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FFmpeg源代码简单分析：avcodec_open2()_avcodec_open2() error -1: could not open video cod
作者：2023面试高手 | 2024-04-25 10:15:00
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avcodec_open2() error -1: could not open video codec.
本文简单分析FFmpeg的avcodec_open2()函数。该函数用于初始化一个视音频编解码器的AVCodecContext。
avcodec_open2()的声明位于libavcodec\avcodec.h，如下所示。
/** * Initialize the AVCodecContext to use the given AVCodec. Prior to using this * function the context has to be allocated with avcodec_alloc_context3(). * * The functions avcodec_find_decoder_by_name(), avcodec_find_encoder_by_name(), * avcodec_find_decoder() and avcodec_find_encoder() provide an easy way for * retrieving a codec. * * @warning This function is not thread safe! * * @note Always call this function before using decoding routines (such as * @ref avcodec_receive_frame()). * * @code * av_dict_set(&opts, "b", "2.5M", 0); * codec = avcodec_find_decoder(AV_CODEC_ID_H264); * if (!codec) * exit(1); * * context = avcodec_alloc_context3(codec); * * if (avcodec_open2(context, codec, opts) < 0) * exit(1); * @endcode * * @param avctx The context to initialize. * @param codec The codec to open this context for. If a non-NULL codec has been * previously passed to avcodec_alloc_context3() or * for this context, then this parameter MUST be either NULL or * equal to the previously passed codec. * @param options A dictionary filled with AVCodecContext and codec-private options. * On return this object will be filled with options that were not found. * * @return zero on success, a negative value on error * @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(), * av_dict_set(), av_opt_find(). */ int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);
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用中文简单转述一下avcodec_open2()各个参数的含义：
avctx：需要初始化的AVCodecContext。
codec：输入的AVCodec
options：一些选项。例如使用libx264编码的时候，“preset”，“tune”等都可以通过该参数设置。
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函数调用关系图
avcodec_open2()函数调用关系非常简单，如下图所示。
avcodec_open2()
avcodec_open2()的定义位于libavcodec\avcodec.c，如下所示。
int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options) { int ret = 0; int codec_init_ok = 0; AVDictionary *tmp = NULL; AVCodecInternal *avci; if (avcodec_is_open(avctx)) return 0; if (!codec && !avctx->codec) { av_log(avctx, AV_LOG_ERROR, "No codec provided to avcodec_open2()\n"); return AVERROR(EINVAL); } if (codec && avctx->codec && codec != avctx->codec) { av_log(avctx, AV_LOG_ERROR, "This AVCodecContext was allocated for %s, " "but %s passed to avcodec_open2()\n", avctx->codec->name, codec->name); return AVERROR(EINVAL); } if (!codec) codec = avctx->codec; if ((avctx->codec_type == AVMEDIA_TYPE_UNKNOWN || avctx->codec_type == codec->type) && avctx->codec_id == AV_CODEC_ID_NONE) { avctx->codec_type = codec->type; avctx->codec_id = codec->id; } if (avctx->codec_id != codec->id || (avctx->codec_type != codec->type && avctx->codec_type != AVMEDIA_TYPE_ATTACHMENT)) { av_log(avctx, AV_LOG_ERROR, "Codec type or id mismatches\n"); return AVERROR(EINVAL); } avctx->codec = codec; if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE) return AVERROR(EINVAL); if (options) av_dict_copy(&tmp, *options, 0); lock_avcodec(codec); avci = av_mallocz(sizeof(*avci)); if (!avci) { ret = AVERROR(ENOMEM); goto end; } avctx->internal = avci; #if FF_API_OLD_ENCDEC avci->to_free = av_frame_alloc(); avci->compat_decode_frame = av_frame_alloc(); avci->compat_encode_packet = av_packet_alloc(); if (!avci->to_free || !avci->compat_decode_frame || !avci->compat_encode_packet) { ret = AVERROR(ENOMEM); goto free_and_end; } #endif avci->buffer_frame = av_frame_alloc(); avci->buffer_pkt = av_packet_alloc(); avci->es.in_frame = av_frame_alloc(); avci->ds.in_pkt = av_packet_alloc(); avci->last_pkt_props = av_packet_alloc(); avci->pkt_props = av_fifo_alloc(sizeof(*avci->last_pkt_props)); if (!avci->buffer_frame || !avci->buffer_pkt || !avci->es.in_frame || !avci->ds.in_pkt || !avci->last_pkt_props || !avci->pkt_props) { ret = AVERROR(ENOMEM); goto free_and_end; } avci->skip_samples_multiplier = 1; if (codec->priv_data_size > 0) { if (!avctx->priv_data) { avctx->priv_data = av_mallocz(codec->priv_data_size); if (!avctx->priv_data) { ret = AVERROR(ENOMEM); goto free_and_end; } if (codec->priv_class) { *(const AVClass **)avctx->priv_data = codec->priv_class; av_opt_set_defaults(avctx->priv_data); } } if (codec->priv_class && (ret = av_opt_set_dict(avctx->priv_data, &tmp)) < 0) goto free_and_end; } else { avctx->priv_data = NULL; } if ((ret = av_opt_set_dict(avctx, &tmp)) < 0) goto free_and_end; if (avctx->codec_whitelist && av_match_list(codec->name, avctx->codec_whitelist, ',') <= 0) { av_log(avctx, AV_LOG_ERROR, "Codec (%s) not on whitelist \'%s\'\n", codec->name, avctx->codec_whitelist); ret = AVERROR(EINVAL); goto free_and_end; } // only call ff_set_dimensions() for non H.264/VP6F/DXV codecs so as not to overwrite previously setup dimensions if (!(avctx->coded_width && avctx->coded_height && avctx->width && avctx->height && (avctx->codec_id == AV_CODEC_ID_H264 || avctx->codec_id == AV_CODEC_ID_VP6F || avctx->codec_id == AV_CODEC_ID_DXV))) { if (avctx->coded_width && avctx->coded_height) ret = ff_set_dimensions(avctx, avctx->coded_width, avctx->coded_height); else if (avctx->width && avctx->height) ret = ff_set_dimensions(avctx, avctx->width, avctx->height); if (ret < 0) goto free_and_end; } if ((avctx->coded_width || avctx->coded_height || avctx->width || avctx->height) && ( av_image_check_size2(avctx->coded_width, avctx->coded_height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx) < 0 || av_image_check_size2(avctx->width, avctx->height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx) < 0)) { av_log(avctx, AV_LOG_WARNING, "Ignoring invalid width/height values\n"); ff_set_dimensions(avctx, 0, 0); } if (avctx->width > 0 && avctx->height > 0) { if (av_image_check_sar(avctx->width, avctx->height, avctx->sample_aspect_ratio) < 0) { av_log(avctx, AV_LOG_WARNING, "ignoring invalid SAR: %u/%u\n", avctx->sample_aspect_ratio.num, avctx->sample_aspect_ratio.den); avctx->sample_aspect_ratio = (AVRational){ 0, 1 }; } } if (avctx->channels > FF_SANE_NB_CHANNELS || avctx->channels < 