libavcodec/frame_thread_encoder.c - third_party/ffmpeg - Git at Google

 /*
  * Copyright (c) 2012 Michael Niedermayer <michaelni@gmx.at>
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */

 #include <stdatomic.h>

 #include "frame_thread_encoder.h"

 #include "libavutil/avassert.h"
 #include "libavutil/cpu.h"
 #include "libavutil/mem.h"
 #include "libavutil/opt.h"
 #include "libavutil/thread.h"
 #include "avcodec.h"
 #include "avcodec_internal.h"
 #include "codec_par.h"
 #include "encode.h"
 #include "internal.h"
 #include "pthread_internal.h"

 #define MAX_THREADS 64
 /* There can be as many as MAX_THREADS + 1 outstanding tasks.
  * An additional + 1 is needed so that one can distinguish
  * the case of zero and MAX_THREADS + 1 outstanding tasks modulo
  * the number of buffers. */
 #define BUFFER_SIZE (MAX_THREADS + 2)

 typedef struct{
     AVFrame  *indata;
     AVPacket *outdata;
     int       return_code;
     int       finished;
     int       got_packet;
 } Task;

 typedef struct{
     AVCodecContext *parent_avctx;

     pthread_mutex_t task_fifo_mutex; /* Used to guard (next_)task_index */
     pthread_cond_t task_fifo_cond;

     unsigned pthread_init_cnt;
     unsigned max_tasks;
     Task tasks[BUFFER_SIZE];
     pthread_mutex_t finished_task_mutex; /* Guards tasks[i].finished */
     pthread_cond_t finished_task_cond;

     unsigned next_task_index;
     unsigned task_index;
     unsigned finished_task_index;

     pthread_t worker[MAX_THREADS];
     atomic_int exit;
 } ThreadContext;

 #define OFF(member) offsetof(ThreadContext, member)
 DEFINE_OFFSET_ARRAY(ThreadContext, thread_ctx, pthread_init_cnt,
                     (OFF(task_fifo_mutex), OFF(finished_task_mutex)),
                     (OFF(task_fifo_cond),  OFF(finished_task_cond)));
 #undef OFF

 static void * attribute_align_arg worker(void *v){
     AVCodecContext *avctx = v;
     ThreadContext *c = avctx->internal->frame_thread_encoder;

     while (!atomic_load(&c->exit)) {
         int ret;
         AVPacket *pkt;
         AVFrame *frame;
         Task *task;
         unsigned task_index;

         pthread_mutex_lock(&c->task_fifo_mutex);
         while (c->next_task_index == c->task_index || atomic_load(&c->exit)) {
             if (atomic_load(&c->exit)) {
                 pthread_mutex_unlock(&c->task_fifo_mutex);
                 goto end;
             }
             pthread_cond_wait(&c->task_fifo_cond, &c->task_fifo_mutex);
         }
         task_index         = c->next_task_index;
         c->next_task_index = (c->next_task_index + 1) % c->max_tasks;
         pthread_mutex_unlock(&c->task_fifo_mutex);
         /* The main thread ensures that any two outstanding tasks have
          * different indices, ergo each worker thread owns its element
          * of c->tasks with the exception of finished, which is shared
          * with the main thread and guarded by finished_task_mutex. */
         task  = &c->tasks[task_index];
         frame = task->indata;
         pkt   = task->outdata;

         ret = ff_encode_encode_cb(avctx, pkt, frame, &task->got_packet);
         pthread_mutex_lock(&c->finished_task_mutex);
         task->return_code = ret;
         task->finished    = 1;
         pthread_cond_signal(&c->finished_task_cond);
         pthread_mutex_unlock(&c->finished_task_mutex);
     }
 end:
     avcodec_free_context(&avctx);
     return NULL;
 }

 av_cold int ff_frame_thread_encoder_init(AVCodecContext *avctx)
 {
     int i=0;
     ThreadContext *c;
     AVCodecContext *thread_avctx = NULL;
     AVCodecParameters *par = NULL;
     int ret;

     if(   !(avctx->thread_type & FF_THREAD_FRAME)
        || !(avctx->codec->capabilities & AV_CODEC_CAP_FRAME_THREADS))
         return 0;

