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* This file is part of Libav.
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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* Join multiple audio inputs as different channels in
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#include "libavutil/avassert.h"
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#include "libavutil/channel_layout.h"
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#include "libavutil/common.h"
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#include "libavutil/opt.h"
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typedef struct ChannelMap {
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int input; ///< input stream index
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int in_channel_idx; ///< index of in_channel in the input stream data
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uint64_t in_channel; ///< layout describing the input channel
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uint64_t out_channel; ///< layout describing the output channel
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typedef struct JoinContext {
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char *channel_layout_str;
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uint64_t channel_layout;
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* Temporary storage for input frames, until we get one on each input.
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AVFilterBufferRef **input_frames;
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* Temporary storage for data pointers, for assembling the output buffer.
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* To avoid copying the data from input buffers, this filter creates
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* a custom output buffer that stores references to all inputs and
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* unrefs them on free.
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typedef struct JoinBufferPriv {
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AVFilterBufferRef **in_buffers;
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#define OFFSET(x) offsetof(JoinContext, x)
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#define A AV_OPT_FLAG_AUDIO_PARAM
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static const AVOption join_options[] = {
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{ "inputs", "Number of input streams.", OFFSET(inputs), AV_OPT_TYPE_INT, { .i64 = 2 }, 1, INT_MAX, A },
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{ "channel_layout", "Channel layout of the "
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"output stream.", OFFSET(channel_layout_str), AV_OPT_TYPE_STRING, {.str = "stereo"}, 0, 0, A },
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{ "map", "A comma-separated list of channels maps in the format "
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"'input_stream.input_channel-output_channel.",
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OFFSET(map), AV_OPT_TYPE_STRING, .flags = A },
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static const AVClass join_class = {
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.class_name = "join filter",
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.item_name = av_default_item_name,
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.option = join_options,
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.version = LIBAVUTIL_VERSION_INT,
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static int filter_frame(AVFilterLink *link, AVFilterBufferRef *buf)
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AVFilterContext *ctx = link->dst;
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JoinContext *s = ctx->priv;
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for (i = 0; i < ctx->nb_inputs; i++)
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if (link == ctx->inputs[i])
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av_assert0(i < ctx->nb_inputs);
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av_assert0(!s->input_frames[i]);
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s->input_frames[i] = buf;
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static int parse_maps(AVFilterContext *ctx)
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JoinContext *s = ctx->priv;
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while (cur && *cur) {
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char *sep, *next, *p;
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uint64_t in_channel = 0, out_channel = 0;
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int input_idx, out_ch_idx, in_ch_idx;
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next = strchr(cur, ',');
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/* split the map into input and output parts */
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if (!(sep = strchr(cur, '-'))) {
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av_log(ctx, AV_LOG_ERROR, "Missing separator '-' in channel "
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return AVERROR(EINVAL);
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#define PARSE_CHANNEL(str, var, inout) \
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if (!(var = av_get_channel_layout(str))) { \
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av_log(ctx, AV_LOG_ERROR, "Invalid " inout " channel: %s.\n", str);\
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return AVERROR(EINVAL); \
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if (av_get_channel_layout_nb_channels(var) != 1) { \
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av_log(ctx, AV_LOG_ERROR, "Channel map describes more than one " \
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inout " channel.\n"); \
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return AVERROR(EINVAL); \
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/* parse output channel */
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PARSE_CHANNEL(sep, out_channel, "output");
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if (!(out_channel & s->channel_layout)) {
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av_log(ctx, AV_LOG_ERROR, "Output channel '%s' is not present in "
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"requested channel layout.\n", sep);
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return AVERROR(EINVAL);
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out_ch_idx = av_get_channel_layout_channel_index(s->channel_layout,
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if (s->channels[out_ch_idx].input >= 0) {
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av_log(ctx, AV_LOG_ERROR, "Multiple maps for output channel "
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return AVERROR(EINVAL);
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/* parse input channel */
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input_idx = strtol(cur, &cur, 0);
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if (input_idx < 0 || input_idx >= s->inputs) {
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av_log(ctx, AV_LOG_ERROR, "Invalid input stream index: %d.\n",
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return AVERROR(EINVAL);
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in_ch_idx = strtol(cur, &p, 0);
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/* channel specifier is not a number,
