segcation fault而avcodec_encode_video2 [英] segmetation fault while avcodec_encode_video2
问题描述
在尝试将AVFrame编码到数据包时，我遇到了一些问题。
在读取整个代码之前，输入的内容正在工作，我测试了它。输出内容来自示例。
最后我解决了我的问题。
问题是（除了libav的文档）avpacket不是图片在包中的副本。它只是指向数据包的数据。你必须做一个副本，或者更好你必须让它libav做。
所以首先我创建一个新的avframe为输出和缓冲区上的输出avframe
AVFrame * outpic = avcodec_alloc_frame（）;
nbytes = avpicture_get_size（codecCtxOut-> pix_fmt，codecCtxOut-> width，codecCtxOut-> height）;
uint8_t * outbuffer =（uint8_t *）av_malloc（nbytes）;
此缓冲区用于从输入到输出的转换。然后在循环中，我必须用缓冲区填充outpic（avframe）。
我在代码中发现这个函数用缓冲区填充平面指针。
请参阅此处
avpicture_fill（（AVPicture *）outpic，outbuffer，AV_PIX_FMT_YUV420P，codecCtxOut-> width，codecCtxOut-> height）;
然后我使用 sws_scale 。但首先您必须设置swscontext。
SwsContext * swsCtx_ = sws_getContext（codecCtxIn-> width，codecCtxIn-> height ，
codecCtxIn-> pix_fmt，
codecCtxOut-> width，codecCtxOut-> height，
codecCtxOut-> pix_fmt，
SWS_BICUBIC，NULL，NULL，
sws_scale（swsCtx_，inpic-> data，inpic-> linesize，0，codecCtxIn-> height，outpic-> data，outpic-> linesize）;然后你可以将outpic编码为pktout（用于输出的avpacket）。b。但首先要释放输出包，否则你会得到一个错误和泄漏... 请参阅这里 av_free_packet（pktOut）;
if（avcodec_encode_video2（streamOut-> codec，pktOut，outpic，& fff）< 0）{
std :: cout< shit frame<< std :: endl;
continue;
}
//并将其写入文件
formatOut-> write_packet（formatCtxOut，pktOut）;
所以现在它对我来说很好。仍然是一个小内存泄漏，但这可以后来发现。
I have some problems while trying to encode a AVFrame to a packet.
Before reading the whole code, the input stuff is working, i tested it. The output stuff is from an example here. I think there is the problem. but the segmentation fault occurs in the loop near the end.
Here is my reduced code:
void nmain() {
// input stuff
AVFormatContext *formatCtxIn=0;
AVInputFormat *formatIn=0;
AVCodecContext *codecCtxIn=0;
AVCodec *codecIn;
AVPacket *pktIn;
av_register_all();
avdevice_register_all();
avcodec_register_all();
formatIn = av_find_input_format("dshow");
if(!formatIn)
return;
AVDictionary *avoption=0;
av_dict_set(&avoption, "rtbufsize", "1000000000", NULL);
if(avformat_open_input(&formatCtxIn, "video=Integrated Camera", formatIn, &avoption)!=0)
return;
if(avformat_find_stream_info(formatCtxIn, NULL)<0)
return;
codecCtxIn = formatCtxIn->streams[0]->codec;
codecIn = avcodec_find_decoder(codecCtxIn->codec_id);
if(avcodec_open2(codecCtxIn, codecIn, NULL)<0)
return;
// end input stuff
//------------------------------------------------------------------------------
// output stuff
AVOutputFormat *formatOut=0;
AVFormatContext *formatCtxOut=0;
AVStream *streamOut=0;
AVFrame *frame=0;
AVCodec *codecOut=0;
AVPacket *pktOut;
const char *filename = "test.mpeg";
formatOut = av_guess_format(NULL, filename, NULL);
if(!formatOut)
formatOut = av_guess_format("mpeg", NULL, NULL);
if(!formatOut)
return;
formatCtxOut = avformat_alloc_context();
if(!formatCtxOut)
return;
formatCtxOut->oformat = formatOut;
sprintf(formatCtxOut->filename, "%s", filename);
if(formatOut->video_codec != AV_CODEC_ID_NONE) {
AVCodecContext *ctx;
codecOut = avcodec_find_encoder(formatOut->video_codec);
if(!codecOut)
return;
streamOut = avformat_new_stream(formatCtxOut, codecOut);
if(!streamOut)
return;
ctx = streamOut->codec;
ctx->bit_rate = 400000;
ctx->width = 352;
ctx->height = 288;
ctx->time_base.den = 25;
ctx->time_base.num = 1;
ctx->gop_size = 12;
ctx->pix_fmt = AV_PIX_FMT_YUV420P;
if(ctx->codec_id == AV_CODEC_ID_MPEG2VIDEO)
ctx->max_b_frames = 2;
if(ctx->codec_id == AV_CODEC_ID_MPEG1VIDEO)
ctx->mb_decision = 2;
if(formatCtxOut->oformat->flags & AVFMT_GLOBALHEADER)
ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
if(streamOut) {
AVCodecContext *ctx;
ctx = streamOut->codec;
if(avcodec_open2(ctx, codecOut, NULL) < 0)
return;
}
if(!(formatCtxOut->flags & AVFMT_NOFILE))
if(avio_open(&formatCtxOut->pb, filename, AVIO_FLAG_WRITE) < 0)
return;
avformat_write_header(formatCtxOut, NULL);
// doit
pktIn = new AVPacket;
pktOut = new AVPacket;
av_init_packet(pktOut);
pktOut->data = 0;
frame = avcodec_alloc_frame();
if(!frame)
return;
for(;;) {
if(av_read_frame(formatCtxIn, pktIn) >= 0) {
av_dup_packet(pktIn);
int fff;
if(avcodec_decode_video2(codecCtxIn, frame, &fff, pktIn) < 0)
std::cout << "bad frame" << std::endl;
if(!fff)
return; // ok
static int counter=0;
SaveFrame(frame, codecCtxIn->width, codecCtxIn->height, counter++); // work fine
// here a segmentation fault is occured.
