FFMPEG: Can not free AVPacket when decode H264 stream? - c++

Question

I'm using FFMPEG to decode H264 stream, my code is below
AVFormatContext *pFormatCtx = NULL;
AVCodecContext *pCodecCtx = NULL;
AVFrame *pFrame = NULL;
AVPacket packet;
packet.data = NULL;
pFormatCtx = avformat_alloc_context();
avformat_open_input(&pFormatCtx, videoStreamPath, NULL, NULL);
liveHeader.pCodecCtx = pFormatCtx->streams[videoStreamIndex]->codec;
int bytesDecoded = 0;
int frameFinished = 0;
while (true)
{
while (packet.size > 0)
{
// Decode the next chunk of data
bytesDecoded = avcodec_decode_video2(pCodecCtx, pFrame,
&frameFinished, &packet);
// Was there an error?
if (bytesDecoded < 0)
{
printf(strErr, "Error while decoding frame\n");
commonGlobal->WriteRuntimeRecLogs(strErr);
return RS_NOT_OK;
}
packet.size -= bytesDecoded;
packet.data += bytesDecoded;
if (frameFinished)
{
//av_free_packet(&packet); //(free 1)
return RS_OK;
}
// Did we finish the current frame? Then we can return
}
do
{
try
{
int ret = av_read_frame(pFormatCtx, &packet);
if (ret < 0)
{
char strErr[STR_LENGTH_256];
if (ret == AVERROR_EOF || (pFormatCtx->pb && pFormatCtx->pb->eof_reached))
{
sprintf(strErr, "Error end of file line %d", __LINE__);
}
if (pFormatCtx->pb && pFormatCtx->pb->error)
{
sprintf(strErr, "Error end of file line %d", __LINE__);
}
packet.data = NULL;
return RS_NOT_OK;
}
}
catch (...)
{
packet.data = NULL;
return RS_NOT_OK;
}
} while (packet.stream_index != videoStreamIndex);
}
//av_free_packet(&packet); //(free 2)
The problem is I don't know how to free memory of packet correctly.
I have tried to delete packet's data by calling one of two places av_free_packet(&packet); (free 1) and av_free_packet(&packet); (free 2). And the result is the application was crashed with the message "Heap Corruption..."
If I do not free the packet, the memory leak is occur.
Note that the above code is successful when decode H264 stream, the main problem is memory leak and crashed when I try to free the packet
Someone can show me the problems in my code.
Many thanks,
T&T

Answer 1

av_free_packet will clear your packet data, the same pointer that was allocated inside av_read_frame. But you changed it in packet.data += bytesDecoded; => crash.
Several advices:
No need to call av_init_packet if the first use of your packet is av_read_frame (it is done inside this function). But if you keep your code, you need it in order to initialize packet.size to 0 (tested, but not initialized the first time)
Call av_free_packet each time you are done with the packet data, only when the decode is successful. In your code, it means you must call it after avcodec_decode_video2, even if the frame is not finished.
Once your packed is decoded (i.e. avcodec_decode_video2 is ok, no matter if frameFinished is true or false), you can free it. No need to keep it and change data pointer. The process is "read packet, decode it, free it. read next packet, decode it, free it.". (Note that this does not apply to audio packets).
I suggest simplify your main loop by something like (read first, decode after):
while(true)
{
// Step 1: Read packet
while(true)
{
av_read_frame(pFormatCtx, &packet);
// todo: Error handling
if(packet.stream_index != videoStreamIndex)
{
av_free_packet(&packet);
}
else
{
break;
}
} while (packet.stream_index != videoStreamIndex);
// Step 2/3: Decode and free
avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
av_free_packet(&packet);
// todo: Error handling and checking frameFinished if needed
// Of course, if you need to use the packet now, move the av_free_packet() after this
}

Answer 2

You should initialize your packet before usage as following:
AVPacket packet;
av_init_packet(&packet);
Also your not deleting your AVFormatContext instance.
avformat_free_context(pFormatCtx);