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* try to parse as channel name */
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PARSE_CHANNEL(cur, in_channel, "input");
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s->channels[out_ch_idx].input = input_idx;
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s->channels[out_ch_idx].in_channel = in_channel;
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s->channels[out_ch_idx].in_channel_idx = in_ch_idx;
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static int join_init(AVFilterContext *ctx, const char *args)
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JoinContext *s = ctx->priv;
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s->class = &join_class;
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av_opt_set_defaults(s);
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if ((ret = av_set_options_string(s, args, "=", ":")) < 0) {
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av_log(ctx, AV_LOG_ERROR, "Error parsing options string '%s'.\n", args);
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if (!(s->channel_layout = av_get_channel_layout(s->channel_layout_str))) {
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av_log(ctx, AV_LOG_ERROR, "Error parsing channel layout '%s'.\n",
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s->channel_layout_str);
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ret = AVERROR(EINVAL);
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s->nb_channels = av_get_channel_layout_nb_channels(s->channel_layout);
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s->channels = av_mallocz(sizeof(*s->channels) * s->nb_channels);
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s->data = av_mallocz(sizeof(*s->data) * s->nb_channels);
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s->input_frames = av_mallocz(sizeof(*s->input_frames) * s->inputs);
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if (!s->channels || !s->data || !s->input_frames) {
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ret = AVERROR(ENOMEM);
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for (i = 0; i < s->nb_channels; i++) {
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s->channels[i].out_channel = av_channel_layout_extract_channel(s->channel_layout, i);
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s->channels[i].input = -1;
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if ((ret = parse_maps(ctx)) < 0)
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for (i = 0; i < s->inputs; i++) {
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AVFilterPad pad = { 0 };
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snprintf(name, sizeof(name), "input%d", i);
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pad.type = AVMEDIA_TYPE_AUDIO;
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pad.name = av_strdup(name);
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pad.filter_frame = filter_frame;
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ff_insert_inpad(ctx, i, &pad);
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static void join_uninit(AVFilterContext *ctx)
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JoinContext *s = ctx->priv;
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for (i = 0; i < ctx->nb_inputs; i++) {
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av_freep(&ctx->input_pads[i].name);
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avfilter_unref_bufferp(&s->input_frames[i]);
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av_freep(&s->channels);
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av_freep(&s->input_frames);
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static int join_query_formats(AVFilterContext *ctx)
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JoinContext *s = ctx->priv;
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AVFilterChannelLayouts *layouts = NULL;
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ff_add_channel_layout(&layouts, s->channel_layout);
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ff_channel_layouts_ref(layouts, &ctx->outputs[0]->in_channel_layouts);
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for (i = 0; i < ctx->nb_inputs; i++)
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ff_channel_layouts_ref(ff_all_channel_layouts(),
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&ctx->inputs[i]->out_channel_layouts);
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ff_set_common_formats (ctx, ff_planar_sample_fmts());
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ff_set_common_samplerates(ctx, ff_all_samplerates());
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static void guess_map_matching(AVFilterContext *ctx, ChannelMap *ch,
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for (i = 0; i < ctx->nb_inputs; i++) {
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AVFilterLink *link = ctx->inputs[i];
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if (ch->out_channel & link->channel_layout &&
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!(ch->out_channel & inputs[i])) {
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ch->in_channel = ch->out_channel;
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inputs[i] |= ch->out_channel;
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static void guess_map_any(AVFilterContext *ctx, ChannelMap *ch,
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for (i = 0; i < ctx->nb_inputs; i++) {
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AVFilterLink *link = ctx->inputs[i];
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if ((inputs[i] & link->channel_layout) != link->channel_layout) {
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uint64_t unused = link->channel_layout & ~inputs[i];
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ch->in_channel = av_channel_layout_extract_channel(unused, 0);
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inputs[i] |= ch->in_channel;
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static int join_config_output(AVFilterLink *outlink)
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AVFilterContext *ctx = outlink->src;
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JoinContext *s = ctx->priv;
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uint64_t *inputs; // nth element tracks which channels are used from nth input
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/* initialize inputs to user-specified mappings */
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if (!(inputs = av_mallocz(sizeof(*inputs) * ctx->nb_inputs)))
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return AVERROR(ENOMEM);
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for (i = 0; i < s->nb_channels; i++) {
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ChannelMap *ch = &s->channels[i];
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AVFilterLink *inlink;
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inlink = ctx->inputs[ch->input];
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ch->in_channel = av_channel_layout_extract_channel(inlink->channel_layout,
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if (!(ch->in_channel & inlink->channel_layout)) {
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av_log(ctx, AV_LOG_ERROR, "Requested channel %s is not present in "
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"input stream #%d.\n", av_get_channel_name(ch->in_channel),
