avcodec/mediacodecdec: restructure mediacodec_receive_frame

The new logic follows a recommendation by @rcombs to use
dequeueInputBuffer with a timeout of 0 as a way to detect
whether the codec wants more data. The dequeued buffer index is
kept in MediaCodecDecContext until it can be used next.

A similar technique is also used by the Google's official media
player Exoplayer: see MediaCodecRenderer.feedInputBuffer().
Signed-off-by: Aman Gupta <aman@tmm1.net>
Signed-off-by: Matthieu Bouron <matthieu.bouron@gmail.com>

libavcodec/mediacodecdec.c

@@ -391,33 +391,11 @@ done:
     return ret;
 }
 
-static int mediacodec_send_receive(AVCodecContext *avctx,
-                                   MediaCodecH264DecContext *s,
-                                   AVFrame *frame, bool wait)
-{
-    int ret;
-
-    /* send any pending data from buffered packet */
-    while (s->buffered_pkt.size) {
-        ret = ff_mediacodec_dec_send(avctx, s->ctx, &s->buffered_pkt);
-        if (ret == AVERROR(EAGAIN))
-            break;
-        else if (ret < 0)
-            return ret;
-        s->buffered_pkt.size -= ret;
-        s->buffered_pkt.data += ret;
-        if (s->buffered_pkt.size <= 0)
-            av_packet_unref(&s->buffered_pkt);
-    }
-
-    /* check for new frame */
-    return ff_mediacodec_dec_receive(avctx, s->ctx, frame, wait);
-}
-
 static int mediacodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
 {
     MediaCodecH264DecContext *s = avctx->priv_data;
     int ret;
+    ssize_t index;
 
     /* In delay_flush mode, wait until the user has released or rendered
        all retained frames. */
@@ -427,28 +405,54 @@ static int mediacodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
         }
     }
 
-    /* flush buffered packet and check for new frame */
-    ret = mediacodec_send_receive(avctx, s, frame, false);
+    /* poll for new frame */
+    ret = ff_mediacodec_dec_receive(avctx, s->ctx, frame, false);
     if (ret != AVERROR(EAGAIN))
         return ret;
 
-    /* skip fetching new packet if we still have one buffered */
-    if (s->buffered_pkt.size > 0)
-        return mediacodec_send_receive(avctx, s, frame, true);
+    /* feed decoder */
+    while (1) {
+        if (s->ctx->current_input_buffer < 0) {
+            /* poll for input space */
+            index = ff_AMediaCodec_dequeueInputBuffer(s->ctx->codec, 0);
+            if (index < 0) {
+                /* no space, block for an output frame to appear */
+                return ff_mediacodec_dec_receive(avctx, s->ctx, frame, true);
+            }
+            s->ctx->current_input_buffer = index;
+        }
 
-    /* fetch new packet or eof */
-    ret = ff_decode_get_packet(avctx, &s->buffered_pkt);
-    if (ret == AVERROR_EOF) {
-        AVPacket null_pkt = { 0 };
-        ret = ff_mediacodec_dec_send(avctx, s->ctx, &null_pkt);
-        if (ret < 0)
+        /* try to flush any buffered packet data */
+        if (s->buffered_pkt.size > 0) {
+            ret = ff_mediacodec_dec_send(avctx, s->ctx, &s->buffered_pkt, false);
+            if (ret >= 0) {
+                s->buffered_pkt.size -= ret;
+                s->buffered_pkt.data += ret;
+                if (s->buffered_pkt.size <= 0)
+                    av_packet_unref(&s->buffered_pkt);
+            } else if (ret < 0 && ret != AVERROR(EAGAIN)) {
+                return ret;
+            }
+
+            /* poll for space again */
+            continue;
+        }
+
+        /* fetch new packet or eof */
+        ret = ff_decode_get_packet(avctx, &s->buffered_pkt);
+        if (ret == AVERROR_EOF) {
+            AVPacket null_pkt = { 0 };
+            ret = ff_mediacodec_dec_send(avctx, s->ctx, &null_pkt, true);
+            if (ret < 0)
+                return ret;
+        } else if (ret == AVERROR(EAGAIN) && s->ctx->current_input_buffer < 0) {
+            return ff_mediacodec_dec_receive(avctx, s->ctx, frame, true);
+        } else if (ret < 0) {
             return ret;
+        }
     }
-    else if (ret < 0)
-        return ret;
 
