ffmpeg使用C语言sdk实现抽取视频中的视频数据
主要使用函数
-
特征码：Start code
-
解码的一些视频参数，分辨率和帧率：SPS/PPS
-
ffmpeg获取SPS/PPS：codec->extradata
实例
#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avformat.h>
#ifndef AV_WB32
# define AV_WB32(p, val) do { \
uint32_t d = (val); \
((uint8_t*)(p))[3] = (d); \
((uint8_t*)(p))[2] = (d)>>8; \
((uint8_t*)(p))[1] = (d)>>16; \
((uint8_t*)(p))[0] = (d)>>24; \
} while(0)
#endif
#ifndef AV_RB16
# define AV_RB16(x) \
((((const uint8_t*)(x))[0] << 8) | \
((const uint8_t*)(x))[1])
#endif
static int alloc_and_copy(AVPacket *out,
const uint8_t *sps_pps, uint32_t sps_pps_size,
const uint8_t *in, uint32_t in_size)
{
uint32_t offset = out->size;
uint8_t nal_header_size = offset ? 3 : 4;
int err;
err = av_grow_packet(out, sps_pps_size + in_size + nal_header_size);
if (err < 0)
return err;
if (sps_pps)
memcpy(out->data + offset, sps_pps, sps_pps_size);
memcpy(out->data + sps_pps_size + nal_header_size + offset, in, in_size);
if (!offset) {
AV_WB32(out->data + sps_pps_size, 1);
} else {
(out->data + offset + sps_pps_size)[0] =
(out->data + offset + sps_pps_size)[1] = 0;
(out->data + offset + sps_pps_size)[2] = 1;
}
return 0;
}
int h264_extradata_to_annexb(const uint8_t *codec_extradata, const int codec_extradata_size, AVPacket *out_extradata, int padding)
{
uint16_t unit_size;
uint64_t total_size = 0;
uint8_t *out = NULL, unit_nb, sps_done = 0,
sps_seen = 0, pps_seen = 0, sps_offset = 0, pps_offset = 0;
const uint8_t *extradata = codec_extradata + 4;
static const uint8_t nalu_header[4] = { 0, 0, 0, 1 };
int length_size = (*extradata++ & 0x3) + 1; // retrieve length coded size, 用于指示表示编码数据长度所需字节数
sps_offset = pps_offset = -1;
/* retrieve sps and pps unit(s) */
unit_nb = *extradata++ & 0x1f; /* number of sps unit(s) */
if (!unit_nb) {
goto pps;
}else {
sps_offset = 0;
sps_seen = 1;
}
while (unit_nb--) {
int err;
unit_size = AV_RB16(extradata);
total_size += unit_size + 4;
if (total_size > INT_MAX - padding) {
av_log(NULL, AV_LOG_ERROR,
"Too big extradata size, corrupted stream or invalid MP4/AVCC bitstream\n");
av_free(out);
return AVERROR(EINVAL);
}
if (extradata + 2 + unit_size > codec_extradata + codec_extradata_size) {
av_log(NULL, AV_LOG_ERROR, "Packet header is not contained in global extradata, "
"corrupted stream or invalid MP4/AVCC bitstream\n");
av_free(out);
return AVERROR(EINVAL);
}
if ((err = av_reallocp(&out, total_size + padding)) < 0)
return err;
memcpy(out + total_size - unit_size - 4, nalu_header, 4);
memcpy(out + total_size - unit_size, extradata + 2, unit_size);
extradata += 2 + unit_size;
pps:
if (!unit_nb && !sps_done++) {
unit_nb = *extradata++; /* number of pps unit(s) */
if (unit_nb) {
pps_offset = total_size;
pps_seen = 1;
}
}
}
if (out)
memset(out + total_size, 0, padding);
if (!sps_seen)
av_log(NULL, AV_LOG_WARNING,
"Warning: SPS NALU missing or invalid. "
"The resulting stream may not play.\n");
if (!pps_seen)
av_log(NULL, AV_LOG_WARNING,
"Warning: PPS NALU missing or invalid. "
"The resulting stream may not play.\n");
out_extradata->data = out;
out_extradata->size = total_size;
return length_size;
}
int h264_mp4toannexb(AVFormatContext *fmt_ctx, AVPacket *in, FILE *dst_fd)
{
AVPacket *out = NULL;
AVPacket spspps_pkt;
int len;
uint8_t unit_type;
int32_t nal_size;
uint32_t cumul_size = 0;
const uint8_t *buf;
const uint8_t *buf_end;
int buf_size;
int ret = 0, i;
out = av_packet_alloc();
buf = in->data;
buf_size = in->size;
buf_end = in->data + in->size;
do {
ret= AVERROR(EINVAL);
if (buf + 4 /*s->length_size*/ > buf_end)
goto fail;
for (nal_size = 0, i = 0; i<4/*s->length_size*/; i++)
nal_size = (nal_size << 8) | buf[i];
buf += 4; /*s->length_size;*/
unit_type = *buf & 0x1f;
unit_type = *buf & 0x1f
if (nal_size > buf_end - buf || nal_size < 0)
goto fail;
/*
if (unit_type == 7)
s->idr_sps_seen = s->new_idr = 1;
else if (unit_type == 8) {
s->idr_pps_seen = s->new_idr = 1;
*/
/* if SPS has not been seen yet, prepend the AVCC one to PPS */
/*
if (!s->idr_sps_seen) {
if (s->sps_offset == -1)
av_log(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable\n");
else {
if ((ret = alloc_and_copy(out,
ctx->par_out->extradata + s->sps_offset,
s->pps_offset != -1 ? s->pps_offset : ctx->par_out->extradata_size - s->sps_offset,
buf, nal_size)) < 0)
goto fail;
s->idr_sps_seen = 1;
goto next_nal;
}
}
}
*/
/* if this is a new IDR picture following an IDR picture, reset the idr flag.
