Ffmpeg decoder yuv420p - c++

Question

I work on a video player yuv420p with ffmpeg but it's not working and i can't find out why. I spend the whole week on it...
So i have a test which just decode some frame and read it, but the output always differ, and it's really weird.
I use a video (mp4 yuv420p) which color one black pixel in more each frame :
For the video, put http://sendvid.com/b1sgf8r1 on a website like http://www.telechargerunevideo.com/en/
VideoContext is just a little struct:
struct VideoContext {
unsigned int currentFrame;
std::size_t size;
int width;
int height;
bool pause;
AVFormatContext* formatCtx;
AVCodecContext* codecCtxOrig;
AVCodecContext* codecCtx;
int streamIndex;
};
So i have a function to count the number of black pixels:
std::size_t checkFrameNb(const AVFrame* frame) {
std::size_t nb = 0;
for (int y = 0; y < frame->height; ++y) {
for (int x = 0 ; x < frame->width; ++x) {
if (frame->data[0][(y * frame->linesize[0]) + x] == BLACK_FRAME.y
&& frame->data[1][(y / 2 * frame->linesize[1]) + x / 2] == BLACK_FRAME.u
&& frame->data[2][(y / 2 * frame->linesize[2]) + x / 2] == BLACK_FRAME.v)
++nb;
}
}
return nb;
}
And this is how i decode one frame:
const AVFrame* VideoDecoder::nextFrame(entities::VideoContext& context) {
int frameFinished;
AVPacket packet;
// Allocate video frame
AVFrame* frame = av_frame_alloc();
if(frame == nullptr)
throw;
// Initialize frame->linesize
avpicture_fill((AVPicture*)frame, nullptr, AV_PIX_FMT_YUV420P, context.width, context.height);
while(av_read_frame(context.formatCtx, &packet) >= 0) {
// Is this a packet from the video stream?
if(packet.stream_index == context.streamIndex) {
// Decode video frame
avcodec_decode_video2(context.codecCtx, frame, &frameFinished, &packet);
// Did we get a video frame?
if(frameFinished) {
// Free the packet that was allocated by av_read_frame
av_free_packet(&packet);
++context.currentFrame;
return frame;
}
}
}
// Free the packet that was allocated by av_read_frame
av_free_packet(&packet);
throw core::GlobalException("nextFrame", "Frame decode failed");
}
There is already something wrong?
Maybe the context initialization will be useful:
entities::VideoContext VideoLoader::loadVideoContext(const char* file,
const int width,
const int height) {
entities::VideoContext context;
// Register all formats and codecs
av_register_all();
context.formatCtx = avformat_alloc_context();
// Open video file
if(avformat_open_input(&context.formatCtx, file, nullptr, 0) != 0)
throw; // Couldn't open file
// Retrieve stream information
if(avformat_find_stream_info(context.formatCtx, nullptr) > 0)
throw; // Couldn't find stream information
// Dump information about file onto standard error
//av_dump_format(m_formatCtx, 0, file, 1);
// Find the first video stream because we don't need more
for(unsigned int i = 0; i < context.formatCtx->nb_streams; ++i)
if(context.formatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
context.streamIndex = i;
context.codecCtx = context.formatCtx->streams[i]->codec;
break;
}
if(context.codecCtx == nullptr)
throw; // Didn't find a video stream
// Find the decoder for the video stream
AVCodec* codec = avcodec_find_decoder(context.codecCtx->codec_id);
if(codec == nullptr)
throw; // Codec not found
// Copy context
if ((context.codecCtxOrig = avcodec_alloc_context3(codec)) == nullptr)
throw;
if(avcodec_copy_context(context.codecCtxOrig, context.codecCtx) != 0)
throw; // Error copying codec context
// Open codec
if(avcodec_open2(context.codecCtx, codec, nullptr) < 0)
throw; // Could not open codec
context.currentFrame = 0;
decoder::VideoDecoder::setVideoSize(context);
context.pause = false;
context.width = width;
context.height = height;
return std::move(context);
}
I know it's not a little piece of code, if you have any idea too make an exemple more brief, go on.
And if someone have an idea about this issue, there is my output:
9 - 10 - 12 - 4 - 10 - 14 - 11 - 8 - 9 - 10
But i want :
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10
PS:
get fps and video size are copy paste code of opencv