     if(   !avctx->thread_count
        && avctx->codec_id == AV_CODEC_ID_MJPEG
        && !(avctx->flags & AV_CODEC_FLAG_QSCALE)) {
         av_log(avctx, AV_LOG_DEBUG,
                "Forcing thread count to 1 for MJPEG encoding, use -thread_type slice "
                "or a constant quantizer if you want to use multiple cpu cores\n");
         avctx->thread_count = 1;
     }
     if(   avctx->thread_count > 1
        && avctx->codec_id == AV_CODEC_ID_MJPEG
        && !(avctx->flags & AV_CODEC_FLAG_QSCALE))
         av_log(avctx, AV_LOG_WARNING,
                "MJPEG CBR encoding works badly with frame multi-threading, consider "
                "using -threads 1, -thread_type slice or a constant quantizer.\n");

     if (avctx->codec_id == AV_CODEC_ID_HUFFYUV ||
         avctx->codec_id == AV_CODEC_ID_FFVHUFF) {
         int warn = 0;
         int64_t tmp;

         if (avctx->flags & AV_CODEC_FLAG_PASS1)
             warn = 1;
         else if (av_opt_get_int(avctx->priv_data, "context", 0, &tmp) >= 0 &&
                  tmp > 0) {
             warn = av_opt_get_int(avctx->priv_data, "non_deterministic", 0, &tmp) < 0
                    || !tmp;
         }
         // huffyuv does not support these with multiple frame threads currently
         if (warn) {
             av_log(avctx, AV_LOG_WARNING,
                "Forcing thread count to 1 for huffyuv encoding with first pass or context 1\n");
             avctx->thread_count = 1;
         }
     }

     if(!avctx->thread_count) {
         avctx->thread_count = av_cpu_count();
         avctx->thread_count = FFMIN(avctx->thread_count, MAX_THREADS);
     }

     if(avctx->thread_count <= 1)
         return 0;

     if(avctx->thread_count > MAX_THREADS)
         return AVERROR(EINVAL);

     av_assert0(!avctx->internal->frame_thread_encoder);
     c = avctx->internal->frame_thread_encoder = av_mallocz(sizeof(ThreadContext));
     if(!c)
         return AVERROR(ENOMEM);

     c->parent_avctx = avctx;

     ret = ff_pthread_init(c, thread_ctx_offsets);
     if (ret < 0)
         goto fail;
     atomic_init(&c->exit, 0);

     c->max_tasks = avctx->thread_count + 2;
     for (unsigned j = 0; j < c->max_tasks; j++) {
         if (!(c->tasks[j].indata  = av_frame_alloc()) ||
             !(c->tasks[j].outdata = av_packet_alloc())) {
             ret = AVERROR(ENOMEM);
             goto fail;
         }
     }

     par = avcodec_parameters_alloc();
     if (!par) {
         ret = AVERROR(ENOMEM);
         goto fail;
     }

     ret = avcodec_parameters_from_context(par, avctx);
     if (ret < 0)
         goto fail;

     for(i=0; i<avctx->thread_count ; i++){
         thread_avctx = avcodec_alloc_context3(avctx->codec);
         if (!thread_avctx) {
             ret = AVERROR(ENOMEM);
             goto fail;
         }

         ret = avcodec_parameters_to_context(thread_avctx, par);
         if (ret < 0)
             goto fail;

         ret = av_opt_copy(thread_avctx, avctx);
         if (ret < 0)
             goto fail;
         if (avctx->codec->priv_class) {
             ret = av_opt_copy(thread_avctx->priv_data, avctx->priv_data);
             if (ret < 0)
                 goto fail;
         }
         thread_avctx->thread_count = 1;
         thread_avctx->active_thread_type &= ~FF_THREAD_FRAME;

 #define DUP_MATRIX(m)                                                       \
         if (avctx->m) {                                                     \
             thread_avctx->m = av_memdup(avctx->m, 64 * sizeof(*avctx->m));  \
             if (!thread_avctx->m) {                                         \
                 ret = AVERROR(ENOMEM);                                      \
                 goto fail;                                                  \
             }                                                               \
         }
         DUP_MATRIX(intra_matrix);
         DUP_MATRIX(chroma_intra_matrix);
         DUP_MATRIX(inter_matrix);

