CODEWITHSUNDEEP
ffmpegh.264libavcodeclibavnvenc
M. Ying
M. Ying

Reputation: 197

Best Settings for H264_Nvenc To Minimize Latency? (FFMPEG)

I'm currently using Libavcodec to encode video frames using H.264. Because I'm streaming this video frames after they're encoded, minimizing latency is crucial to me. My current settings are:

avcodec_register_all();
codec = avcodec_find_encoder(AV_CODEC_ID_H264);

// allocate and set ffmpeg context
context = avcodec_alloc_context3(encoder->codec);
context->bit_rate = bitrate;
context->width = out_width;
context->height = out_height;
context->time_base.num = 1;
context->time_base.den = 30;
context->gop_size = 1; // send SPS/PPS headers every packet
context->max_b_frames = 0;
context->pix_fmt = AV_PIX_FMT_YUV420P;

// set encoder parameters to max performance
av_opt_set(context->priv_data, "preset", "ultrafast", 0);
av_opt_set(context->priv_data, "tune", "zerolatency", 0);

// open capture encoder
avcodec_open2(context, codec, NULL);

These settings work well, but I am trying to switch to hardware-based encoding to take the workload off my CPU. I currently have an NVIDIA GPU, so I tried using the following settings with h264_nvenc:

codec = avcodec_find_encoder_by_name("h264_nvenc");

// allocate and set ffmpeg context
context = avcodec_alloc_context3(encoder->codec);
context->dct_algo = FF_DCT_FASTINT;
context->bit_rate = bitrate;
context->width = out_width;
context->height = out_height;
context->time_base.num = 1;
context->time_base.den = 30;
context->gop_size = 1; // send SPS/PPS headers every packet
context->max_b_frames = 0;
context->pix_fmt = AV_PIX_FMT_YUV420P;

// set encoder parameters to max performancen
av_opt_set(context->priv_data, "preset", "llhq", 0);
av_opt_set(context->priv_data, "tune", "zerolatency", 0);

The issue is, I noticed that the latency with h264_nvenc is significantly more than the latency with AV_CODEC_ID_H264 (the software-based version). I think that my settings or setup of h264_nvenc must be wrong, since GPU-based encoding should be faster than software-based encoding. Could anyone point me in the right direction? Thanks so much!

Upvotes: 2

Views: 4350

Answers (1)

puksec
puksec

Reputation: 21

av_opt_set(context->priv_data, "tune", "zerolatency", 0) worked for libx264, but when I swithed to "h264_nvenc" I had to add:

av_opt_set(m_codec_context->priv_data, "zerolatency", "1", 0);
av_opt_set(m_codec_context->priv_data, "delay", "0", 0);

Upvotes: 1

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