
- fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
- ret = 1;
- goto end;
- }
- /* allocate image where the decoded image will be put */
- ret = av_image_alloc(video_dst_data, video_dst_linesize,
- video_dec_ctx->width, video_dec_ctx->height,
- video_dec_ctx->pix_fmt, 1);
- if (ret < 0) {
- fprintf(stderr, "Could not allocate raw video buffer\n");
- goto end;
- }
- video_dst_bufsize = ret;
- }
- if (open_codec_context(&audio_stream_idx, fmt_ctx, AVMEDIA_TYPE_AUDIO) >= 0) {
- audio_stream = fmt_ctx->streams[audio_stream_idx];
- audio_dec_ctx = audio_stream->codec;
- audio_dst_file = fopen(audio_dst_filename, "wb");
- if (!audio_dst_file) {
- fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
- ret = 1;
- goto end;
- }
- }
- /* dump input information to stderr */
- av_dump_format(fmt_ctx, 0, src_filename, 0);
- if (!audio_stream && !video_stream) {
- fprintf(stderr, "Could not find audio or video stream in the input, aborting\n");
- ret = 1;
- goto end;
- }
- frame = avcodec_alloc_frame();
- if (!frame) {
- fprintf(stderr, "Could not allocate frame\n");
- ret = AVERROR(ENOMEM);
- goto end;
- }
- /* initialize packet, set data to NULL, let the demuxer fill it */
- av_init_packet(&pkt);
- pkt.data = NULL;
- pkt.size = 0;
- if (video_stream)
- printf("Demuxing video from file '%s' into '%s'\n", src_filename, video_dst_filename);
- if (audio_stream)
- printf("Demuxing audio from file '%s' into '%s'\n", src_filename, audio_dst_filename);
- ///////////////////////////////////////////// 孙悟空 说: 这里是最关键的/////
- av_seek_frame(fmt_ctx, -1 , 20 * AV_TIME_BASE, AVSEEK_FLAG_ANY);
- ////////////////////////////////////////////////////////////////
- /* read frames from the file [url]www.chinaffmpeg.com[/url] 孙悟空*/
- while (av_read_frame(fmt_ctx, &pkt) >= 0) {
- AVPacket orig_pkt = pkt;
- do {
- ret = decode_packet(&got_frame, 0);
- if (ret < 0)
- break;
- pkt.data += ret;
- pkt.size -= ret;
- } while (pkt.size > 0);
- av_free_packet(&orig_pkt);
- }
- /* flush cached frames */
- pkt.data = NULL;
- pkt.size = 0;
- do {
- decode_packet(&got_frame, 1);
- } while (got_frame);
- printf("Demuxing succeeded.\n");
- if (video_stream) {
- printf("Play the output video file with the command:\n"
- "ffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
- av_get_pix_fmt_name(video_dec_ctx->pix_fmt), video_dec_ctx->width, video_dec_ctx->height,
- video_dst_filename);
- }
- if (audio_stream) {
- enum AVSampleFormat sfmt = audio_dec_ctx->sample_fmt;
- int n_channels = audio_dec_ctx->channels;
- const char *fmt;
- if (av_sample_fmt_is_planar(sfmt)) {
- const char *packed = av_get_sample_fmt_name(sfmt);
- printf("Warning: the sample format the decoder produced is planar "
- "(%s). This example will output the first channel only.\n",
- packed ? packed : "?");
- sfmt = av_get_packed_sample_fmt(sfmt);
- n_channels = 1;
- }
- if ((ret = get_format_from_sample_fmt(&fmt, sfmt)) < 0)
- goto end;
- printf("Play the output audio file with the command:\n"
- "ffplay -f %s -ac %d -ar %d %s\n",
- fmt, n_channels, audio_dec_ctx->sample_rate,
- audio_dst_filename);
- }
- end:
- if (video_dec_ctx)
- avcodec_close(video_dec_ctx);
- if (audio_dec_ctx)
- avcodec_close(audio_dec_ctx);
- avformat_close_input(&fmt_ctx);
- if (video_dst_file)
- fclose(video_dst_file);
- if (audio_dst_file)
- fclose(audio_dst_file);
- av_free(frame);
- av_free(video_dst_data[0]);
- return ret < 0;
- }
复制代码 |
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