 #undef DUP_MATRIX

         thread_avctx->opaque            = avctx->opaque;
         thread_avctx->get_encode_buffer = avctx->get_encode_buffer;
         thread_avctx->execute           = avctx->execute;
         thread_avctx->execute2          = avctx->execute2;
         thread_avctx->stats_in          = avctx->stats_in;

         if ((ret = avcodec_open2(thread_avctx, avctx->codec, NULL)) < 0)
             goto fail;
         av_assert0(!thread_avctx->internal->frame_thread_encoder);
         thread_avctx->internal->frame_thread_encoder = c;
         if ((ret = pthread_create(&c->worker[i], NULL, worker, thread_avctx))) {
             ret = AVERROR(ret);
             goto fail;
         }
     }

     avcodec_parameters_free(&par);

     avctx->active_thread_type = FF_THREAD_FRAME;

     return 0;
 fail:
     avcodec_parameters_free(&par);
     avcodec_free_context(&thread_avctx);
     avctx->thread_count = i;
     av_log(avctx, AV_LOG_ERROR, "ff_frame_thread_encoder_init failed\n");
     ff_frame_thread_encoder_free(avctx);
     return ret;
 }

 av_cold void ff_frame_thread_encoder_free(AVCodecContext *avctx)
 {
     ThreadContext *c= avctx->internal->frame_thread_encoder;

     /* In case initializing the mutexes/condition variables failed,
      * they must not be used. In this case the thread_count is zero
      * as no thread has been initialized yet. */
     if (avctx->thread_count > 0) {
         pthread_mutex_lock(&c->task_fifo_mutex);
         atomic_store(&c->exit, 1);
         pthread_cond_broadcast(&c->task_fifo_cond);
         pthread_mutex_unlock(&c->task_fifo_mutex);

         for (int i = 0; i < avctx->thread_count; i++)
             pthread_join(c->worker[i], NULL);
     }

     for (unsigned i = 0; i < c->max_tasks; i++) {
         av_frame_free(&c->tasks[i].indata);
         av_packet_free(&c->tasks[i].outdata);
     }

     ff_pthread_free(c, thread_ctx_offsets);
     av_freep(&avctx->internal->frame_thread_encoder);
 }

 int ff_thread_video_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
                                  AVFrame *frame, int *got_packet_ptr)
 {
     ThreadContext *c = avctx->internal->frame_thread_encoder;
     Task *outtask;

     av_assert1(!*got_packet_ptr);

     if(frame){
         av_frame_move_ref(c->tasks[c->task_index].indata, frame);

         pthread_mutex_lock(&c->task_fifo_mutex);
         c->task_index = (c->task_index + 1) % c->max_tasks;
         pthread_cond_signal(&c->task_fifo_cond);
         pthread_mutex_unlock(&c->task_fifo_mutex);
     }

     outtask = &c->tasks[c->finished_task_index];
     pthread_mutex_lock(&c->finished_task_mutex);
     /* The access to task_index in the following code is ok,
      * because it is only ever changed by the main thread. */
     if (c->task_index == c->finished_task_index ||
         (frame && !outtask->finished &&
          (c->task_index - c->finished_task_index + c->max_tasks) % c->max_tasks <= avctx->thread_count)) {
             pthread_mutex_unlock(&c->finished_task_mutex);
             return 0;
         }
     while (!outtask->finished) {
         pthread_cond_wait(&c->finished_task_cond, &c->finished_task_mutex);
     }
     pthread_mutex_unlock(&c->finished_task_mutex);
     /* We now own outtask completely: No worker thread touches it any more,
      * because there is no outstanding task with this index. */
     outtask->finished = 0;
     av_packet_move_ref(pkt, outtask->outdata);
     *got_packet_ptr = outtask->got_packet;
     c->finished_task_index = (c->finished_task_index + 1) % c->max_tasks;

     return outtask->return_code;
 }
	/*
	* Copyright (c) 2012 Michael Niedermayer <michaelni@gmx.at>
	*
	* This file is part of FFmpeg.
	*
	* FFmpeg is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* FFmpeg is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with FFmpeg; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	#include <stdatomic.h>

