Re-encode Audio and Video Streams

This topic describes how to use the Transcoder class to re-encode audio and video streams.

The code snippets in this article are from the re-encode sample.

Why Re-encode?

For performance reasons AVBlocks avoids re-encoding when possible, for example when you scale a video clip, the audio will be copied to the output unchanged. Another example is when you want to resample the audio part without changing the video.

However there are some cases when you will want to force re-encoding of audio or video streams, for example, to fix errors introduced by a prior encoding.

Code

To re-encode audio and video streams, configure the Transcoder outputs to be exactly the same as the inputs, and set the Param::ReEncode parameter on the output audio and the output video pins to Use::On, like this:

auto pin = primo::make_ref(Library::createMediaPin());
pin->params()->addInt(Param::ReEncode, Use::On);

Complete C++ code

bool reEncode(Options opt)
{
    wcout << L"Input file: " << opt.inputFile << endl;
    wcout << L"Output file: " << opt.outputFile << endl;
    wcout << L"Re-encode audio forced: " << opt.reEncodeAudio << endl;
    wcout << L"Re-encode video forced: " << opt.reEncodeVideo << endl;

    DeleteFile(opt.outputFile.c_str());

    auto transcoder = primo::make_ref(Library::createTranscoder());

    // In order to use the production release for testing (without a valid license), 
    // the demo mode must be enabled.
    transcoder->setAllowDemoMode(1);

    // configure input
    {
        auto mediaInfo = primo::make_ref(Library::createMediaInfo());

        mediaInfo->inputs()->at(0)->setFile(opt.inputFile.c_str());

        if (!mediaInfo->open())
        {
            printError(L"Open Info", mediaInfo->error());
            return false;
        }

        // Add Inputs
        {
            auto socket = primo::make_ref(Library::createMediaSocket(mediaInfo.get()));
            transcoder->inputs()->add(socket.get());
        }
    }

    // Add Outputs
    {
        // Add output socket
        auto socket = primo::make_ref(Library::createMediaSocket());
        socket->setStreamType(transcoder->inputs()->at(0)->streamType());
        socket->setFile(opt.outputFile.c_str());

        // Add output pins and set the ReEncode parameter to Use::On
        for (int i = 0; i < transcoder->inputs()->count(); i++)
        {
            auto inSocket = transcoder->inputs()->at(i);
            for (int j = 0; j < inSocket->pins()->count(); j++)
            {
                auto psi = primo::make_ref(inSocket->pins()->at(j)->streamInfo()->clone());

                auto pin = primo::make_ref(Library::createMediaPin());
                pin->setStreamInfo(psi.get());

                if ((MediaType::Video == psi->mediaType()) && opt.reEncodeVideo)
                {
                    pin->params()->addInt(Param::ReEncode, Use::On);
                }

                if ((MediaType::Audio == psi->mediaType()) && opt.reEncodeAudio)
                {
                    pin->params()->addInt(Param::ReEncode, Use::On);
                }

                socket->pins()->add(pin.get());
            }
        }

        transcoder->outputs()->add(socket.get());
    }

    bool_t res = transcoder->open();
    printError(L"Open Transcoder", transcoder->error());
    if (!res)
        return false;

    res = transcoder->run();
    if (!res)
        return false;

    printError(L"Run Transcoder", transcoder->error());

    transcoder->close();

    return true;
}