初始化AVCodecContext
/** * 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 * avcodec_register_all(); * 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);
实现
int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options) { int ret = 0; int codec_init_ok = 0; AVDictionary *tmp = NULL; const AVPixFmtDescriptor *pixdesc; 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->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE) return AVERROR(EINVAL); if (options) av_dict_copy(&tmp, *options, 0); // 添加锁codec_mutex ff_lock_avcodec(avctx, codec); // 为各个成员分配内存 avctx->internal = av_mallocz(sizeof(*avctx->internal)); if (!avctx->internal) { ret = AVERROR(ENOMEM); goto end; } avctx->internal->pool = av_mallocz(sizeof(*avctx->internal->pool)); if (!avctx->internal->pool) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->to_free = av_frame_alloc(); if (!avctx->internal->to_free) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->compat_decode_frame = av_frame_alloc(); if (!avctx->internal->compat_decode_frame) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->buffer_frame = av_frame_alloc(); if (!avctx->internal->buffer_frame) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->buffer_pkt = av_packet_alloc(); if (!avctx->internal->buffer_pkt) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->ds.in_pkt = av_packet_alloc(); if (!avctx->internal->ds.in_pkt) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->last_pkt_props = av_packet_alloc(); if (!avctx->internal->last_pkt_props) { ret = AVERROR(ENOMEM); goto free_and_end; } avctx->internal->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 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; } // 将用户的配置设置到AVCodecContext 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; } // 检查宽和高 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); } // 检查宽高比是否有效 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 the decoder init function was already called previously, * free the already allocated subtitle_header before overwriting it */ if (av_codec_is_decoder(codec)) av_freep(&avctx->subtitle_header); if (avctx->channels > FF_SANE_NB_CHANNELS) { av_log(avctx, AV_LOG_ERROR, "Too many channels: %d\n", avctx->channels); ret = AVERROR(EINVAL); goto free_and_end; } avctx->codec = 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"); ret = AVERROR(EINVAL); goto free_and_end; } avctx->frame_number = 0; avctx->codec_descriptor = avcodec_descriptor_get(avctx->codec_id); // 检查编码器是否是实验性编码器 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"; 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 (!HAVE_THREADS) av_log(avctx, AV_LOG_WARNING, "Warning: not compiled with thread support, using thread emulation\n"); // 如果是编码器，就初始化编码器线程 if (CONFIG_FRAME_THREAD_ENCODER && av_codec_is_encoder(avctx->codec)) { ff_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); ff_lock_avcodec(avctx, codec); if (ret < 0) goto free_and_end; } // 如果是解码器，过滤器列表初始化 if (av_codec_is_decoder(avctx->codec)) { ret = ff_decode_bsfs_init(avctx); if (ret < 0) goto free_and_end; } if (HAVE_THREADS && !(avctx->internal->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->capabilities & AV_CODEC_CAP_AUTO_THREADS)) avctx->thread_count = 1; if (avctx->codec->max_lowres < avctx->lowres || avctx->lowres < 0) { av_log(avctx, AV_LOG_WARNING, "The maximum value for lowres supported by the decoder is %d\n", avctx->codec->max_lowres); avctx->lowres = avctx->codec->max_lowres; } // 编码器入参检查 if (av_codec_is_encoder(avctx->codec)) { int i; #if FF_API_CODED_FRAME FF_DISABLE_DEPRECATION_WARNINGS avctx->coded_frame = av_frame_alloc(); if (!avctx->coded_frame) { ret = AVERROR(ENOMEM); goto free_and_end; } FF_ENABLE_DEPRECATION_WARNINGS #endif if (avctx->time_base.num <= 0 || avctx->time_base.den <= 0) { av_log(avctx, AV_LOG_ERROR, "The encoder timebase is not set.