I learned how to use FFMPEG API with dranger's tutorial , and I implemented a video reader using the library SDL to display the video.
I have a HD video 1280*720 (i only worked with mp4) and i want to select a VGA-screen anywhere in the HD video (I mean cropping a VGA screen in a HD video), recuperate the data and display it on screen.
In the FFMPEG API, we can use the function av_picture_crop ( here ). I get a "yellow" overlay on the cropped video and my application crashes after fews seconds. Before posting here, i read here that the function wasn't finish yet. But when i reading the code, i don't find a way to finish it. This is a part of my code :
AVFrame *pFrame = NULL;
AVFrame *pFrameCropped = NULL;
bmp = SDL_CreateYUVOverlay(CODEC_WIDTH, // width
CODEC_HEIGHT, // height
SDL_YV12_OVERLAY, // format
screen); // SDL_Surface to display
sws_ctx = sws_getContext(CODEC_WIDTH, // src width
CODEC_HEIGHT, // src height
pCodecCtx->pix_fmt, // src img format
STREAM_WIDTH, // dest width,
STREAM_HEIGHT, // dest height
AV_PIX_FMT_YUV420P, // dest img format
SWS_BILINEAR, // option to rescalling
NULL, //
NULL, //
NULL //
);
while(
av_read_frame(pFormatCtx,
&packet)>=0)
{
if(packet.stream_index==videoStream)
{
avcodec_decode_video2(pCodecCtx,
pFrame,
&frameFinished,
&packet);
if(frameFinished)
{
SDL_LockYUVOverlay(bmp);
av_picture_crop((AVPicture*)pFrameCropped,
(AVPicture*)pFrame,
(AVPixelFormat)pFrame->format,
150,
300);
pict.data[0] = pFrameCropped->data[0];// "X"
pict.data[1] = pFrameCropped->data[1];
pict.data[2] = pFrameCropped->data[2];
// pict.linesize == number of bytes per line
pict.linesize[0] = pFrameCropped->linesize[0];
pict.linesize[1] = pFrameCropped->linesize[2];
pict.linesize[2] = pFrameCropped->linesize[1];
sws_scale(sws_ctx, // the scaling context previously created with sws_getContext()
(uint8_t const * const *)pFrameCropped->data, // Pointers to the planes of the source slice
pFrame->linesize, // the array containing the strides for each plane of the source image
0, // position in src img processed slice.
// It's number (counted starting from zero)
// in the image of the first row of the slice
CODEC_HEIGHT, // source slice height. Number of rows in the slice
pict.data, // pointers to the planes of the destination image
pict.linesize); // strides for each plane of the destination image
// Unlock SDL_Overlay
SDL_UnlockYUVOverlay(bmp);
}
Get the compilation error :
*** glibc detected *** ./HDtoVGA: corrupted double-linked list: 0x08d74e30 ***
In the FFMPEG command line tool, we can crop a video, using vf_crop ( here ) but I don't find how to implement the same function in my code.
Do you have any hint to help me?
Maybe the API you offered( vf_crop ) is deprecated. For the example of the latest API, you could reference filtering video example.
For cropping a video, pass value like ' crop=ow:oh:x:y
' to the variable filter_descr
:
const char *filter_descr = "crop=1/3*in_w:1/3*in_h:1/3*in_w:0";
And also, you could reference the sample project: simplest ffmpeg video filter .
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