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ret = AVERROR(EINVAL);
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inputs[ch->input] |= ch->in_channel;
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/* guess channel maps when not explicitly defined */
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/* first try unused matching channels */
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for (i = 0; i < s->nb_channels; i++) {
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ChannelMap *ch = &s->channels[i];
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guess_map_matching(ctx, ch, inputs);
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/* if the above failed, try to find _any_ unused input channel */
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for (i = 0; i < s->nb_channels; i++) {
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ChannelMap *ch = &s->channels[i];
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guess_map_any(ctx, ch, inputs);
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av_log(ctx, AV_LOG_ERROR, "Could not find input channel for "
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"output channel '%s'.\n",
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av_get_channel_name(ch->out_channel));
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ch->in_channel_idx = av_get_channel_layout_channel_index(ctx->inputs[ch->input]->channel_layout,
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av_log(ctx, AV_LOG_VERBOSE, "mappings: ");
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for (i = 0; i < s->nb_channels; i++) {
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ChannelMap *ch = &s->channels[i];
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av_log(ctx, AV_LOG_VERBOSE, "%d.%s => %s ", ch->input,
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av_get_channel_name(ch->in_channel),
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av_get_channel_name(ch->out_channel));
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av_log(ctx, AV_LOG_VERBOSE, "\n");
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for (i = 0; i < ctx->nb_inputs; i++) {
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av_log(ctx, AV_LOG_WARNING, "No channels are used from input "
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static void join_free_buffer(AVFilterBuffer *buf)
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JoinBufferPriv *priv = buf->priv;
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for (i = 0; i < priv->nb_in_buffers; i++)
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avfilter_unref_bufferp(&priv->in_buffers[i]);
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av_freep(&priv->in_buffers);
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av_freep(&buf->priv);
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if (buf->extended_data != buf->data)
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av_freep(&buf->extended_data);
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static int join_request_frame(AVFilterLink *outlink)
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AVFilterContext *ctx = outlink->src;
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JoinContext *s = ctx->priv;
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AVFilterBufferRef *buf;
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JoinBufferPriv *priv;
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int linesize = INT_MAX;
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/* get a frame on each input */
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for (i = 0; i < ctx->nb_inputs; i++) {
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AVFilterLink *inlink = ctx->inputs[i];
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if (!s->input_frames[i] &&
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(ret = ff_request_frame(inlink)) < 0)
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/* request the same number of samples on all inputs */
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nb_samples = s->input_frames[0]->audio->nb_samples;
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for (j = 1; !i && j < ctx->nb_inputs; j++)
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ctx->inputs[j]->request_samples = nb_samples;
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for (i = 0; i < s->nb_channels; i++) {
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ChannelMap *ch = &s->channels[i];
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AVFilterBufferRef *cur_buf = s->input_frames[ch->input];
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s->data[i] = cur_buf->extended_data[ch->in_channel_idx];
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linesize = FFMIN(linesize, cur_buf->linesize[0]);
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perms &= cur_buf->perms;
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av_assert0(nb_samples > 0);
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buf = avfilter_get_audio_buffer_ref_from_arrays(s->data, linesize, perms,
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nb_samples, outlink->format,
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outlink->channel_layout);
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return AVERROR(ENOMEM);
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buf->buf->free = join_free_buffer;
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buf->pts = s->input_frames[0]->pts;
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if (!(priv = av_mallocz(sizeof(*priv))))
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if (!(priv->in_buffers = av_mallocz(sizeof(*priv->in_buffers) * ctx->nb_inputs)))
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for (i = 0; i < ctx->nb_inputs; i++)
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priv->in_buffers[i] = s->input_frames[i];
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priv->nb_in_buffers = ctx->nb_inputs;
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buf->buf->priv = priv;
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ret = ff_filter_frame(outlink, buf);
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memset(s->input_frames, 0, sizeof(*s->input_frames) * ctx->nb_inputs);
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avfilter_unref_buffer(buf);
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av_freep(&priv->in_buffers);
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return AVERROR(ENOMEM);
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static const AVFilterPad avfilter_af_join_outputs[] = {
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.type = AVMEDIA_TYPE_AUDIO,
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.config_props = join_config_output,
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.request_frame = join_request_frame,
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AVFilter avfilter_af_join = {
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.description = NULL_IF_CONFIG_SMALL("Join multiple audio streams into "
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"multi-channel output"),
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.priv_size = sizeof(JoinContext),
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.uninit = join_uninit,
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.query_formats = join_query_formats,
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.outputs = avfilter_af_join_outputs,