How to encode h.264 with libavcodec/x264?

Question

I am attempting to encode video using libavcodec/libavformat. Audio works great, but when I try to encode video I get the following errors:

[libx264 @ 0x10182a000]broken ffmpeg default settings detected   [libx264 @ 0x10182a000]use an encoding preset (vpre)   

easy to fix using the command line ffmpeg, but I am trying to do this in C. my options are

AVStream *pVideoOutStream = av_new_stream(pOutFormatCtx, 0);   AVCodecContext *pVideoOutCodecCtx  = pVideoOutStream->codec;    pVideoOutCodecCtx->codec_id        = CODEC_ID_H264;     pVideoOutCodecCtx->codec_type      = CODEC_TYPE_VIDEO;   pVideoOutCodecCtx->bit_rate        = pVideoInCodecCtx->bit_rate;   pVideoOutCodecCtx->width           = pVideoInCodecCtx->width;     pVideoOutCodecCtx->height          = pVideoInCodecCtx->height;   pVideoOutCodecCtx->pix_fmt         = pVideoInCodecCtx->pix_fmt;     pVideoOutCodecCtx->sample_rate     = pVideoInCodecCtx->sample_rate;     pVideoOutCodecCtx->gop_size        = 30;   

but avcodec_open() fails.

What other values do I need to set to make x264 happy?

Answer 1

Don't forget to use x264 private options. You can always set a profile:

av_dict_set(&This->opts, "vprofile", "baseline", 0) 

Or set the lowest encoding latency:

av_dict_set(&This->opts, "tune", "zerolatency", 0); 

Or select a preset:

av_dict_set(&This->opts, "preset","ultrafast",0); 

Before opening a codec

avcodec_open2(This->context, This->codec, &This->opts) 

Answer 2

The following is how to interpret the ffmpeg's x264 presets.

Unfortunately I don't know of an easy way to import the presets like ffmpeg does. You can lookup the x264 preset values which are all stored in /usr/local/share/ffmpeg/libx264-{name}.ffpreset, where {name} is specified for ffmpeg as the -vpre {name} command-line argument. So typically ffmpeg would include libx264-medium.ffpreset and then libx264-main.ffpreset, specified as ffmpeg -vpre medium -vpre main

You can lookup all the options (as defined in the libx264-{name}.ffpreset files) to get their structure names by looking in the libavcodec/options.c file, which can be found in the ffmpeg SVN repositories.

Here's how the medium and main presets would be translated into C code:

// libx264-medium.ffpreset preset ctx->coder_type = 1;  // coder = 1 ctx->flags|=CODEC_FLAG_LOOP_FILTER;   // flags=+loop ctx->me_cmp|= 1;  // cmp=+chroma, where CHROMA = 1 ctx->partitions|=X264_PART_I8X8+X264_PART_I4X4+X264_PART_P8X8+X264_PART_B8X8; // partitions=+parti8x8+parti4x4+partp8x8+partb8x8 ctx->me_method=ME_HEX;    // me_method=hex ctx->me_subpel_quality = 7;   // subq=7 ctx->me_range = 16;   // me_range=16 ctx->gop_size = 250;  // g=250 ctx->keyint_min = 25; // keyint_min=25 ctx->scenechange_threshold = 40;  // sc_threshold=40 ctx->i_quant_factor = 0.71; // i_qfactor=0.71 ctx->b_frame_strategy = 1;  // b_strategy=1 ctx->qcompress = 0.6; // qcomp=0.6 ctx->qmin = 10;   // qmin=10 ctx->qmax = 51;   // qmax=51 ctx->max_qdiff = 4;   // qdiff=4 ctx->max_b_frames = 3;    // bf=3 ctx->refs = 3;    // refs=3 ctx->directpred = 1;  // directpred=1 ctx->trellis = 1; // trellis=1 ctx->flags2|=CODEC_FLAG2_BPYRAMID+CODEC_FLAG2_MIXED_REFS+CODEC_FLAG2_WPRED+CODEC_FLAG2_8X8DCT+CODEC_FLAG2_FASTPSKIP;  // flags2=+bpyramid+mixed_refs+wpred+dct8x8+fastpskip ctx->weighted_p_pred = 2; // wpredp=2  // libx264-main.ffpreset preset ctx->flags2|=CODEC_FLAG2_8X8DCT;c->flags2^=CODEC_FLAG2_8X8DCT;    // flags2=-dct8x8 

You'll have to look at the ffmpeg source code if you want to parse those presets automatically.

I hope that the information I just gave would help you out a bit more :)