0) { av_log(avctx, AV_LOG_ERROR, "Too many or invalid channels: %d\n", avctx->channels); ret = AVERROR(EINVAL); goto free_and_end; } if (avctx->sample_rate < 0) { av_log(avctx, AV_LOG_ERROR, "Invalid sample rate: %d\n", avctx->sample_rate); ret = AVERROR(EINVAL); goto free_and_end; } if (avctx->block_align < 0) { av_log(avctx, AV_LOG_ERROR, "Invalid block align: %d\n", avctx->block_align); ret = AVERROR(EINVAL); goto free_and_end; } avctx->frame_number = 0; avctx->codec_descriptor = avcodec_descriptor_get(avctx->codec_id); if ((avctx->codec->capabilities & AV_CODEC_CAP_EXPERIMENTAL) && avctx->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) { const char *codec_string = av_codec_is_encoder(codec) ? "encoder" : "decoder"; const AVCodec *codec2; av_log(avctx, AV_LOG_ERROR, "The %s '%s' is experimental but experimental codecs are not enabled, " "add '-strict %d' if you want to use it.\n", codec_string, codec->name, FF_COMPLIANCE_EXPERIMENTAL); codec2 = av_codec_is_encoder(codec) ? avcodec_find_encoder(codec->id) : avcodec_find_decoder(codec->id); if (!(codec2->capabilities & AV_CODEC_CAP_EXPERIMENTAL)) av_log(avctx, AV_LOG_ERROR, "Alternatively use the non experimental %s '%s'.\n", codec_string, codec2->name); ret = AVERROR_EXPERIMENTAL; goto free_and_end; } if (avctx->codec_type == AVMEDIA_TYPE_AUDIO && (!avctx->time_base.num || !avctx->time_base.den)) { avctx->time_base.num = 1; avctx->time_base.den = avctx->sample_rate; } if (av_codec_is_encoder(avctx->codec)) ret = ff_encode_preinit(avctx); else ret = ff_decode_preinit(avctx); if (ret < 0) goto free_and_end; if (!HAVE_THREADS) av_log(avctx, AV_LOG_WARNING, "Warning: not compiled with thread support, using thread emulation\n"); if (CONFIG_FRAME_THREAD_ENCODER && av_codec_is_encoder(avctx->codec)) { unlock_avcodec(codec); //we will instantiate a few encoders thus kick the counter to prevent false detection of a problem ret = ff_frame_thread_encoder_init(avctx, options ? *options : NULL); lock_avcodec(codec); if (ret < 0) goto free_and_end; } if (HAVE_THREADS && !(avci->frame_thread_encoder && (avctx->active_thread_type&FF_THREAD_FRAME))) { ret = ff_thread_init(avctx); if (ret < 0) { goto free_and_end; } } if (!HAVE_THREADS && !(codec->caps_internal & FF_CODEC_CAP_AUTO_THREADS)) avctx->thread_count = 1; if ( avctx->codec->init && (!(avctx->active_thread_type&FF_THREAD_FRAME) || avci->frame_thread_encoder)) { ret = avctx->codec->init(avctx); if (ret < 0) { codec_init_ok = -1; goto free_and_end; } codec_init_ok = 1; } ret=0; if (av_codec_is_decoder(avctx->codec)) { if (!avctx->bit_rate) avctx->bit_rate = get_bit_rate(avctx); /* validate channel layout from the decoder */ if (avctx->channel_layout) { int channels = av_get_channel_layout_nb_channels(avctx->channel_layout); if (!avctx->channels) avctx->channels = channels; else if (channels != avctx->channels) { char buf[512]; av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout); av_log(avctx, AV_LOG_WARNING, "Channel layout '%s' with %d channels does not match specified number of channels %d: " "ignoring specified channel layout\n", buf, channels, avctx->channels); avctx->channel_layout = 0; } } if (avctx->channels && avctx->channels < 0 || avctx->channels > FF_SANE_NB_CHANNELS) { ret = AVERROR(EINVAL); goto free_and_end; } if (avctx->bits_per_coded_sample < 0) { ret = AVERROR(EINVAL); goto free_and_end; } #if FF_API_AVCTX_TIMEBASE if (avctx->framerate.num > 0 && avctx->framerate.den > 0) avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1})); #endif } if (codec->priv_data_size > 0 && avctx->priv_data && codec->priv_class) { av_assert0(*(const AVClass **)avctx->priv_data == codec->priv_class); } end: unlock_avcodec(codec); if (options) { av_dict_free(options); *options = tmp; } return ret; free_and_end: if (avctx->codec && avctx->codec->close && (codec_init_ok > 0 || (codec_init_ok < 0 && avctx->codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP))) avctx->codec->close(avctx); if (HAVE_THREADS && avci->thread_ctx) ff_thread_free(avctx); if (codec->priv_class && avctx->priv_data) av_opt_free(avctx->priv_data); av_opt_free(avctx); if (av_codec_is_encoder(avctx->codec)) { #if FF_API_CODED_FRAME FF_DISABLE_DEPRECATION_WARNINGS av_frame_free(&avctx->coded_frame); FF_ENABLE_DEPRECATION_WARNINGS #endif av_freep(&avctx->extradata); avctx->extradata_size = 0; } av_dict_free(&tmp); av_freep(&avctx->priv_data); av_freep(&avctx->subtitle_header); #if FF_API_OLD_ENCDEC av_frame_free(&avci->to_free); av_frame_free(&avci->compat_decode_frame); av_packet_free(&avci->compat_encode_packet); #endif av_frame_free(&avci->buffer_frame); av_packet_free(&avci->buffer_pkt); av_packet_free(&avci->last_pkt_props); av_fifo_freep(&avci->pkt_props); av_packet_free(&avci->ds.in_pkt); av_frame_free(&avci->es.in_frame); av_bsf_free(&avci->bsf); av_buffer_unref(&avci->pool); av_freep(&avci); avctx->internal = NULL; avctx->codec = NULL; goto end; }
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AVCodec->init()
avcodec_open2()中最关键的一步就是调用AVCodec的init()方法初始化具体的编码器。AVCodec的init()是一个函数指针，指向具体编解码器中的初始化函数。这里我们以libx264为例，看一下它对应的AVCodec的定义。libx264对应的AVCodec的定义位于libavcodec\libx264.c，如下所示。
AVCodec ff_libx264_encoder = { .name = "libx264", .long_name = NULL_IF_CONFIG_SMALL("libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"), .type = AVMEDIA_TYPE_VIDEO, .id = AV_CODEC_ID_H264, .priv_data_size = sizeof(X264Context), .init = X264_init, .encode2 = X264_frame, .close = X264_close, .capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_OTHER_THREADS | AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE, .caps_internal = FF_CODEC_CAP_AUTO_THREADS, .priv_class = &x264_class, .defaults = x264_defaults, #if X264_BUILD < 153 .init_static_data = X264_init_static, #else .pix_fmts = pix_fmts_all, #endif .caps_internal = FF_CODEC_CAP_INIT_CLEANUP | FF_CODEC_CAP_AUTO_THREADS #if X264_BUILD >= 158 | FF_CODEC_CAP_INIT_THREADSAFE #endif , .wrapper_name = "libx264", };
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可以看出在ff_libx264_encoder中init()指向X264_init()。X264_init()的定义同样位于libavcodec\libx264.c，如下所示。
