Fast way of opening Live Input with libavcodec

Question

I'm currently working with a live video input from the Hauppauge WinTV950Q, which gives me a live Video Input.

I'm using the libav* and Qt library and am programming in C/C++ on Linux. I use the recommended avcodec_open_input() for opening and processing (transcoding) the input for the use on mobile Devices. I want to be able to watch TV on my mobile Devices and also be able to switch channels remotely. Everything works fine so far.

My only problem is that the opening of an input takes between 5 and 20 seconds. Which is to slow for my use case, I would be okay with delays between 1-3 seconds. The v4l2-API which I formerly used for first tests actually manages to get switch times between 1-3seconds, I can not use it though because I need to do some transcoding so I can use the video data on my mobile devices.

Is there a way to improve the opening time of the avformat_open_input() call? Maybe some global variables in the library that need to be set before opening the input?

Here's the relevant piece of code:

const char* filename = "/dev/dvb/adapter0/dvr0";

int main(void)
{
    /*Qt-Variables*/
    QTime timer;
    /*General AV-IO*/
    int i, videoStream, audioStream, frameFinished;
    AVFormatContext *ptrFormatContext;
    AVPacket ptrPacket;
    /*Audio related*/
    AVCodecContext  *aCodecCtx;
    AVCodecContext  *aTargetCodecCtxt;
    AVCodec         *aCodec;
    AVCodec         *aTargetCodec;
    uint8_t         *audio_samples;
    int             frame_size_ptr;
    //    AVSampleFormat  ptrSampleFormats[2] = {AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_S32};

    /*Video related*/
    AVCodecContext *ptrCodecCtxt;
    AVCodecContext  *vTargetCodecCtxt;
    AVCodec *ptrCodec;
    AVCodec         *vTargetCodec;
    AVFrame *ptrFrame;

    /*Default Initialization of Variables*/
    audioStream = videoStream = -1;
    audio_samples = NULL;


    /*Registering and initialization of the libav* codecs, formats, filter etc.*/

    qDebug("Registering Codecs, Filter, Formats, Media Libraries etc...");
    timer.start();
    av_register_all();
    avcodec_register_all();
    qDebug()<<"Elapsed(ms): "<<timer.elapsed();

    /*Assigning a memory array to the Format Context and the Frame for the Video decoding, now we can start working*/
    qDebug("Allocating Codec Context and Frames for main Input...");
    timer.start();
    ptrFrame = avcodec_alloc_frame();
    ptrFormatContext = avformat_alloc_context();
    qDebug()<<"Elapsed(ms): "<<timer.elapsed();

    /*Opening the Live Video Input, sometimes very slow.*/
    qDebug("Trying to open the Input...");
    timer.start();
    if(avformat_open_input(&ptrFormatContext, filename, NULL, NULL) != 0 )
    {
        qDebug("Error opening the input");
        exit(-1);
    } else qDebug()<<"Elapsed(ms): "<<timer.elapsed();

Here's the output:

Registering Codecs, Filter, Formats, Media Libraries etc...
Elapsed(ms):  0 
Allocating Codec Context and Frames for main Input...
Elapsed(ms):  0 
Trying to open the Input...
Elapsed(ms):  14752 

Answer 1

Not sure if this will help you, I am quite a libavcodec n00b :)

Try setting max_analyze_duration on the ptrFormatContext to a low value...

I have successfully used this to speed up opening of live mjpeg streams