FFmpeg C++ api decode h264 error - c++

Question

I'm trying to use the C++ API of FFMpeg (version 20150526) under Windows using the prebuilt binaries to decode an h264 video file (*.ts).
I've written a very simple code that automatically detects the required codec from the file itself (and it is AV_CODEC_ID_H264, as expected).
Then I re-open the video file in read-binary mode and I read a fixed-size buffer of bytes from it and provide the read bytes to the decoder within a while-loop until the end of file. However when I call the function avcodec_decode_video2 a large amount of errors happen like the following ones:
[h264 # 008df020] top block unavailable for requested intro mode at 34 0
[h264 # 008df020] error while decoding MB 34 0, bytestream 3152
[h264 # 008df020] decode_slice_header error
Sometimes the function avcodec_decode_video2 sets the value of got_picture_ptr to 1 and hence I expect to find a good frame. Instead, though all the computations are successful, when I view the decoded frame (using OpenCV only for visualization purposes) I see a gray one with some artifacts.
If I employ the same code to decode an *.avi file it works fine.
Reading the examples of FFMpeg I did not find a solution to my problem. I've also implemented the solution proposed in the simlar question FFmpeg c++ H264 decoding error but it did not work.
Does anyone know where the error is?
Thank you in advance for any reply!
The code is the following [EDIT: code updated including the parser management]:
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <opencv2/opencv.hpp>
#ifdef __cplusplus
extern "C"
{
#endif // __cplusplus
#include <libavcodec/avcodec.h>
#include <libavdevice/avdevice.h>
#include <libavfilter/avfilter.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libavutil/avutil.h>
#include <libpostproc/postprocess.h>
#include <libswresample/swresample.h>
#include <libswscale/swscale.h>
#ifdef __cplusplus
} // end extern "C".
#endif // __cplusplus
#define INBUF_SIZE 4096
void main()
{
AVCodec* l_pCodec;
AVCodecContext* l_pAVCodecContext;
SwsContext* l_pSWSContext;
AVFormatContext* l_pAVFormatContext;
AVFrame* l_pAVFrame;
AVFrame* l_pAVFrameBGR;
AVPacket l_AVPacket;
AVPacket l_AVPacket_out;
AVStream* l_pStream;
AVCodecParserContext* l_pParser;
FILE* l_pFile_in;
FILE* l_pFile_out;
std::string l_sFile;
int l_iResult;
int l_iFrameCount;
int l_iGotFrame;
int l_iBufLength;
int l_iParsedBytes;
int l_iPts;
int l_iDts;
int l_iPos;
int l_iSize;
int l_iDecodedBytes;
uint8_t l_auiInBuf[INBUF_SIZE + FF_INPUT_BUFFER_PADDING_SIZE];
uint8_t* l_pData;
cv::Mat l_cvmImage;
l_pCodec = NULL;
l_pAVCodecContext = NULL;
l_pSWSContext = NULL;
l_pAVFormatContext = NULL;
l_pAVFrame = NULL;
l_pAVFrameBGR = NULL;
l_pParser = NULL;
l_pStream = NULL;
l_pFile_in = NULL;
l_pFile_out = NULL;
l_iPts = 0;
l_iDts = 0;
l_iPos = 0;
l_pData = NULL;
l_sFile = "myvideo.ts";
avdevice_register_all();
avfilter_register_all();
avcodec_register_all();
av_register_all();
avformat_network_init();
l_pAVFormatContext = avformat_alloc_context();
l_iResult = avformat_open_input(&l_pAVFormatContext,
l_sFile.c_str(),
NULL,
NULL);
if (l_iResult >= 0)
{
l_iResult = avformat_find_stream_info(l_pAVFormatContext, NULL);