static av_cold int X264_init(AVCodecContext *avctx) { X264Context *x4 = avctx->priv_data; AVCPBProperties *cpb_props; int sw,sh; int ret; if (avctx->global_quality > 0) av_log(avctx, AV_LOG_WARNING, "-qscale is ignored, -crf is recommended.\n"); x264_param_default(&x4->params); x4->params.b_deblocking_filter = avctx->flags & AV_CODEC_FLAG_LOOP_FILTER; if (x4->preset || x4->tune) if (x264_param_default_preset(&x4->params, x4->preset, x4->tune) < 0) { int i; av_log(avctx, AV_LOG_ERROR, "Error setting preset/tune %s/%s.\n", x4->preset, x4->tune); av_log(avctx, AV_LOG_INFO, "Possible presets:"); for (i = 0; x264_preset_names[i]; i++) av_log(avctx, AV_LOG_INFO, " %s", x264_preset_names[i]); av_log(avctx, AV_LOG_INFO, "\n"); av_log(avctx, AV_LOG_INFO, "Possible tunes:"); for (i = 0; x264_tune_names[i]; i++) av_log(avctx, AV_LOG_INFO, " %s", x264_tune_names[i]); av_log(avctx, AV_LOG_INFO, "\n"); return AVERROR(EINVAL); } if (avctx->level > 0) x4->params.i_level_idc = avctx->level; x4->params.pf_log = X264_log; x4->params.p_log_private = avctx; x4->params.i_log_level = X264_LOG_DEBUG; x4->params.i_csp = convert_pix_fmt(avctx->pix_fmt); PARSE_X264_OPT("weightp", wpredp); if (avctx->bit_rate) { if (avctx->bit_rate / 1000 > INT_MAX || avctx->rc_max_rate / 1000 > INT_MAX) { av_log(avctx, AV_LOG_ERROR, "bit_rate and rc_max_rate > %d000 not supported by libx264\n", INT_MAX); return AVERROR(EINVAL); } x4->params.rc.i_bitrate = avctx->bit_rate / 1000; x4->params.rc.i_rc_method = X264_RC_ABR; } x4->params.rc.i_vbv_buffer_size = avctx->rc_buffer_size / 1000; x4->params.rc.i_vbv_max_bitrate = avctx->rc_max_rate / 1000; x4->params.rc.b_stat_write = avctx->flags & AV_CODEC_FLAG_PASS1; if (avctx->flags & AV_CODEC_FLAG_PASS2) { x4->params.rc.b_stat_read = 1; } else { if (x4->crf >= 0) { x4->params.rc.i_rc_method = X264_RC_CRF; x4->params.rc.f_rf_constant = x4->crf; } else if (x4->cqp >= 0) { x4->params.rc.i_rc_method = X264_RC_CQP; x4->params.rc.i_qp_constant = x4->cqp; } if (x4->crf_max >= 0) x4->params.rc.f_rf_constant_max = x4->crf_max; } if (avctx->rc_buffer_size && avctx->rc_initial_buffer_occupancy > 0 && (avctx->rc_initial_buffer_occupancy <= avctx->rc_buffer_size)) { x4->params.rc.f_vbv_buffer_init = (float)avctx->rc_initial_buffer_occupancy / avctx->rc_buffer_size; } PARSE_X264_OPT("level", level); if (avctx->i_quant_factor > 0) x4->params.rc.f_ip_factor = 1 / fabs(avctx->i_quant_factor); if (avctx->b_quant_factor > 0) x4->params.rc.f_pb_factor = avctx->b_quant_factor; if (x4->chroma_offset) x4->params.analyse.i_chroma_qp_offset = x4->chroma_offset; if (avctx->gop_size >= 0) x4->params.i_keyint_max = avctx->gop_size; if (avctx->max_b_frames >= 0) x4->params.i_bframe = avctx->max_b_frames; #if FF_API_PRIVATE_OPT FF_DISABLE_DEPRECATION_WARNINGS if (avctx->scenechange_threshold >= 0) x4->scenechange_threshold = avctx->scenechange_threshold; FF_ENABLE_DEPRECATION_WARNINGS #endif if (x4->scenechange_threshold >= 0) x4->params.i_scenecut_threshold = x4->scenechange_threshold; if (avctx->qmin >= 0) x4->params.rc.i_qp_min = avctx->qmin; if (avctx->qmax >= 0) x4->params.rc.i_qp_max = avctx->qmax; if (avctx->max_qdiff >= 0) x4->params.rc.i_qp_step = avctx->max_qdiff; if (avctx->qblur >= 0) x4->params.rc.f_qblur = avctx->qblur; /* temporally blur quants */ if (avctx->qcompress >= 0) x4->params.rc.f_qcompress = avctx->qcompress; /* 0.0 => cbr, 1.0 => constant qp */ if (avctx->refs >= 0) x4->params.i_frame_reference = avctx->refs; else if (x4->params.i_level_idc > 0) { int i; int mbn = AV_CEIL_RSHIFT(avctx->width, 4) * AV_CEIL_RSHIFT(avctx->height, 4); int scale = X264_BUILD < 129 ? 