2024-07-12
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MP4 सञ्चिका बहुमाध्यमपात्रस्वरूपम् अस्ति यस्मिन् H.264 विडियो सहितं बहुविधं श्रव्यं, भिडियो च दत्तांशं भवितुं शक्नोति । MP4 सञ्चिकाः दत्तांशं व्यवस्थित्यै "boxes" अथवा "atoms" इति श्रेणीबद्धसंरचनायाः उपयोगं कुर्वन्ति । प्रत्येकं पेटीयां सञ्चिकामेटाडाटा, श्रव्य-वीडियो-दत्तांशः, अन्यसूचनाः च संग्रहीतुं विशिष्टं कार्यं प्रयोजनं च भवति ।
MP4 सञ्चिकाः बहुभिः पेटीभिः निर्मिताः भवन्ति, प्रत्येकं पेटीयां शीर्षकं सामग्री च (पेलोड्) भवति । पेटीनां श्रेणीक्रमेण MP4 सञ्चिकाः लचीलेन आँकडानां संग्रहणं व्यवस्थितीकरणं च कर्तुं शक्नुवन्ति । सामान्यपेटिकासु अन्तर्भवन्ति : १.
H.264 विडियो दत्तांशः सामान्यतया अत्र संगृह्यतेत्रक्पेटीयां विशेषतया इmdia(माध्यम), २.minf(माध्यमसूचना), २.stbl (उदाहरण सारणी) उपपेटी। विस्तृतः भण्डारणविधिः निम्नलिखितम् अस्ति ।
ftypपेटीयां सञ्चिकास्वरूपं संस्करणं च सूचयन्त्याः सञ्चिकाप्रकारः संगततासूचना च भवति ।
moovपेटीषु वैश्विकमेटाडाटा भवति, यत्र निम्नलिखितमुख्य-उप-पेटिकाः सन्ति ।
mdat पेटीयां वास्तविकं माध्यमदत्तांशं भवति, यत्र H.264 विडियोदत्तांशः अपि अस्ति । एतत् अनुलग्नक-ख-स्वरूपात् भिन्नम् अस्ति ।विडियो दत्तांशे प्रायः NAL यूनिट् स्टार्ट् कोड् न भवति, परन्तु लम्बताक्षेत्रस्य उपयोगः भवति ।
stsdSPS तथा PPS आँकडा सहित H.264 धारा विषये विस्तृतसूचना (नमूना विवरणपेटिका) मध्ये संगृहीता अस्ति:
कोड बनाम लम्बता क्षेत्रं आरभ्यताम्：
lengthSizeMinusOne निर्धारयन्तु, प्रायः ४ बाइट् ।0x00000001 वा0x000001, एनएएल-एककानां सीमानां परिचयार्थं प्रयुक्तम् ।SPS तथा PPS आँकडा भण्डारणम्：
AVCDecoderConfigurationRecord , तथा च डिकोडरस्य आरम्भे विश्लेषणं भवति ।उपयुञ्जताम्：
#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avio.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
//读取内存中以大端字节序（big-endian）存储的16位无符号整数
#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;
}
//将 H.264 编码器的 extradata (额外数据)，从 MP4/AVCC 格式转换为 Annex-B 格式，并将其存储在 AVPacket 结构中。
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;
// 跳过AVCC 格式中的前四个字节，这些信息在解析NAL单元的时候并不需要
static const uint8_t nalu_header[4] = { 0, 0, 0, 1 }; //填充起始码
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 bitstreamn");
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 bitstreamn");
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;
}
//将MP4中的AVCC格式转为annexb格式
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; //确定单元类型
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 unreadablen");
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*/) {
//说明是个关键帧，需要将MP4中的SPS/PPS 填充到NAL单元之前
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 unreadablen");
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;
//AVFormatContext *ofmt_ctx = NULL;
//AVOutputFormat *output_fmt = NULL;
//AVStream *out_stream = NULL;
AVFormatContext *fmt_ctx = NULL;
AVPacket pkt;
//AVFrame *frame = NULL;
av_log_set_level(AV_LOG_DEBUG);
if(argc < 3){
av_log(NULL, AV_LOG_DEBUG, "the count of parameters should be more than three!n");
return -1;
}
src_filename = argv[1];
dst_filename = argv[2];
if(src_filename == NULL || dst_filename == NULL){
av_log(NULL, AV_LOG_ERROR, "src or dts file is null, plz check them!n");
return -1;
}
/*register all formats and codec*/
av_register_all();
dst_fd = fopen(dst_filename, "wb");
if (!dst_fd) {
av_log(NULL, AV_LOG_DEBUG, "Could not open destination file %sn", dst_filename);
return -1;
}
/*open input media file, and allocate format context*/
if((err_code = avformat_open_input(&fmt_ctx, src_filename, NULL, NULL)) < 0){
av_strerror(err_code, errors, 1024);
av_log(NULL, AV_LOG_DEBUG, "Could not open source file: %s, %d(%s)n",
src_filename,
err_code,
errors);
return -1;
}
/*dump input information*/
av_dump_format(fmt_ctx, 0, src_filename, 0);
/*initialize packet*/
av_init_packet(&pkt);
pkt.data = NULL;
pkt.size = 0;
/*find best video stream*/
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, "Could not find %s stream in input file %sn",
av_get_media_type_string(AVMEDIA_TYPE_VIDEO),
src_filename);
return AVERROR(EINVAL);
}
/*
if (avformat_write_header(ofmt_ctx, NULL) < 0) {
av_log(NULL, AV_LOG_DEBUG, "Error occurred when opening output file");
exit(1);
}
*/
/*read frames from media file*/
while(av_read_frame(fmt_ctx, &pkt) >=0 ){
if(pkt.stream_index == video_stream_index){
/*
pkt.stream_index = 0;
av_write_frame(ofmt_ctx, &pkt);
av_free_packet(&pkt);
*/
h264_mp4toannexb(fmt_ctx, &pkt, dst_fd);
}
//release pkt->data
av_packet_unref(&pkt);
}
//av_write_trailer(ofmt_ctx);
/*close input media file*/
avformat_close_input(&fmt_ctx);
if(dst_fd) {
fclose(dst_fd);
}
//avio_close(ofmt_ctx->pb);
return 0;
}
सः ३० वर्षाणाम् अनुसरणं प्रौयोगिक क्रमबद्धता युक्तं, आलंकार, जावा, जावास्विस्च, ph, css, सद्भावना संस्कृती, ph, css निर्वहनशील भाषा सुनावंश, ससरोत विद्वान विपक्षी विद्वान विनियोग विनियोग विनियोग विनियोग्य विवेचन विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग विनियोग
