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.

Rudolfs Bundulis · Answer 1 · 2020-01-06T08:18:40.563

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:

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.

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 ... — HellBlood, Apr 15 '19 at 07:52
As I said in my response - if you open the hw accelerated codec by name, you already have a codec instance with the hardware acceleration enabled. The point of the hw accelerated codecs is that they will always use the hardware acceleration, while the standard ones will not. Thus, all you have to do is properly open it and use it in your pipeline. — Rudolfs Bundulis, Apr 15 '19 at 09:04
avcodec_find_decoder_by_name cannot find AVHWAccel. only can find register decoder. — tbago, Jan 03 '20 at 02:31
@tbago did you actually verify that or just comment and downvote? I can find `h264_videotoolbox` just fine, expanded the answer with a simple snippet. — Rudolfs Bundulis, Jan 06 '20 at 08:14
https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/hw_decode.c.You can see this demo show how to use hardware decoder. — tbago, Jan 08 '20 at 01:03

score 0 · Answer 2 · answered Apr 15 '19 at 07:53

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 ...

Hwaccel with AVCodec in FFMPEG?

2 Answers2