384 : 1; for (i = 0; i<x264_levels[i].level_idc; i++) if (x264_levels[i].level_idc == x4->params.i_level_idc) x4->params.i_frame_reference = av_clip(x264_levels[i].dpb / mbn / scale, 1, x4->params.i_frame_reference); } if (avctx->trellis >= 0) x4->params.analyse.i_trellis = avctx->trellis; if (avctx->me_range >= 0) x4->params.analyse.i_me_range = avctx->me_range; if (x4->noise_reduction >= 0) x4->params.analyse.i_noise_reduction = x4->noise_reduction; if (avctx->me_subpel_quality >= 0) x4->params.analyse.i_subpel_refine = avctx->me_subpel_quality; if (avctx->keyint_min >= 0) x4->params.i_keyint_min = avctx->keyint_min; if (avctx->me_cmp >= 0) x4->params.analyse.b_chroma_me = avctx->me_cmp & FF_CMP_CHROMA; if (x4->aq_mode >= 0) x4->params.rc.i_aq_mode = x4->aq_mode; if (x4->aq_strength >= 0) x4->params.rc.f_aq_strength = x4->aq_strength; PARSE_X264_OPT("psy-rd", psy_rd); PARSE_X264_OPT("deblock", deblock); PARSE_X264_OPT("partitions", partitions); PARSE_X264_OPT("stats", stats); if (x4->psy >= 0) x4->params.analyse.b_psy = x4->psy; if (x4->rc_lookahead >= 0) x4->params.rc.i_lookahead = x4->rc_lookahead; if (x4->weightp >= 0) x4->params.analyse.i_weighted_pred = x4->weightp; if (x4->weightb >= 0) x4->params.analyse.b_weighted_bipred = x4->weightb; if (x4->cplxblur >= 0) x4->params.rc.f_complexity_blur = x4->cplxblur; if (x4->ssim >= 0) x4->params.analyse.b_ssim = x4->ssim; if (x4->intra_refresh >= 0) x4->params.b_intra_refresh = x4->intra_refresh; if (x4->bluray_compat >= 0) { x4->params.b_bluray_compat = x4->bluray_compat; x4->params.b_vfr_input = 0; } if (x4->avcintra_class >= 0) av_log(avctx, AV_LOG_ERROR, "x264 too old for AVC Intra, at least version 142 needed\n"); if (x4->b_bias != INT_MIN) x4->params.i_bframe_bias = x4->b_bias; if (x4->b_pyramid >= 0) x4->params.i_bframe_pyramid = x4->b_pyramid; if (x4->mixed_refs >= 0) x4->params.analyse.b_mixed_references = x4->mixed_refs; if (x4->dct8x8 >= 0) x4->params.analyse.b_transform_8x8 = x4->dct8x8; if (x4->fast_pskip >= 0) x4->params.analyse.b_fast_pskip = x4->fast_pskip; if (x4->aud >= 0) x4->params.b_aud = x4->aud; if (x4->mbtree >= 0) x4->params.rc.b_mb_tree = x4->mbtree; if (x4->direct_pred >= 0) x4->params.analyse.i_direct_mv_pred = x4->direct_pred; if (x4->slice_max_size >= 0) x4->params.i_slice_max_size = x4->slice_max_size; if (x4->fastfirstpass) x264_param_apply_fastfirstpass(&x4->params); /* Allow specifying the x264 profile through AVCodecContext. */ if (!x4->profile) switch (avctx->profile) { case FF_PROFILE_H264_BASELINE: x4->profile = av_strdup("baseline"); break; case FF_PROFILE_H264_HIGH: x4->profile = av_strdup("high"); break; case FF_PROFILE_H264_HIGH_10: x4->profile = av_strdup("high10"); break; case FF_PROFILE_H264_HIGH_422: x4->profile = av_strdup("high422"); break; case