-    /* crank decoder with new packet */
-    return mediacodec_send_receive(avctx, s, frame, true);
+    return AVERROR(EAGAIN);
 }
 
 static void mediacodec_decode_flush(AVCodecContext *avctx)

libavcodec/mediacodecdec_common.c

@@ -450,6 +450,7 @@ static int mediacodec_dec_flush_codec(AVCodecContext *avctx, MediaCodecDecContex
     s->eos = 0;
     atomic_fetch_add(&s->serial, 1);
     atomic_init(&s->hw_buffer_count, 0);
+    s->current_input_buffer = -1;
 
     status = ff_AMediaCodec_flush(codec);
     if (status < 0) {
@@ -477,6 +478,7 @@ int ff_mediacodec_dec_init(AVCodecContext *avctx, MediaCodecDecContext *s,
     atomic_init(&s->refcount, 1);
     atomic_init(&s->hw_buffer_count, 0);
     atomic_init(&s->serial, 1);
+    s->current_input_buffer = -1;
 
     pix_fmt = ff_get_format(avctx, pix_fmts);
     if (pix_fmt == AV_PIX_FMT_MEDIACODEC) {
@@ -561,16 +563,16 @@ fail:
 }
 
 int ff_mediacodec_dec_send(AVCodecContext *avctx, MediaCodecDecContext *s,
-                           AVPacket *pkt)
+                           AVPacket *pkt, bool wait)
 {
     int offset = 0;
     int need_draining = 0;
     uint8_t *data;
-    ssize_t index;
+    ssize_t index = s->current_input_buffer;
     size_t size;
     FFAMediaCodec *codec = s->codec;
     int status;
-    int64_t input_dequeue_timeout_us = INPUT_DEQUEUE_TIMEOUT_US;
+    int64_t input_dequeue_timeout_us = wait ? INPUT_DEQUEUE_TIMEOUT_US : 0;
     int64_t pts;
 
     if (s->flushing) {
@@ -588,17 +590,19 @@ int ff_mediacodec_dec_send(AVCodecContext *avctx, MediaCodecDecContext *s,
     }
 
     while (offset < pkt->size || (need_draining && !s->draining)) {
-
-        index = ff_AMediaCodec_dequeueInputBuffer(codec, input_dequeue_timeout_us);
-        if (ff_AMediaCodec_infoTryAgainLater(codec, index)) {
-            av_log(avctx, AV_LOG_TRACE, "No input buffer available, try again later\n");
-            break;
-        }
-
         if (index < 0) {
-            av_log(avctx, AV_LOG_ERROR, "Failed to dequeue input buffer (status=%zd)\n", index);
-            return AVERROR_EXTERNAL;
+            index = ff_AMediaCodec_dequeueInputBuffer(codec, input_dequeue_timeout_us);
+            if (ff_AMediaCodec_infoTryAgainLater(codec, index)) {
+                av_log(avctx, AV_LOG_TRACE, "No input buffer available, try again later\n");
+                break;
+            }
+
+            if (index < 0) {
+                av_log(avctx, AV_LOG_ERROR, "Failed to dequeue input buffer (status=%zd)\n", index);
+                return AVERROR_EXTERNAL;
+            }
         }
+        s->current_input_buffer = -1;
 
         data = ff_AMediaCodec_getInputBuffer(codec, index, &size);
         if (!data) {

libavcodec/mediacodecdec_common.h

@@ -65,6 +65,7 @@ typedef struct MediaCodecDecContext {
     int display_height;
 
     uint64_t output_buffer_count;
+    ssize_t current_input_buffer;
 
     bool delay_flush;
     atomic_int serial;
@@ -78,7 +79,8 @@ int ff_mediacodec_dec_init(AVCodecContext *avctx,
 
 int ff_mediacodec_dec_send(AVCodecContext *avctx,
                            MediaCodecDecContext *s,
-                           AVPacket *pkt);
+                           AVPacket *pkt,
+                           bool wait);
 
 int ff_mediacodec_dec_receive(AVCodecContext *avctx,
                               MediaCodecDecContext *s,