if(avcodec_encode_video2(streamOut->codec, pktOut, frame, &fff) < 0)
std::cout << "bad frame" << std::endl;
}
}
}
// only for testing
// add to ensure frame is valid
void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
FILE *pFile;
char szFilename[32];
int y;
// Open file
sprintf(szFilename, "frame%d.ppm", iFrame);
pFile=fopen(szFilename, "wb");
if(pFile==NULL)
return;
// Write header
fprintf(pFile, "P6\n%d %d\n255\n", width, height);
// Write pixel data
for(y=0; y<height; y++)
fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);
// Close file
fclose(pFile);
}
What am i doing wrong?
While debugging i didn't found any problems with the parameters. streamOut->codec is filled. pktOut is allocated and frame is filled with the picture encoded before.
I think the problem is while creating the output codec but watching the example and looking to the doxypages it seems to be correct.
The trace route is from QT using msvc11 and framework 5.
I also tried to run with dr. memory and get this:
Error #26: UNADDRESSABLE ACCESS: reading 0x00000000-0x00000004 4 byte(s)
# 0 replace_memcpy [d:\derek\drmemory\withwiki\trunk\drmemory\replace.c:203]
# 1 avcodec-54.dll!ff_dct_quantize_c +0xd463 (0x6a482364 <avcodec-54.dll+0x3c2364>)
# 2 avcodec-54.dll!avcodec_encode_video2+0xb7 (0x6a56a5b8 <avcodec-54.dll+0x4aa5b8>)
# 3 nmain [d:\prg\tests\recording system-qt\libav\recsys\main.cpp:610]
# 4 main [d:\prg\tests\recording system-qt\libav\recsys\main.cpp:182]
Note: @0:00:06.318 in thread 5312
Note: instruction: mov (%edx) -> %ebx
It seems like the reading process while memcpy is going wrong.
Version:
I've forgot to mention the version of libav/ffmpeg i'm using:
libavutil 51. 76.100 / 51. 76.100
libavcodec 54. 67.100 / 54. 67.100
libavformat 54. 33.100 / 54. 33.100
libavdevice 54. 3.100 / 54. 3.100
libavfilter 3. 19.103 / 3. 19.103
libswscale 2. 1.101 / 2. 1.101
libswresample 0. 16.100 / 0. 16.100
libpostproc 52. 1.100 / 52. 1.100
Addendum:
Function SafeFrame is copied from tutorial 1.
解决方案 Finally i solved my problem.
The problem is (apart from the documentation of libav) avpacket is not a (real) copy of the picture in the packet. it just points to the data of the packet. You have to make a copy, or better you have to let it libav do.
So first i created a new avframe for the output and a buffer on which the output avframe is pointing to.
AVFrame *outpic = avcodec_alloc_frame();
nbytes = avpicture_get_size(codecCtxOut->pix_fmt, codecCtxOut->width, codecCtxOut->height);
uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes);
This buffer is used for the conversion from input to output. Then in the loop i have to fillup the outpic (avframe) with the buffer.
I have found in the code that this function is filling up the plane pointers with the buffer.
see here
avpicture_fill((AVPicture*)outpic, outbuffer, AV_PIX_FMT_YUV420P, codecCtxOut->width, codecCtxOut->height);
Then i converted the inpic to outpic using sws_scale. But first you have to setup the swscontext.
SwsContext* swsCtx_ = sws_getContext(codecCtxIn->width, codecCtxIn->height,
codecCtxIn->pix_fmt,
codecCtxOut->width, codecCtxOut->height,
codecCtxOut->pix_fmt,
SWS_BICUBIC, NULL, NULL, NULL);
sws_scale(swsCtx_, inpic->data, inpic->linesize, 0, codecCtxIn->height, outpic->data, outpic->linesize);
Then you can encode the outpic into pktout (avpacket for output). But first do free the output packet, otherwise you will get an error and a leak... see here
av_free_packet(pktOut);
if(avcodec_encode_video2(streamOut->codec, pktOut, outpic, &fff) < 0) {
std::cout << "shit frame" << std::endl;
continue;
}
// and write it to the file
formatOut->write_packet(formatCtxOut, pktOut);
So now it works (nearly fine) for me. Still a small memory leak, but this i can spot later.
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