How to new & delete AVPacket? - c++

Question

I'm working with a FFmpeg project right now, I have to store the data of AVPacket which from av_read_frame, and fill data to new AVPacket for following decoding.
Here is my problem: when I try to new & free an AVPacket, memory leaks always happen.
I am just doing a simple testing:
for(;;) {
AVPacket pkt;
av_new_packet(&pkt, 1000);
av_init_packet(&pkt);
av_free_packet(&pkt);
}
What am I doing wrong?

Answer 1

av_new_packet creates a packet and allocates data
av_init_packet
sets all packet members to default, and sets data pointer to NULL,
the leak is here
av_free_packet clears all visible members, but
your data is already leaking
If you want FFmpeg to allocate the data for you, do not call av_init_packet. If you want to handle the data yourself, allocate the packet object on the stack and set its data yourself (and free it yourself):
AVPacket pkt;
av_init_packet(&pkt);
pkt.data = dataBuffer;
pkt.size = dataBufferSize;
// use your packet
// free your dataBuffer

Answer 2

I just read the FFmpeg 2.2 AVPacket.c source code.
int av_new_packet(AVPacket *pkt, int size) {
AVBufferRef *buf = NULL;
int ret = packet_alloc(&buf, size);
if (ret < 0)
return ret;
av_init_packet(pkt);
pkt->buf = buf;
pkt->data = buf->data;
pkt->size = size;
#if FF_API_DESTRUCT_PACKET
FF_DISABLE_DEPRECATION_WARNINGS
pkt->destruct = dummy_destruct_packet;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
return 0;
}
void av_init_packet(AVPacket *pkt) {
pkt->pts = AV_NOPTS_VALUE;
pkt->dts = AV_NOPTS_VALUE;
pkt->pos = -1;
pkt->duration = 0;
pkt->convergence_duration = 0;
pkt->flags = 0;
pkt->stream_index = 0;
#if FF_API_DESTRUCT_PACKET
FF_DISABLE_DEPRECATION_WARNINGS
pkt->destruct = NULL;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
pkt->buf = NULL;
pkt->side_data = NULL;
pkt->side_data_elems = 0;
}
I don't really know about the defines FF_API_DESTRUCT_PACKET, FF_DISABLE_DEPRECATION_WARNINGS, FF_ENABLE_DEPRECATION_WARNINGS
Some reason makes destruct of av_free_packet leak
According the source code, av_init_packet is called in av_new_packet and av_new_packet already allocates the AVBuffer, so if you want to set the data to new AVPacket.
Just memory copy to data of AVPacket, and call av_free_packet when you are done.