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>

1 files changed, 42 insertions, 38 deletions

diff --git a/libavcodec/mediacodecdec.c b/libavcodec/mediacodecdec.c
index 86ceee5a83..2ac22dd1f6 100644
--- a/libavcodec/mediacodecdec.c
+++ b/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)