\n"); ret = AVERROR(EINVAL); goto free_and_end; } // 检查采样率 if (avctx->codec->sample_fmts) { for (i = 0; avctx->codec->sample_fmts[i] != AV_SAMPLE_FMT_NONE; i++) { if (avctx->sample_fmt == avctx->codec->sample_fmts[i]) break; if (avctx->channels == 1 && av_get_planar_sample_fmt(avctx->sample_fmt) == av_get_planar_sample_fmt(avctx->codec->sample_fmts[i])) { avctx->sample_fmt = avctx->codec->sample_fmts[i]; break; } } if (avctx->codec->sample_fmts[i] == AV_SAMPLE_FMT_NONE) { char buf[128]; snprintf(buf, sizeof(buf), "%d", avctx->sample_fmt); av_log(avctx, AV_LOG_ERROR, "Specified sample format %s is invalid or not supported\n", (char *)av_x_if_null(av_get_sample_fmt_name(avctx->sample_fmt), buf)); ret = AVERROR(EINVAL); goto free_and_end; } } // 检查分辨率 if (avctx->codec->pix_fmts) { for (i = 0; avctx->codec->pix_fmts[i] != AV_PIX_FMT_NONE; i++) if (avctx->pix_fmt == avctx->codec->pix_fmts[i]) break; if (avctx->codec->pix_fmts[i] == AV_PIX_FMT_NONE && !((avctx->codec_id == AV_CODEC_ID_MJPEG || avctx->codec_id == AV_CODEC_ID_LJPEG) && avctx->strict_std_compliance <= FF_COMPLIANCE_UNOFFICIAL)) { char buf[128]; snprintf(buf, sizeof(buf), "%d", avctx->pix_fmt); av_log(avctx, AV_LOG_ERROR, "Specified pixel format %s is invalid or not supported\n", (char *)av_x_if_null(av_get_pix_fmt_name(avctx->pix_fmt), buf)); ret = AVERROR(EINVAL); goto free_and_end; } if (avctx->codec->pix_fmts[i] == AV_PIX_FMT_YUVJ420P || avctx->codec->pix_fmts[i] == AV_PIX_FMT_YUVJ411P || avctx->codec->pix_fmts[i] == AV_PIX_FMT_YUVJ422P || avctx->codec->pix_fmts[i] == AV_PIX_FMT_YUVJ440P || avctx->codec->pix_fmts[i] == AV_PIX_FMT_YUVJ444P) avctx->color_range = AVCOL_RANGE_JPEG; } // 检查支持的采样率 if (avctx->codec->supported_samplerates) { for (i = 0; avctx->codec->supported_samplerates[i] != 0; i++) if (avctx->sample_rate == avctx->codec->supported_samplerates[i]) break; if (avctx->codec->supported_samplerates[i] == 0) { av_log(avctx, AV_LOG_ERROR, "Specified sample rate %d is not supported\n", avctx->sample_rate); ret = AVERROR(EINVAL); goto free_and_end; } } if (avctx->sample_rate < 0) { av_log(avctx, AV_LOG_ERROR, "Specified sample rate %d is not supported\n", avctx->sample_rate); ret = AVERROR(EINVAL); goto free_and_end; } // 检查通道数 if (avctx->codec->channel_layouts) { if (!avctx->channel_layout) { av_log(avctx, AV_LOG_WARNING, "Channel layout not specified\n"); } else { for (i = 0; avctx->codec->channel_layouts[i] != 0; i++) if (avctx->channel_layout == avctx->codec->channel_layouts[i]) break; if (avctx->codec->channel_layouts[i] == 0) { char buf[512]; av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout); av_log(avctx, AV_LOG_ERROR, "Specified channel layout '%s' is not supported\n", buf); ret = AVERROR(EINVAL); goto free_and_end; } } } if (avctx->channel_layout && avctx->channels) { int channels = av_get_channel_layout_nb_channels(avctx->channel_layout); if (channels != avctx->channels) { char buf[512]; av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout); av_log(avctx, AV_LOG_ERROR, "Channel layout '%s' with %d channels does not match number of specified channels %d\n", buf, channels, avctx->channels); ret = AVERROR(EINVAL); goto free_and_end; } } else if (avctx->channel_layout) { avctx->channels = av_get_channel_layout_nb_channels(avctx->channel_layout); } if (avctx->channels < 0) { av_log(avctx, AV_LOG_ERROR, "Specified number of channels %d is not supported\n", avctx->channels); ret = AVERROR(EINVAL); goto free_and_end; } // 视频：设置采样位数 if(avctx->codec_type == AVMEDIA_TYPE_VIDEO) { pixdesc = av_pix_fmt_desc_get(avctx->pix_fmt); if ( avctx->bits_per_raw_sample < 0 || (avctx->bits_per_raw_sample > 8 && pixdesc->comp[0].depth <= 8)) { av_log(avctx, AV_LOG_WARNING, "Specified bit depth %d not possible with the specified pixel formats depth %d\n", avctx->bits_per_raw_sample, pixdesc->comp[0].depth); avctx->bits_per_raw_sample = pixdesc->comp[0].depth; } if (avctx->width <= 0 || avctx->height <= 0) { av_log(avctx, AV_LOG_ERROR, "dimensions not set\n"); ret = AVERROR(EINVAL); goto free_and_end; } } if ( (avctx->codec_type == AVMEDIA_TYPE_VIDEO || avctx->codec_type == AVMEDIA_TYPE_AUDIO) && avctx->bit_rate>0 && avctx->bit_rate<1000) { av_log(avctx, AV_LOG_WARNING, "Bitrate %"PRId64" is extremely low, maybe you mean %"PRId64"k\n", avctx->bit_rate, avctx->bit_rate); } if (!avctx->rc_initial_buffer_occupancy) avctx->rc_initial_buffer_occupancy = avctx->rc_buffer_size * 3LL / 4; if (avctx->ticks_per_frame && avctx->time_base.num && avctx->ticks_per_frame > INT_MAX / avctx->time_base.num) { av_log(avctx, AV_LOG_ERROR, "ticks_per_frame %d too large for the timebase %d/%d.", avctx->ticks_per_frame, avctx->time_base.num, avctx->time_base.den); goto free_and_end; } // 检查硬解码 if (avctx->hw_frames_ctx) { AVHWFramesContext *frames_ctx = (AVHWFramesContext*)avctx->hw_frames_ctx->data; if (frames_ctx->format != avctx->pix_fmt) { av_log(avctx, AV_LOG_ERROR, "Mismatching AVCodecContext.pix_fmt and AVHWFramesContext.format\n"); ret = AVERROR(EINVAL); goto free_and_end; } if (avctx->sw_pix_fmt != AV_PIX_FMT_NONE && avctx->sw_pix_fmt != frames_ctx->sw_format) { av_log(avctx, AV_LOG_ERROR, "Mismatching AVCodecContext.sw_pix_fmt (%s) " "and AVHWFramesContext.sw_format (%s)\n", av_get_pix_fmt_name(avctx->sw_pix_fmt), av_get_pix_fmt_name(frames_ctx->sw_format)); ret = AVERROR(EINVAL); goto free_and_end; } avctx->sw_pix_fmt = frames_ctx->sw_format; } } avctx->pts_correction_num_faulty_pts = avctx->pts_correction_num_faulty_dts = 0; avctx->pts_correction_last_pts = avctx->pts_correction_last_dts = INT64_MIN; if ( !CONFIG_GRAY && avctx->flags & AV_CODEC_FLAG_GRAY && avctx->codec_descriptor->type == AVMEDIA_TYPE_VIDEO) av_log(avctx, AV_LOG_WARNING, "gray decoding requested but not enabled at configuration time\n"); // 编码器初始化 if ( avctx->codec->init && (!(avctx->active_thread_type&FF_THREAD_FRAME) || avctx->internal->frame_thread_encoder)) { ret = avctx->codec->init(avctx); if (ret < 0) { goto free_and_end; } codec_init_ok = 1; } ret=0; // 解码器入参检查 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 (avctx->sub_charenc) { if (avctx->codec_type != AVMEDIA_TYPE_SUBTITLE) { av_log(avctx, AV_LOG_ERROR, "Character encoding is only " "supported with subtitles codecs\n"); ret = AVERROR(EINVAL); goto free_and_end; } else if (avctx->codec_descriptor->props & AV_CODEC_PROP_BITMAP_SUB) { av_log(avctx, AV_LOG_WARNING, "Codec '%s' is bitmap-based, " "subtitles character encoding will be ignored\n", avctx->codec_descriptor->name); avctx->sub_charenc_mode = FF_SUB_CHARENC_MODE_DO_NOTHING; } else { /* input character encoding is set for a text based subtitle * codec at this point */ if (avctx->sub_charenc_mode == FF_SUB_CHARENC_MODE_AUTOMATIC) avctx->sub_charenc_mode = FF_SUB_CHARENC_MODE_PRE_DECODER; if (avctx->sub_charenc_mode == FF_SUB_CHARENC_MODE_PRE_DECODER) { #if CONFIG_ICONV iconv_t cd = iconv_open("UTF-8", avctx->sub_charenc); if (cd == (iconv_t)-1) { ret = AVERROR(errno); av_log(avctx, AV_LOG_ERROR, "Unable to open iconv context " "with input character encoding \"%s\"\n", avctx->sub_charenc); goto free_and_end; } iconv_close(cd); #else av_log(avctx, AV_LOG_ERROR, "Character encoding subtitles " "conversion needs a libavcodec built with iconv support " "for this codec\n"); ret = AVERROR(ENOSYS); goto free_and_end; #endif } } } #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: // 解锁 ff_unlock_avcodec(codec); if (options) { av_dict_free(options); *options = tmp; } return ret; free_and_end: // 失败会释放申请的相关内存 if (avctx->codec && avctx->codec->close && (codec_init_ok || (avctx->codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP))) avctx->codec->close(avctx); if (codec->priv_class && codec->priv_data_size) av_opt_free(avctx->priv_data); av_opt_free(avctx); #if FF_API_CODED_FRAME FF_DISABLE_DEPRECATION_WARNINGS av_frame_free(&avctx->coded_frame); FF_ENABLE_DEPRECATION_WARNINGS #endif av_dict_free(&tmp); av_freep(&avctx->priv_data); av_freep(&avctx->subtitle_header); if (avctx->internal) { av_frame_free(&avctx->internal->to_free); av_frame_free(&avctx->internal->compat_decode_frame); av_frame_free(&avctx->internal->buffer_frame); av_packet_free(&avctx->internal->buffer_pkt); av_packet_free(&avctx->internal->last_pkt_props); av_packet_free(&avctx->internal->ds.in_pkt); ff_decode_bsfs_uninit(avctx); av_freep(&avctx->internal->pool); } av_freep(&avctx->internal); avctx->codec = NULL; goto end; }
这个函数内容蛮多的，主要分为几个方面：
- 为各个成员分配内存
- 做一些参数检查
- 如果是编码器：线程初始化
- 如果是解码器：bsfs初始化
- 编码器初始化:avctx->codec->init(avctx);
- 函数会加锁保护，非线程安全
- 失败会释放申请的内存