	#include "frame_thread_encoder.h"

	#include "libavutil/avassert.h"
	#include "libavutil/cpu.h"
	#include "libavutil/mem.h"
	#include "libavutil/opt.h"
	#include "libavutil/thread.h"
	#include "avcodec.h"
	#include "avcodec_internal.h"
	#include "codec_par.h"
	#include "encode.h"
	#include "internal.h"
	#include "pthread_internal.h"

	#define MAX_THREADS 64
	/* There can be as many as MAX_THREADS + 1 outstanding tasks.
	* An additional + 1 is needed so that one can distinguish
	* the case of zero and MAX_THREADS + 1 outstanding tasks modulo
	* the number of buffers. */
	#define BUFFER_SIZE (MAX_THREADS + 2)

	typedef struct{
	AVFrame *indata;
	AVPacket *outdata;
	int return_code;
	int finished;
	int got_packet;
	} Task;

	typedef struct{
	AVCodecContext *parent_avctx;

	pthread_mutex_t task_fifo_mutex; /* Used to guard (next_)task_index */
	pthread_cond_t task_fifo_cond;

	unsigned pthread_init_cnt;
	unsigned max_tasks;
	Task tasks[BUFFER_SIZE];
	pthread_mutex_t finished_task_mutex; /* Guards tasks[i].finished */
	pthread_cond_t finished_task_cond;

	unsigned next_task_index;
	unsigned task_index;
	unsigned finished_task_index;

	pthread_t worker[MAX_THREADS];
	atomic_int exit;
	} ThreadContext;

	#define OFF(member) offsetof(ThreadContext, member)
	DEFINE_OFFSET_ARRAY(ThreadContext, thread_ctx, pthread_init_cnt,
	(OFF(task_fifo_mutex), OFF(finished_task_mutex)),
	(OFF(task_fifo_cond), OFF(finished_task_cond)));
	#undef OFF

	static void * attribute_align_arg worker(void *v){
	AVCodecContext *avctx = v;
	ThreadContext *c = avctx->internal->frame_thread_encoder;

	while (!atomic_load(&c->exit)) {
	int ret;
	AVPacket *pkt;
	AVFrame *frame;
	Task *task;
	unsigned task_index;

	pthread_mutex_lock(&c->task_fifo_mutex);
	while (c->next_task_index == c->task_index \|\| atomic_load(&c->exit)) {
	if (atomic_load(&c->exit)) {
	pthread_mutex_unlock(&c->task_fifo_mutex);
	goto end;
	}
	pthread_cond_wait(&c->task_fifo_cond, &c->task_fifo_mutex);
	}
	task_index = c->next_task_index;
	c->next_task_index = (c->next_task_index + 1) % c->max_tasks;
	pthread_mutex_unlock(&c->task_fifo_mutex);
	/* The main thread ensures that any two outstanding tasks have
	* different indices, ergo each worker thread owns its element
	* of c->tasks with the exception of finished, which is shared
	* with the main thread and guarded by finished_task_mutex. */
	task = &c->tasks[task_index];
	frame = task->indata;
	pkt = task->outdata;

	ret = ff_encode_encode_cb(avctx, pkt, frame, &task->got_packet);
	pthread_mutex_lock(&c->finished_task_mutex);
	task->return_code = ret;
	task->finished = 1;
	pthread_cond_signal(&c->finished_task_cond);
	pthread_mutex_unlock(&c->finished_task_mutex);
	}
	end:
	avcodec_free_context(&avctx);
	return NULL;
	}

	av_cold int ff_frame_thread_encoder_init(AVCodecContext *avctx)
	{
	int i=0;
	ThreadContext *c;
	AVCodecContext *thread_avctx = NULL;
	AVCodecParameters *par = NULL;
	int ret;

	if( !(avctx->thread_type & FF_THREAD_FRAME)
	\|\| !(avctx->codec->capabilities & AV_CODEC_CAP_FRAME_THREADS))
	return 0;

