Failing to properly initialize AVFrame for sws_scale conversion

Question

I'm decoding video using FFMpeg, and want to edit the decoded frames using OpenGL, but in order to do that I need to convert the data in AVFrame from YUV to RGB.

In order to do that I create a new AVFrame:

AVFrame *inputFrame = av_frame_alloc();
AVFrame *outputFrame = av_frame_alloc();
av_image_alloc(outputFrame->data, outputFrame->linesize, width, height, AV_PIX_FMT_RGB24, 1);
av_image_fill_arrays(outputFrame->data, outputFrame->linesize, NULL, AV_PIX_FMT_RGB24, width, height, 1);

Create a conversion context:

struct SwsContext *img_convert_ctx = sws_getContext(width, height, AV_PIX_FMT_YUV420P,
                                                  width, height, AV_PIX_FMT_RGB24,
                                                  0, NULL, NULL, NULL);

And then try to convert it to RGB:

sws_scale(img_convert_ctx, (const uint8_t *const *)&inputFrame->data, inputFrame->linesize, 0, inputFrame->height, outputFrame->data, outputFrame->linesize);

But this causes an "[swscaler @ 0x123f15000] bad dst image pointers" error during run time. When I went over FFMpeg's source I found out that the reason is that outputFrame's data wasn't initialized, but I don't understand how it should be.

All existing answers or tutorials that I found (see example) seem to use deprecated APIs, and it's unclear how to use the new APIs. I'd appreciate any help.

Answer 1

Here's how I call sws_scale:

image buf2((buf.w + 15)/16*16, buf.h, 3);
sws_scale(sws_ctx, (const uint8_t * const *)frame->data, frame->linesize, 0, c->height, (uint8_t * const *)buf2.c, &buf2.ys);

There are two differences here:

1. You pass &inputFrame->data but it shall be inputFrame->data without the address-of operator.

2. You don't have to allocate a second frame structure. The sws_scale doesn't care about it. It just needs a chunk of memory of the proper size (and maybe alignment).