FF_PROFILE_H264_HIGH_444: x4->profile = av_strdup("high444"); break; case FF_PROFILE_H264_MAIN: x4->profile = av_strdup("main"); break; default: break; } if (x4->nal_hrd >= 0) x4->params.i_nal_hrd = x4->nal_hrd; if (x4->motion_est >= 0) x4->params.analyse.i_me_method = x4->motion_est; if (x4->coder >= 0) x4->params.b_cabac = x4->coder; if (x4->b_frame_strategy >= 0) x4->params.i_bframe_adaptive = x4->b_frame_strategy; if (x4->profile) if (x264_param_apply_profile(&x4->params, x4->profile) < 0) { int i; av_log(avctx, AV_LOG_ERROR, "Error setting profile %s.\n", x4->profile); av_log(avctx, AV_LOG_INFO, "Possible profiles:"); for (i = 0; x264_profile_names[i]; i++) av_log(avctx, AV_LOG_INFO, " %s", x264_profile_names[i]); av_log(avctx, AV_LOG_INFO, "\n"); return AVERROR(EINVAL); } x4->params.i_width = avctx->width; x4->params.i_height = avctx->height; av_reduce(&sw, &sh, avctx->sample_aspect_ratio.num, avctx->sample_aspect_ratio.den, 4096); x4->params.vui.i_sar_width = sw; x4->params.vui.i_sar_height = sh; x4->params.i_timebase_den = avctx->time_base.den; x4->params.i_timebase_num = avctx->time_base.num; if (avctx->framerate.num > 0 && avctx->framerate.den > 0) { x4->params.i_fps_num = avctx->framerate.num; x4->params.i_fps_den = avctx->framerate.den; } else { x4->params.i_fps_num = avctx->time_base.den; x4->params.i_fps_den = avctx->time_base.num * avctx->ticks_per_frame; } x4->params.analyse.b_psnr = avctx->flags & AV_CODEC_FLAG_PSNR; x4->params.i_threads = avctx->thread_count; if (avctx->thread_type) x4->params.b_sliced_threads = avctx->thread_type == FF_THREAD_SLICE; x4->params.b_interlaced = avctx->flags & AV_CODEC_FLAG_INTERLACED_DCT; x4->params.b_open_gop = !(avctx->flags & AV_CODEC_FLAG_CLOSED_GOP); x4->params.i_slice_count = avctx->slices; x4->params.vui.b_fullrange = avctx->pix_fmt == AV_PIX_FMT_YUVJ420P || avctx->pix_fmt == AV_PIX_FMT_YUVJ422P || avctx->pix_fmt == AV_PIX_FMT_YUVJ444P || avctx->color_range == AVCOL_RANGE_JPEG; if (avctx->colorspace != AVCOL_SPC_UNSPECIFIED) x4->params.vui.i_colmatrix = avctx->colorspace; if (avctx->color_primaries != AVCOL_PRI_UNSPECIFIED) x4->params.vui.i_colorprim = avctx->color_primaries; if (avctx->color_trc != AVCOL_TRC_UNSPECIFIED) x4->params.vui.i_transfer = avctx->color_trc; if (avctx->flags & AV_CODEC_FLAG_GLOBAL_HEADER) x4->params.b_repeat_headers = 0; if(x4->x264opts){ const char *p= x4->x264opts; while(p){ char param[4096]={0}, val[4096]={0}; if(sscanf(p, "%4095[^:=]=%4095[^:]", param, val) == 1){ ret = parse_opts(avctx, param, "1"); if (ret < 0) return ret; } else { ret = parse_opts(avctx, param, val); if (ret < 0) return ret; } p= strchr(p, ':'); p+=!!p; } } { AVDictionaryEntry *en = NULL; while (en = av_dict_get(x4->x264_params, "", en, AV_DICT_IGNORE_SUFFIX)) { if ((ret = x264_param_parse(&x4->params, en->key, en->value)) < 0) { av_log(avctx, AV_LOG_WARNING, "Error parsing option '%s = %s'.\n", en->key, en->value); } } } // update AVCodecContext with x264 parameters avctx->has_b_frames = x4->params.i_bframe ? x4->params.i_bframe_pyramid ? 