avconv: multithreaded demuxing.

When there are multiple input files, run demuxing for each input file in
a separate thread, so reading packets does not block.

This is useful for achieving low latency when reading from multiple
(possibly slow) input streams.

avconv.c

@@ -69,6 +69,14 @@
 #include <sys/select.h>
 #endif
 
+#if HAVE_THREADS
+#if HAVE_PTHREADS
+#include <pthread.h>
+#else
+#include "libavcodec/w32pthreads.h"
+#endif
+#endif
+
 #include <time.h>
 
 #include "cmdutils.h"
@@ -140,6 +148,11 @@ static float dts_delta_threshold = 10;
 
 static int print_stats = 1;
 
+#if HAVE_THREADS
+/* signal to input threads that they should exit; set by the main thread */
+static int transcoding_finished;
+#endif
+
 #define DEFAULT_PASS_LOGFILENAME_PREFIX "av2pass"
 
 typedef struct InputFilter {
@@ -219,6 +232,15 @@ typedef struct InputFile {
     int nb_streams;       /* number of stream that avconv is aware of; may be different
                              from ctx.nb_streams if new streams appear during av_read_frame() */
     int rate_emu;
+
+#if HAVE_THREADS
+    pthread_t thread;           /* thread reading from this file */
+    int finished;               /* the thread has exited */
+    int joined;                 /* the thread has been joined */
+    pthread_mutex_t fifo_lock;  /* lock for access to fifo */
+    pthread_cond_t  fifo_cond;  /* the main thread will signal on this cond after reading from fifo */
+    AVFifoBuffer *fifo;         /* demuxed packets are stored here; freed by the main thread */
+#endif
 } InputFile;
 
 typedef struct OutputStream {
@@ -2765,6 +2787,125 @@ static int select_input_file(uint8_t *no_packet)
     return file_index;
 }
 
+#if HAVE_THREADS
+static void *input_thread(void *arg)
+{
+    InputFile *f = arg;
+    int ret = 0;
+
+    while (!transcoding_finished && ret >= 0) {
+        AVPacket pkt;
+        ret = av_read_frame(f->ctx, &pkt);
+
+        if (ret == AVERROR(EAGAIN)) {
+            usleep(10000);
+            ret = 0;
+            continue;
+        } else if (ret < 0)
+            break;
+
+        pthread_mutex_lock(&f->fifo_lock);
+        while (!av_fifo_space(f->fifo))
+            pthread_cond_wait(&f->fifo_cond, &f->fifo_lock);
+
+        av_dup_packet(&pkt);
+        av_fifo_generic_write(f->fifo, &pkt, sizeof(pkt), NULL);
+
+        pthread_mutex_unlock(&f->fifo_lock);
+    }
+
+    f->finished = 1;
+    return NULL;
+}
+
+static void free_input_threads(void)
+{
+    int i;
+
+    if (nb_input_files == 1)
+        return;
+
+    transcoding_finished = 1;
+
+    for (i = 0; i < nb_input_files; i++) {
+        InputFile *f = input_files[i];
+        AVPacket pkt;
+
+        if (f->joined)
+            continue;
+
+        pthread_mutex_lock(&f->fifo_lock);
+        while (av_fifo_size(f->fifo)) {
+            av_fifo_generic_read(f->fifo, &pkt, sizeof(pkt), NULL);
+            av_free_packet(&pkt);
+        }
+        pthread_cond_signal(&f->fifo_cond);
+        pthread_mutex_unlock(&f->fifo_lock);
+
+        pthread_join(f->thread, NULL);
+        f->joined = 1;
+
+        while (av_fifo_size(f->fifo)) {
+            av_fifo_generic_read(f->fifo, &pkt, sizeof(pkt), NULL);
+            av_free_packet(&pkt);
+        }
+        av_fifo_free(f->fifo);
+    }
+}
+
+static int init_input_threads(void)
+{
+    int i, ret;
+
+    if (nb_input_files == 1)
+        return 0;
+
+    for (i = 0; i < nb_input_files; i++) {
+        InputFile *f = input_files[i];
+
+        if (!(f->fifo = av_fifo_alloc(8*sizeof(AVPacket))))
+            return AVERROR(ENOMEM);
+
+        pthread_mutex_init(&f->fifo_lock, NULL);
+        pthread_cond_init (&f->fifo_cond, NULL);
+
+        if ((ret = pthread_create(&f->thread, NULL, input_thread, f)))
+            return AVERROR(ret);
+    }
+    return 0;
+}
+
+static int get_input_packet_mt(InputFile *f, AVPacket *pkt)
+{
+    int ret = 0;
+
+    pthread_mutex_lock(&f->fifo_lock);
+
+    if (av_fifo_size(f->fifo)) {
+        av_fifo_generic_read(f->fifo, pkt, sizeof(*pkt), NULL);
+        pthread_cond_signal(&f->fifo_cond);
+    } else {
+        if (f->finished)
+            ret = AVERROR_EOF;
+        else
+            ret = AVERROR(EAGAIN);
+    }
+
+    pthread_mutex_unlock(&f->fifo_lock);
+
+    return ret;
+}
+#endif
+
+static int get_input_packet(InputFile *f, AVPacket *pkt)
+{
+#if HAVE_THREADS
+    if (nb_input_files > 1)
+        return get_input_packet_mt(f, pkt);
+#endif
+    return av_read_frame(f->ctx, pkt);
+}
+
 /*
  * The following code is the main loop of the file converter
  */
@@ -2790,6 +2931,11 @@ static int transcode(void)
 
     timer_start = av_gettime();
 
+#if HAVE_THREADS
+    if ((ret = init_input_threads()) < 0)
+        goto fail;
+#endif
+
     for (; received_sigterm == 0;) {
         int file_index, ist_index;
         AVPacket pkt;
@@ -2810,12 +2956,13 @@ static int transcode(void)
                 usleep(10000);
                 continue;
             }
+            av_log(NULL, AV_LOG_VERBOSE, "No more inputs to read from, finishing.\n");
             break;
         }
 
-        /* read a frame from it and output it in the fifo */
         is  = input_files[file_index]->ctx;
-        ret = av_read_frame(is, &pkt);
+        ret = get_input_packet(input_files[file_index], &pkt);
+
         if (ret == AVERROR(EAGAIN)) {
             no_packet[file_index] = 1;
             no_packet_count++;
@@ -2897,6 +3044,9 @@ static int transcode(void)
         /* dump report by using the output first video and audio streams */
         print_report(0, timer_start);
     }
+#if HAVE_THREADS
+    free_input_threads();
+#endif
 
     /* at the end of stream, we must flush the decoder buffers */
     for (i = 0; i < nb_input_streams; i++) {
@@ -2941,6 +3091,9 @@ static int transcode(void)
 
  fail:
     av_freep(&no_packet);
+#if HAVE_THREADS
+    free_input_threads();
+#endif
 
     if (output_streams) {
         for (i = 0; i < nb_output_streams; i++) {