如何使用FFMPEG从存储为视频AVPackets的NAL单元播放H.264流

Question

I am writing client-server system that uses FFMPEG library to parse H.264 stream into NAL units on the server side, then uses channel coding to send them over network to client side, where my application must be able to play video.

The question is how to play received AVPackets (NAL units) in my application as video stream. I have found this tutorial helpful and used it as base for both server and client side.

Some sample code or resource related to playing video not from file, but from data inside program using FFMPEG library would be very helpful.

I am sure that received information will be sufficient to play video, because I tried to save received data as .h264 or .mp4 file and it can be played by VLC player.

Answer 1

Of what I understand from your question, you have the AVPackets and want to play a video. In reality this is two problems; 1. decoding your packets, and 2. playing the video.

For decoding your packets, with FFmpeg, you should take a look at the documentation for AVPacket , AVCodecContext and avcodec_decode_video2 to get some ideas; the general idea is that you want to do something (just wrote this in the browser, take with a grain of salt) along the lines of:

//the context, set this appropriately based on your video. See the above links for the documentation 
AVCodecContext *decoder_context; 
std::vector<AVPacket> packets;   //assume this has your packets
...
AVFrame *decoded_frame = av_frame_alloc();
int ret = -1;
int got_frame = 0;
for(AVPacket packet : packets) 
{
    avcodec_get_frame_defaults(frame);
    ret = avcodec_decode_video2(decoder_context, decoded_frame, &got_frame, &packet);
    if (ret <= 0) {
        //had an error decoding the current packet or couldn't decode the packet
        break;
    } 

    if(got_frame)
    {
        //send to whatever video player queue you're using/do whatever with the frame
        ...
    }
    got_frame = 0;
    av_free_packet(&packet);
}

It's a pretty rough sketch, but that's the general idea for your problem of decoding the AVPackets. As for your problem of playing the video, you have many options, which will likely depend more on your clients. What you're asking is a pretty large problem, I'd advise familiarizing yourself with the FFmpeg documentation and the provided examples at the FFmpeg site . Hope that makes sense