2 : 1 : 0; if (avctx->max_b_frames < 0) avctx->max_b_frames = 0; avctx->bit_rate = x4->params.rc.i_bitrate*1000LL; x4->enc = x264_encoder_open(&x4->params); if (!x4->enc) return AVERROR_EXTERNAL; if (avctx->flags & AV_CODEC_FLAG_GLOBAL_HEADER) { x264_nal_t *nal; uint8_t *p; int nnal, s, i; s = x264_encoder_headers(x4->enc, &nal, &nnal); avctx->extradata = p = av_mallocz(s + AV_INPUT_BUFFER_PADDING_SIZE); if (!p) return AVERROR(ENOMEM); for (i = 0; i < nnal; i++) { /* Don't put the SEI in extradata. */ if (nal[i].i_type == NAL_SEI) { av_log(avctx, AV_LOG_INFO, "%s\n", nal[i].p_payload+25); x4->sei_size = nal[i].i_payload; x4->sei = av_malloc(x4->sei_size); if (!x4->sei) return AVERROR(ENOMEM); memcpy(x4->sei, nal[i].p_payload, nal[i].i_payload); continue; } memcpy(p, nal[i].p_payload, nal[i].i_payload); p += nal[i].i_payload; } avctx->extradata_size = p - avctx->extradata; } cpb_props = ff_add_cpb_side_data(avctx); if (!cpb_props) return AVERROR(ENOMEM); cpb_props->buffer_size = x4->params.rc.i_vbv_buffer_size * 1000; cpb_props->max_bitrate = x4->params.rc.i_vbv_max_bitrate * 1000LL; cpb_props->avg_bitrate = x4->params.rc.i_bitrate * 1000LL; // Overestimate the reordered opaque buffer size, in case a runtime // reconfigure would increase the delay (which it shouldn't). x4->nb_reordered_opaque = x264_encoder_maximum_delayed_frames(x4->enc) + 17; x4->reordered_opaque = av_malloc_array(x4->nb_reordered_opaque, sizeof(*x4->reordered_opaque)); if (!x4->reordered_opaque) return AVERROR(ENOMEM); return 0; }
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X264_init()的代码以后研究X264的时候再进行细节的分析，在这里简单记录一下它做的两项工作：
（1）设置X264Context的参数。X264Context主要完成了libx264和FFmpeg对接的功能。可以看出代码主要在设置一个params结构体变量，该变量的类型即是x264中存储参数的结构体x264_param_t。
（2）调用libx264的API进行编码器的初始化工作。例如调用x264_param_default()设置默认参数，调用x264_param_apply_profile()设置profile，调用x264_encoder_open()打开编码器等等。
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最后附上X264Context的定义，位于libavcodec\libx264.c，如下所示。
typedef struct X264Context { AVClass *class; x264_param_t params; x264_t *enc; x264_picture_t pic; uint8_t *sei; int sei_size; char *preset; char *tune; char *profile; char *level; int fastfirstpass; char *wpredp; char *x264opts; float crf; float crf_max; int cqp; int aq_mode; float aq_strength; char *psy_rd; int psy; int rc_lookahead; int weightp; int weightb; int ssim; int intra_refresh; int bluray_compat; int b_bias; int b_pyramid; int mixed_refs; int dct8x8; int fast_pskip; int aud; int mbtree; char *deblock; float cplxblur; char *partitions; int direct_pred; int slice_max_size; char *stats; int nal_hrd; int avcintra_class; int motion_est; int forced_idr; int coder; int a53_cc; int b_frame_strategy; int chroma_offset; int scenechange_threshold; int noise_reduction; AVDictionary *x264_params; int nb_reordered_opaque, next_reordered_opaque; X264Opaque *reordered_opaque; /** * If the encoder does not support ROI then warn the first time we * encounter a frame with ROI side data. */ int roi_warned; } X264Context;
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参考文献
1、https://blog.csdn.net/leixiaohua1020/article/details/44117891
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