How to change the settings of AVCodecContext after initialization (FFMPEG) - ffmpeg

Question

I have a question about Libavcodec that I can't find the answer to online. I'm trying to use H.264 to encode frames. The issue I'm having is that the frames I wish to encode have variable widths and heights. I understand that to encode frames in Libavcodec, you need to pass a "width" and "height" parameter to the AvCodecContext struct, and then initialize it as such:
AVCodec *codec = codec = avcodec_find_encoder(AV_CODEC_ID_H264);
AVCodecContext *context = avcodec_alloc_context3(encoder->codec);
context->width = 1920;
//OTHER SETTINGS HERE
//FINALLY...
avcodec_open2(context, codec, NULL);
Let's say that, after I've initialized this context, I need to encode a different frame that now has a width of 900. I can't simply just do context->width = 900 because the context has already been set to width 1920 and initialized. I could create an entirely new AvCodecContext and delete the previous one with avcodec_close() as follows:
AVCodec *codec = codec = avcodec_find_encoder(AV_CODEC_ID_H264);
AVCodecContext *context = avcodec_alloc_context3(encoder->codec);
context->width = 900;
//OTHER SETTINGS HERE
//FINALLY...
avcodec_open2(context, codec, NULL);
// DO THE ENCODING HERE
avcodec_close(context);
But my program has been crashing unexpectedly when I do this, and I feel like recreating the AVCodecContext every time I need to change a simple width/height setting is inefficient to begin with. Does anyone have any suggestions as to how I can go about doing this? Thank you very much!

Answer 1

That’s not a thing. You must reinitialize the encoder, or scale/pad the frames to the same size

Answer 2

I had the same problem, I solved it like this:
First I changed the codecContext width and height (They should be even numbers):
while (w%2 != 0) {
w--;
}
while (h%2 != 0) {
h--;
}
cctx->bit_rate = w*h*10;
cctx->width = w;
cctx->height = h;
Secons I initialized the codec with changed codecContext:
codec->init(cctx);
And finally destroy and recreated the AVFrame (I couldn't find a method to reinitialize frame without recreation and simply changing width and height doesn't work):
if (videoFrame) {
av_frame_free(&videoFrame);
}
if (!videoFrame) {
videoFrame = av_frame_alloc();
videoFrame->format = AV_PIX_FMT_YUV420P;
videoFrame->width = cctx->width;
videoFrame->height = cctx->height;
if ((av_frame_get_buffer(videoFrame, 32)) < 0) {
std::cout << "Failed to allocate picture" << std::endl;
return;
}
}