	if( !avctx->thread_count
	&& avctx->codec_id == AV_CODEC_ID_MJPEG
	&& !(avctx->flags & AV_CODEC_FLAG_QSCALE)) {
	av_log(avctx, AV_LOG_DEBUG,
	"Forcing thread count to 1 for MJPEG encoding, use -thread_type slice "
	"or a constant quantizer if you want to use multiple cpu cores\n");
	avctx->thread_count = 1;
	}
	if( avctx->thread_count > 1
	&& avctx->codec_id == AV_CODEC_ID_MJPEG
	&& !(avctx->flags & AV_CODEC_FLAG_QSCALE))
	av_log(avctx, AV_LOG_WARNING,
	"MJPEG CBR encoding works badly with frame multi-threading, consider "
	"using -threads 1, -thread_type slice or a constant quantizer.\n");

	if (avctx->codec_id == AV_CODEC_ID_HUFFYUV \|\|
	avctx->codec_id == AV_CODEC_ID_FFVHUFF) {
	int warn = 0;
	int64_t tmp;

	if (avctx->flags & AV_CODEC_FLAG_PASS1)
	warn = 1;
	else if (av_opt_get_int(avctx->priv_data, "context", 0, &tmp) >= 0 &&
	tmp > 0) {
	warn = av_opt_get_int(avctx->priv_data, "non_deterministic", 0, &tmp) < 0
	\|\| !tmp;
	}
	// huffyuv does not support these with multiple frame threads currently
	if (warn) {
	av_log(avctx, AV_LOG_WARNING,
	"Forcing thread count to 1 for huffyuv encoding with first pass or context 1\n");
	avctx->thread_count = 1;
	}
	}

	if(!avctx->thread_count) {
	avctx->thread_count = av_cpu_count();
	avctx->thread_count = FFMIN(avctx->thread_count, MAX_THREADS);
	}

	if(avctx->thread_count <= 1)
	return 0;

	if(avctx->thread_count > MAX_THREADS)
	return AVERROR(EINVAL);

	av_assert0(!avctx->internal->frame_thread_encoder);
	c = avctx->internal->frame_thread_encoder = av_mallocz(sizeof(ThreadContext));
	if(!c)
	return AVERROR(ENOMEM);

	c->parent_avctx = avctx;

	ret = ff_pthread_init(c, thread_ctx_offsets);
	if (ret < 0)
	goto fail;
	atomic_init(&c->exit, 0);

	c->max_tasks = avctx->thread_count + 2;
	for (unsigned j = 0; j < c->max_tasks; j++) {
	if (!(c->tasks[j].indata = av_frame_alloc()) \|\|
	!(c->tasks[j].outdata = av_packet_alloc())) {
	ret = AVERROR(ENOMEM);
	goto fail;
	}
	}

	par = avcodec_parameters_alloc();
	if (!par) {
	ret = AVERROR(ENOMEM);
	goto fail;
	}

	ret = avcodec_parameters_from_context(par, avctx);
	if (ret < 0)
	goto fail;

	for(i=0; i<avctx->thread_count ; i++){
	thread_avctx = avcodec_alloc_context3(avctx->codec);
	if (!thread_avctx) {
	ret = AVERROR(ENOMEM);
	goto fail;
	}

	ret = avcodec_parameters_to_context(thread_avctx, par);
	if (ret < 0)
	goto fail;

	ret = av_opt_copy(thread_avctx, avctx);
	if (ret < 0)
	goto fail;
	if (avctx->codec->priv_class) {
	ret = av_opt_copy(thread_avctx->priv_data, avctx->priv_data);
	if (ret < 0)
	goto fail;
	}
	thread_avctx->thread_count = 1;
	thread_avctx->active_thread_type &= ~FF_THREAD_FRAME;

	#define DUP_MATRIX(m) \
	if (avctx->m) { \
	thread_avctx->m = av_memdup(avctx->m, 64 * sizeof(*avctx->m)); \
	if (!thread_avctx->m) { \
	ret = AVERROR(ENOMEM); \
	goto fail; \
	} \
	}
	DUP_MATRIX(intra_matrix);
	DUP_MATRIX(chroma_intra_matrix);
	DUP_MATRIX(inter_matrix);