* Just check first_mb_in_slice to be 0 as this is the simplest solution.
* This could be checking idr_pic_id instead, but would complexify the parsing. */
/*
if (!s->new_idr && unit_type == 5 && (buf[1] & 0x80))
s->new_idr = 1;
*/
/* prepend only to the first type 5 NAL unit of an IDR picture, if no sps/pps are already present */
if (/*s->new_idr && */unit_type == 5 /*&& !s->idr_sps_seen && !s->idr_pps_seen*/) {
h264_extradata_to_annexb( fmt_ctx->streams[in->stream_index]->codec->extradata,
fmt_ctx->streams[in->stream_index]->codec->extradata_size,
&spspps_pkt,
AV_INPUT_BUFFER_PADDING_SIZE);
if ((ret=alloc_and_copy(out,
spspps_pkt.data, spspps_pkt.size,
buf, nal_size)) < 0)
goto fail;
/*s->new_idr = 0;*/
/* if only SPS has been seen, also insert PPS */
}
/*else if (s->new_idr && unit_type == 5 && s->idr_sps_seen && !s->idr_pps_seen) {
if (s->pps_offset == -1) {
av_log(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
goto fail;
} else if ((ret = alloc_and_copy(out,
ctx->par_out->extradata + s->pps_offset, ctx->par_out->extradata_size - s->pps_offset,
buf, nal_size)) < 0)
goto fail;
}*/ else {
if ((ret=alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
goto fail;
/*
if (!s->new_idr && unit_type == 1) {
s->new_idr = 1;
s->idr_sps_seen = 0;
s->idr_pps_seen = 0;
}
*/
}
len = fwrite( out->data, 1, out->size, dst_fd);
if(len != out->size){
av_log(NULL, AV_LOG_DEBUG, "warning, length of writed data isn't equal pkt.size(%d, %d)\n",
len,
out->size);
}
fflush(dst_fd);
next_nal:
buf += nal_size;
cumul_size += nal_size + 4;//s->length_size;
} while (cumul_size < buf_size);
/*
ret = av_packet_copy_props(out, in);
if (ret < 0)
goto fail;
*/
fail:
av_packet_free(&out);
return ret;
}
int main(int argc, char argv[]){
int err_code;
char errors[1024];
char *src_filename = NULL;
char *dst_filename = NULL;
FILE *dst_fd = NULL;
int video_stream_index = -1;
// 创建文件上下文，和包管理
AVFormatContext *fmt_ctx = NULL;
AVPacket pkt;
// 设置日志等级
av_log_set_level(AV_LOG_DEBUG);
// 判断参数个数
if (argc < 3){
av_log(NULL, AV_LOG_DEBUG, "参数不足");
return -1
}
// 输出输出文件
src_filename = argv[1];
dst_filename = argv[2];
// 判断参数不可以为空
if (src_filename == NULL || dst_filename == NULL){
av_log(NULL, AV_LOG_ERROR, "传入的参数不可以为空");
return -1;
}
// 全局注册函数
av_register_all();
// 打开目标文件
dst_fd = fopen(dst_filename, "wb");
if (!dst_fd){
av_log(NULL, AV_LOG_DEBUG, "不能打开文件%s", dst_filename);
return -1;
}
// 读取流文件
if ((err_code=avformat_open_input(&fmt_ctx, src_filename, NULL, NULL))<0){
// 设置错误信息
av_strerror(err_code, errors, 1024);
// 打印日志输出
av_log(NULL, AV_LOG_DEBUG, "流文件读取失败: %s, %d(%s)\n",
src_filename,
err_code,
errors;);
return -1;
}
av_dump_format(fmt_ctx, 0 , src_filename, 0);
// 数据包处理
av_init_packet(&pkt);
pkt.data=NULL;
pkt.size = 0;
// 找到最好的流
video_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
if (video_stream_index<0){
av_log(NULL, AV_LOG_DEBUG, "不能找到流输出", av_get_media_type_string(AVMEDIA_TYPE_VIDEO),
src_filename);
return AVERROR(EINVAL);
}
// 拿到视频的index，去视频流中去取一个一个包文件
while (av_read_frame(fmt_ctx, &pkt) >= 0){
if(pkt.stream_index == video_stream_index){
// 处理h264处理函数
h264_mp4toannexb(fmt_ctx, &pkt, dst_fd);
}
av_packet_unref(&pkt);
}
// 关闭流文件
avformat_close_input(&fmt_ctx);
if(dst_fd){
fclose(dst_fd);
}
return 0;
}