if (l_iResult >= 0)
{
for (int i=0; i<l_pAVFormatContext->nb_streams; i++)
{
if (l_pAVFormatContext->streams[i]->codec->codec_type ==
AVMEDIA_TYPE_VIDEO)
{
l_pCodec = avcodec_find_decoder(
l_pAVFormatContext->streams[i]->codec->codec_id);
l_pStream = l_pAVFormatContext->streams[i];
}
}
}
}
av_init_packet(&l_AVPacket);
av_init_packet(&l_AVPacket_out);
memset(l_auiInBuf + INBUF_SIZE, 0, FF_INPUT_BUFFER_PADDING_SIZE);
if (l_pCodec)
{
l_pAVCodecContext = avcodec_alloc_context3(l_pCodec);
l_pParser = av_parser_init(l_pAVCodecContext->codec_id);
if (l_pParser)
{
av_register_codec_parser(l_pParser->parser);
}
if (l_pAVCodecContext)
{
if (l_pCodec->capabilities & CODEC_CAP_TRUNCATED)
{
l_pAVCodecContext->flags |= CODEC_FLAG_TRUNCATED;
}
l_iResult = avcodec_open2(l_pAVCodecContext, l_pCodec, NULL);
if (l_iResult >= 0)
{
l_pFile_in = fopen(l_sFile.c_str(), "rb");
if (l_pFile_in)
{
l_pAVFrame = av_frame_alloc();
l_pAVFrameBGR = av_frame_alloc();
if (l_pAVFrame)
{
l_iFrameCount = 0;
avcodec_get_frame_defaults(l_pAVFrame);
while (1)
{
l_iBufLength = fread(l_auiInBuf,
1,
INBUF_SIZE,
l_pFile_in);
if (l_iBufLength == 0)
{
break;
}
else
{
l_pData = l_auiInBuf;
l_iSize = l_iBufLength;
while (l_iSize > 0)
{
if (l_pParser)
{
l_iParsedBytes = av_parser_parse2(
l_pParser,
l_pAVCodecContext,
&l_AVPacket_out.data,
&l_AVPacket_out.size,
l_pData,
l_iSize,
l_AVPacket.pts,
l_AVPacket.dts,
AV_NOPTS_VALUE);
if (l_iParsedBytes <= 0)
{
break;
}
l_AVPacket.pts = l_AVPacket.dts = AV_NOPTS_VALUE;
l_AVPacket.pos = -1;
}
else
{
l_AVPacket_out.data = l_pData;
l_AVPacket_out.size = l_iSize;
}
l_iDecodedBytes =
avcodec_decode_video2(
l_pAVCodecContext,
l_pAVFrame,
&l_iGotFrame,
&l_AVPacket_out);
if (l_iDecodedBytes >= 0)
{
if (l_iGotFrame)
{
l_pSWSContext = sws_getContext(
l_pAVCodecContext->width,
l_pAVCodecContext->height,
l_pAVCodecContext->pix_fmt,
l_pAVCodecContext->width,
l_pAVCodecContext->height,
AV_PIX_FMT_BGR24,
SWS_BICUBIC,
NULL,
NULL,
NULL);
if (l_pSWSContext)
{
l_iResult = avpicture_alloc(
reinterpret_cast<AVPicture*>(l_pAVFrameBGR),
AV_PIX_FMT_BGR24,
l_pAVFrame->width,
l_pAVFrame->height);
l_iResult = sws_scale(
l_pSWSContext,
l_pAVFrame->data,
l_pAVFrame->linesize,
0,
l_pAVCodecContext->height,
l_pAVFrameBGR->data,
l_pAVFrameBGR->linesize);
if (l_iResult > 0)
{
l_cvmImage = cv::Mat(
l_pAVFrame->height,
l_pAVFrame->width,
CV_8UC3,
l_pAVFrameBGR->data[0],
l_pAVFrameBGR->linesize[0]);
if (l_cvmImage.empty() == false)
{
cv::imshow("image", l_cvmImage);
cv::waitKey(10);
}
}
}
l_iFrameCount++;
}
}
else
{
break;
}
l_pData += l_iParsedBytes;
l_iSize -= l_iParsedBytes;
}
}
} // end while(1).
}
fclose(l_pFile_in);
}
}
}
}
}
EDIT: The following is the final code that solves my problem, thanks to the suggestions of Ronald.
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <opencv2/opencv.hpp>
#ifdef __cplusplus
extern "C"
{
#endif // __cplusplus
#include <libavcodec/avcodec.h>
#include <libavdevice/avdevice.h>
#include <libavfilter/avfilter.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libavutil/avutil.h>
#include <libpostproc/postprocess.h>
#include <libswresample/swresample.h>
#include <libswscale/swscale.h>
#ifdef __cplusplus
} // end extern "C".