	#undef DUP_MATRIX

	thread_avctx->opaque = avctx->opaque;
	thread_avctx->get_encode_buffer = avctx->get_encode_buffer;
	thread_avctx->execute = avctx->execute;
	thread_avctx->execute2 = avctx->execute2;
	thread_avctx->stats_in = avctx->stats_in;

	if ((ret = avcodec_open2(thread_avctx, avctx->codec, NULL)) < 0)
	goto fail;
	av_assert0(!thread_avctx->internal->frame_thread_encoder);
	thread_avctx->internal->frame_thread_encoder = c;
	if ((ret = pthread_create(&c->worker[i], NULL, worker, thread_avctx))) {
	ret = AVERROR(ret);
	goto fail;
	}
	}

	avcodec_parameters_free(&par);

	avctx->active_thread_type = FF_THREAD_FRAME;

	return 0;
	fail:
	avcodec_parameters_free(&par);
	avcodec_free_context(&thread_avctx);
	avctx->thread_count = i;
	av_log(avctx, AV_LOG_ERROR, "ff_frame_thread_encoder_init failed\n");
	ff_frame_thread_encoder_free(avctx);
	return ret;
	}

	av_cold void ff_frame_thread_encoder_free(AVCodecContext *avctx)
	{
	ThreadContext *c= avctx->internal->frame_thread_encoder;

	/* In case initializing the mutexes/condition variables failed,
	* they must not be used. In this case the thread_count is zero
	* as no thread has been initialized yet. */
	if (avctx->thread_count > 0) {
	pthread_mutex_lock(&c->task_fifo_mutex);
	atomic_store(&c->exit, 1);
	pthread_cond_broadcast(&c->task_fifo_cond);
	pthread_mutex_unlock(&c->task_fifo_mutex);

	for (int i = 0; i < avctx->thread_count; i++)
	pthread_join(c->worker[i], NULL);
	}

	for (unsigned i = 0; i < c->max_tasks; i++) {
	av_frame_free(&c->tasks[i].indata);
	av_packet_free(&c->tasks[i].outdata);
	}

	ff_pthread_free(c, thread_ctx_offsets);
	av_freep(&avctx->internal->frame_thread_encoder);
	}

	int ff_thread_video_encode_frame(AVCodecContext avctx, AVPacket pkt,
	AVFrame frame, int got_packet_ptr)
	{
	ThreadContext *c = avctx->internal->frame_thread_encoder;
	Task *outtask;

	av_assert1(!*got_packet_ptr);

	if(frame){
	av_frame_move_ref(c->tasks[c->task_index].indata, frame);

	pthread_mutex_lock(&c->task_fifo_mutex);
	c->task_index = (c->task_index + 1) % c->max_tasks;
	pthread_cond_signal(&c->task_fifo_cond);
	pthread_mutex_unlock(&c->task_fifo_mutex);
	}

	outtask = &c->tasks[c->finished_task_index];
	pthread_mutex_lock(&c->finished_task_mutex);
	/* The access to task_index in the following code is ok,
	* because it is only ever changed by the main thread. */
	if (c->task_index == c->finished_task_index \|\|
	(frame && !outtask->finished &&
	(c->task_index - c->finished_task_index + c->max_tasks) % c->max_tasks <= avctx->thread_count)) {
	pthread_mutex_unlock(&c->finished_task_mutex);
	return 0;
	}
	while (!outtask->finished) {
	pthread_cond_wait(&c->finished_task_cond, &c->finished_task_mutex);
	}
	pthread_mutex_unlock(&c->finished_task_mutex);
	/* We now own outtask completely: No worker thread touches it any more,
	* because there is no outstanding task with this index. */
	outtask->finished = 0;
	av_packet_move_ref(pkt, outtask->outdata);
	*got_packet_ptr = outtask->got_packet;
	c->finished_task_index = (c->finished_task_index + 1) % c->max_tasks;

	return outtask->return_code;
	}