c++ videoplayer ffmpeg: get pixel data? - c++

Question

I want to get the pixel data of a frame. I found this (in original version as old code) and changed some things.
I have this code:
AVFormatContext *pFormatCtx;
pFormatCtx = avformat_alloc_context();
// Open file
if (int err = avformat_open_input(&pFormatCtx, file, NULL, 0) != 0)
{
exit(2);
}
// Get infromation about streams
if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
{
exit(2);
}
// # video stream
int videoStreamIndex = -1;
AVCodecContext *pVideoCodecCtx;
AVCodec *pVideoCodec;
int res = 0;
int width = 0;
int height = 0;
for (unsigned int i = 0; i < pFormatCtx->nb_streams; i++)
{
if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
videoStreamIndex = i;
pVideoCodecCtx = pFormatCtx->streams[i]->codec;
// Find decoder
pVideoCodec = avcodec_find_decoder(pVideoCodecCtx->codec_id);
if (pVideoCodec)
{
// Open decoder
res = !(avcodec_open2(pVideoCodecCtx, pVideoCodec, NULL) < 0);
width = pVideoCodecCtx->coded_width;
height = pVideoCodecCtx->coded_height;
}
break;
}
}
// Frame width
width = pFormatCtx->streams[videoStreamIndex]->codec->width;
// Frame height
height = pFormatCtx->streams[videoStreamIndex]->codec->height;
AVPacket packet;
int got_picture_ptr;
AVPacket *avpkt;
AVFrame * pOutFrame;
pOutFrame = av_frame_alloc();
AVFrame * rgbOutFrame = av_frame_alloc();
if (!pOutFrame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
while (av_read_frame(pFormatCtx, &packet) >= 0)
{
if (packet.stream_index == videoStreamIndex)
{
// Decode packeg to frame.
int videoFrameBytes = avcodec_decode_video2(pVideoCodecCtx, pOutFrame,
&got_picture_ptr, &packet);
// Create context
SwsContext* pImgConvertCtx = sws_getContext(pVideoCodecCtx->width,
pVideoCodecCtx->height,
pVideoCodecCtx->pix_fmt,
pVideoCodecCtx->width, pVideoCodecCtx->height,
AV_PIX_FMT_YUV420P,
SWS_BICUBIC, NULL, NULL, NULL);
// Convert frame
sws_scale(pImgConvertCtx, pOutFrame->data, pOutFrame->linesize,
width, height, rgbOutFrame->data, rgbOutFrame->linesize);
}
}
I know, that the code from SwsContext and sws_scale is wrong but I wonder, where can I find the pixel data of my frame... (and in which format it is stored).
Can someone help me here?

Answer 1

Pixel data is stored in data field.
According to the documentation:
uint8_t* AVFrame::data[AV_NUM_DATA_POINTERS]
pointer to the picture/channel planes.
Look here for more information.
Generally speaking, your code is a bit misleading and rather buggy. I can point out some drawbacks:
1) You don't need to create new SwsContext on every incoming video packet. Just create it once before while cycle.
2) Next, you have an rgbOutFrame, but SwsContext is created for scaling into the YUV420 pixel format. It looks strange.
3) Besides, avcodec_decode_video2 is invoked, but you never check neither return value nor got_picture_ptr flag. Such practice is really error-prone.
And so on...
Hope it'll help you to improve your program and get necessary results.