Hwaccel with AVCodec in FFMPEG?

Question

I am using AVCodec as a video stream decoder and would like to know if it was possible to use hardware acceleration with hwaccel via FFMPEG? or is it already used by default? I have already listed codecs available but I do not understand how to implement them in my code.

    AVHWAccel* pHwaccel = NULL;
    pHwaccel = av_hwaccel_next(NULL);

    while(pHwaccel!=NULL)
    {
        TkCore::Logger::info("%s", pHwaccel->name);
        pHwaccel = av_hwaccel_next(pHwaccel);
    }

i obtain : h264_qsv, h264_vaapi,h264_vdpaufor h264. I saw that the command : AVHWAccel * ff_find_hwaccel (codecID enum codec_id, enum PixelFormat pix_fmt) been obsolete. Thank you in advance for your help.

Answer 1

See this thread on libav-user. Basically after listing the hw accelerated codecs you can try to lookup the appropriate decoder with avcodec_find_decoder_by_name (since the AVHWAccel struct has the name field) and then use that for decoding. But then you need to know the codec upfront. If you use avformat_open_input then you may simply try to find a matching hw accelerated decoder by the codec id from the stream info, then open the hw accelerated codec by name and use that.

Update, since I got downvoted

To provide a working example of this, I have an ffmpeg installation from homebrew, that lists videotoolbox (which is a HW accelerated codec) via ffmpeg -encoders | grep h264 ffmpeg -encoders | grep h264 :

V..... h264_videotoolbox VideoToolbox H.264 Encoder (codec h264)

And the following snippet also finds it:

extern "C"
{
#include <libavcodec/avcodec.h>
}

int main(int argc, char** argv)
{
    auto *codec = avcodec_find_encoder_by_name("h264_videotoolbox");
    if (codec)
    {
        return 0;
    }
    return 1;
}

Moreover, if you check what avcodec_find_encoder_by_name / avcodec_find_encoder_by_name does, it is visible that it basically iterates the whole codec list just by applying a filter to distinguish encoders/decoders:

static AVCodec *find_codec_by_name(const char *name, int (*x)(const AVCodec *))
{
    void *i = 0;
    const AVCodec *p;

    if (!name)
        return NULL;

    while ((p = av_codec_iterate(&i))) {
        if (!x(p))
            continue;
        if (strcmp(name, p->name) == 0)
            return (AVCodec*)p;
    }

    return NULL;
}

AVCodec *avcodec_find_encoder_by_name(const char *name)
{
    return find_codec_by_name(name, av_codec_is_encoder);
}

AVCodec *avcodec_find_decoder_by_name(const char *name)
{
    return find_codec_by_name(name, av_codec_is_decoder);
}

The av_codec_iterate will iteratre the codec_list variable, which is a pregenerated list of supported codecs (populated by the features enabled when configuring the build). So if any hw accelerated codecs were enable during configuration, they will be there.

Answer 2

I realized the call of the decoder with "avcodec_find_encoder" but I do not see how to apply hardware acceleration to this decoded frame ... I have seen that pix_fmt was able to assign material acceleration, for example if pix_fmt = This is exactly as it was in h264. The only question is what function is used to apply this vdpau acceleration ...