#endif // __cplusplus
void main()
{
AVCodec* l_pCodec;
AVCodecContext* l_pAVCodecContext;
SwsContext* l_pSWSContext;
AVFormatContext* l_pAVFormatContext;
AVFrame* l_pAVFrame;
AVFrame* l_pAVFrameBGR;
AVPacket l_AVPacket;
std::string l_sFile;
uint8_t* l_puiBuffer;
int l_iResult;
int l_iFrameCount;
int l_iGotFrame;
int l_iDecodedBytes;
int l_iVideoStreamIdx;
int l_iNumBytes;
cv::Mat l_cvmImage;
l_pCodec = NULL;
l_pAVCodecContext = NULL;
l_pSWSContext = NULL;
l_pAVFormatContext = NULL;
l_pAVFrame = NULL;
l_pAVFrameBGR = NULL;
l_puiBuffer = NULL;
l_sFile = "myvideo.ts";
av_register_all();
l_iResult = avformat_open_input(&l_pAVFormatContext,
l_sFile.c_str(),
NULL,
NULL);
if (l_iResult >= 0)
{
l_iResult = avformat_find_stream_info(l_pAVFormatContext, NULL);
if (l_iResult >= 0)
{
for (int i=0; i<l_pAVFormatContext->nb_streams; i++)
{
if (l_pAVFormatContext->streams[i]->codec->codec_type ==
AVMEDIA_TYPE_VIDEO)
{
l_iVideoStreamIdx = i;
l_pAVCodecContext =
l_pAVFormatContext->streams[l_iVideoStreamIdx]->codec;
if (l_pAVCodecContext)
{
l_pCodec = avcodec_find_decoder(l_pAVCodecContext->codec_id);
}
break;
}
}
}
}
if (l_pCodec && l_pAVCodecContext)
{
l_iResult = avcodec_open2(l_pAVCodecContext, l_pCodec, NULL);
if (l_iResult >= 0)
{
l_pAVFrame = av_frame_alloc();
l_pAVFrameBGR = av_frame_alloc();
l_iNumBytes = avpicture_get_size(PIX_FMT_BGR24,
l_pAVCodecContext->width,
l_pAVCodecContext->height);
l_puiBuffer = (uint8_t *)av_malloc(l_iNumBytes*sizeof(uint8_t));
avpicture_fill((AVPicture *)l_pAVFrameBGR,
l_puiBuffer,
PIX_FMT_RGB24,
l_pAVCodecContext->width,
l_pAVCodecContext->height);
l_pSWSContext = sws_getContext(
l_pAVCodecContext->width,
l_pAVCodecContext->height,
l_pAVCodecContext->pix_fmt,
l_pAVCodecContext->width,
l_pAVCodecContext->height,
AV_PIX_FMT_BGR24,
SWS_BICUBIC,
NULL,
NULL,
NULL);
while (av_read_frame(l_pAVFormatContext, &l_AVPacket) >= 0)
{
if (l_AVPacket.stream_index == l_iVideoStreamIdx)
{
l_iDecodedBytes = avcodec_decode_video2(
l_pAVCodecContext,
l_pAVFrame,
&l_iGotFrame,
&l_AVPacket);
if (l_iGotFrame)
{
if (l_pSWSContext)
{
l_iResult = sws_scale(
l_pSWSContext,
l_pAVFrame->data,
l_pAVFrame->linesize,
0,
l_pAVCodecContext->height,
l_pAVFrameBGR->data,
l_pAVFrameBGR->linesize);
if (l_iResult > 0)
{
l_cvmImage = cv::Mat(
l_pAVFrame->height,
l_pAVFrame->width,
CV_8UC3,
l_pAVFrameBGR->data[0],
l_pAVFrameBGR->linesize[0]);
if (l_cvmImage.empty() == false)
{
cv::imshow("image", l_cvmImage);
cv::waitKey(1);
}
}
}
l_iFrameCount++;
}
}
}
}
}
}

Answer 1

You're never using the l_pParser object, or in other words, you're not using a H264 parser, you're just sending raw file data into the decoder without proper NAL packetization. Please read the frame parsing API docs to figure out how to use the parser.