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Surat[email protected]
2024-07-12
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File MP4 adalah format wadah multimedia yang dapat berisi berbagai jenis data audio dan video, termasuk video H.264. File MP4 menggunakan struktur hierarki yang disebut "kotak" atau "atom" untuk mengatur data. Setiap kotak memiliki fungsi dan tujuan tertentu untuk menyimpan metadata file, data audio dan video, serta informasi lainnya.
File MP4 terdiri dari beberapa kotak, setiap kotak memiliki header dan konten (payload). Hirarki kotak memungkinkan file MP4 menyimpan dan mengatur data secara fleksibel. Kotak umum meliputi:
Data video H.264 biasanya disimpan dimelacakdi dalam kotak, khususnya dimdia(media),menit(informasi media),stbl subkotak (Tabel Contoh). Berikut ini adalah rincian metode penyimpanannya:
ftypKotak tersebut berisi jenis file dan informasi kompatibilitas yang menunjukkan format dan versi file.
moovKotak berisi metadata global, termasuk subkotak utama berikut:
mdat Kotak tersebut berisi data media aktual, termasuk data video H.264. Ini berbeda dengan format Annex-B.Data video biasanya tidak berisi kode awal unit NAL, namun menggunakan bidang panjang.
stsdInformasi terperinci tentang aliran H.264, termasuk data SPS dan PPS, disimpan di (kotak deskripsi contoh):
Bidang kode awal vs panjang：
lengthSizeMinusOne Tentukan, biasanya 4 byte.0x00000001 atau0x000001, digunakan untuk mengidentifikasi batas-batas unit NAL.Penyimpanan data SPS dan PPS：
AVCDecoderConfigurationRecord , dan diurai saat dekoder diinisialisasi.menggunakan：
#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;
}
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Surat[email protected]