如何新建和删除 AVPacket？

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.