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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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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#include <libavutil/imgutils.h>
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#include <libavutil/samplefmt.h>
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#include <libavutil/timestamp.h>
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#include <libavformat/avformat.h>
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#include <libswscale/swscale.h>
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-
static AVFormatContext *fmt_ctx = NULL;
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static AVCodecContext *video_dec_ctx = NULL, *audio_dec_ctx;
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static AVStream *video_stream = NULL, *audio_stream = NULL;
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static const char *src_filename = NULL;
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static const char *video_dst_filename = NULL;
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static const char *audio_dst_filename = NULL;
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static FILE *video_dst_file = NULL;
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static FILE *audio_dst_file = NULL;
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-
static uint8_t *video_dst_data[4] = {NULL};
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static int video_dst_linesize[4];
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static int video_dst_bufsize;
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-
static int video_stream_idx = -1, audio_stream_idx = -1;
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static AVFrame *frame = NULL;
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static AVPacket pkt;
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static int video_frame_count = 0;
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static int audio_frame_count = 0;
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-
static int decode_packet(int *got_frame, int cached)
-
{
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int ret = 0;
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int decoded = pkt.size;
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uint8_t *dst_data[4];
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int dst_linesize[4];
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if (pkt.stream_index == video_stream_idx) {
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/* decode video frame */
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ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
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if (ret < 0) {
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fprintf(stderr, "Error decoding video frame\n");
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return ret;
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}
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-
if (*got_frame) {
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printf("video_frame%s n:%d coded_n:%d pts:%s\n",
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cached ? "(cached)" : "",
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video_frame_count++, frame->coded_picture_number,
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av_ts2timestr(frame->pts, &video_dec_ctx->time_base));
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/* copy decoded frame to destination buffer:
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* this is required since rawvideo expects non aligned data */
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av_image_copy(video_dst_data, video_dst_linesize,
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(const uint8_t **)(frame->data), frame->linesize,
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video_dec_ctx->pix_fmt, video_dec_ctx->width, video_dec_ctx->height);
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-
/* write to rawvideo file */
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fwrite(video_dst_data[0], 1, video_dst_bufsize, video_dst_file);
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}
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} else if (pkt.stream_index == audio_stream_idx) {
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/* decode audio frame */
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ret = avcodec_decode_audio4(audio_dec_ctx, frame, got_frame, &pkt);
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if (ret < 0) {
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fprintf(stderr, "Error decoding audio frame\n");
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return ret;
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}
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/* Some audio decoders decode only part of the packet, and have to be
-
* called again with the remainder of the packet data.
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* Sample: fate-suite/lossless-audio/luckynight-partial.shn
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* Also, some decoders might over-read the packet. */
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decoded = FFMIN(ret, pkt.size);
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-
if (*got_frame) {
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size_t unpadded_linesize = frame->nb_samples * av_get_bytes_per_sample(frame->format);
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printf("audio_frame%s n:%d nb_samples:%d pts:%s\n",
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cached ? "(cached)" : "",
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audio_frame_count++, frame->nb_samples,
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av_ts2timestr(frame->pts, &audio_dec_ctx->time_base));
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/* Write the raw audio data samples of the first plane. This works
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* fine for packed formats (e.g. AV_SAMPLE_FMT_S16). However,
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* most audio decoders output planar audio, which uses a separate
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* plane of audio samples for each channel (e.g. AV_SAMPLE_FMT_S16P).
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* In other words, this code will write only the first audio channel
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* in these cases.
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* You should use libswresample or libavfilter to convert the frame
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* to packed data. */
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fwrite(frame->extended_data[0], 1, unpadded_linesize, audio_dst_file);
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}
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}
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return decoded;
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}
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static int open_codec_context(int *stream_idx,
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AVFormatContext *fmt_ctx, enum AVMediaType type)
-
{
-
int ret;
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AVStream *st;
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AVCodecContext *dec_ctx = NULL;
-
AVCodec *dec = NULL;
-
-
ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
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if (ret < 0) {
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fprintf(stderr, "Could not find %s stream in input file '%s'\n",
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av_get_media_type_string(type), src_filename);
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return ret;
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} else {
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*stream_idx = ret;
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st = fmt_ctx->streams[*stream_idx];
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/* find decoder for the stream */
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dec_ctx = st->codec;
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dec = avcodec_find_decoder(dec_ctx->codec_id);
-
if (!dec) {
-
fprintf(stderr, "Failed to find %s codec\n",
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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",
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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,
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"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"
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"API example program to show how to read frames from an input file.\n"
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"This program reads frames from a file, decodes them, and writes decoded\n"
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"video frames to a rawvideo file named video_output_file, and decoded\n"
-
"audio frames to a rawaudio file named audio_output_file.\n"
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"\n", argv[0]);
-
exit(1);
-
}
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src_filename = argv[1];
-
video_dst_filename = argv[2];
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audio_dst_filename = argv[3];
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-
/* register all formats and codecs */
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av_register_all();
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-
/* open input file, and allocate format context */
-
if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
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fprintf(stderr, "Could not open source file %s\n", src_filename);
-
exit(1);
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}
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/* retrieve stream information */
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if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
-
fprintf(stderr, "Could not find stream information\n");
-
exit(1);
-
}
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-
if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
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video_stream = fmt_ctx->streams[video_stream_idx];
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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;
-
}
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-
/* allocate image where the decoded image will be put */
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ret = av_image_alloc(video_dst_data, video_dst_linesize,
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video_dec_ctx->width, video_dec_ctx->height,
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video_dec_ctx->pix_fmt, 1);
-
if (ret < 0) {
-
fprintf(stderr, "Could not allocate raw video buffer\n");
-
goto end;
-
}
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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);
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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;
-
}
测试结果
孙悟空
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