avcodec/mediacodecdec: refactor to take advantage of new decoding api

This refactor splits up the main mediacodec decode loop into two
send/receive helpers, which are then used to rewrite the receive_frame
callback and take full advantage of the new decoding api. Since we
can now request packets on demand with ff_decode_get_packet(), the
fifo buffer is no longer necessary and has been removed.

This change was motivated by behavior observed on certain Android TV
devices, featuring hardware mpeg2/h264 decoders which also deinterlace
content (to produce multiple frames per field). Previously, this code
caused buffering issues because queueInputBuffer() was always invoked
before each dequeueOutputBuffer(), even though twice as many output
buffers were being generated.

With this patch, the decoder will always attempt to drain new frames
first before sending more data into the underlying codec.

Signed-off-by: Matthieu Bouron <matthieu.bouron@gmail.com>

1 files changed, 38 insertions, 69 deletions

diff --git a/libavcodec/mediacodecdec.c b/libavcodec/mediacodecdec.c
index cb1151a195..363e12427e 100644
--- a/libavcodec/mediacodecdec.c
+++ b/libavcodec/mediacodecdec.c
@@ -25,7 +25,6 @@
 
 #include "libavutil/avassert.h"
 #include "libavutil/common.h"
-#include "libavutil/fifo.h"
 #include "libavutil/opt.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/pixfmt.h"
@@ -43,8 +42,6 @@ typedef struct MediaCodecH264DecContext {
 
     MediaCodecDecContext *ctx;
 
-    AVFifoBuffer *fifo;
-
     AVPacket buffered_pkt;
 
 } MediaCodecH264DecContext;
@@ -56,8 +53,6 @@ static av_cold int mediacodec_decode_close(AVCodecContext *avctx)
     ff_mediacodec_dec_close(avctx, s->ctx);
     s->ctx = NULL;
 
-    av_fifo_free(s->fifo);
-
     av_packet_unref(&s->buffered_pkt);
 
     return 0;
@@ -400,12 +395,6 @@ static av_cold int mediacodec_decode_init(AVCodecContext *avctx)
 
     av_log(avctx, AV_LOG_INFO, "MediaCodec started successfully, ret = %d\n", ret);
 
-    s->fifo = av_fifo_alloc(sizeof(AVPacket));
-    if (!s->fifo) {
-        ret = AVERROR(ENOMEM);
-        goto done;
-    }
-
 done:
     if (format) {
         ff_AMediaFormat_delete(format);
@@ -418,13 +407,33 @@ 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;
-    int got_frame = 0;
-    int is_eof = 0;
-    AVPacket pkt = { 0 };
 
     /*
      * MediaCodec.flush() discards both input and output buffers, thus we
@@ -452,74 +461,34 @@ static int mediacodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
         }
     }
 
-    ret = ff_decode_get_packet(avctx, &pkt);
-    if (ret == AVERROR_EOF)
-        is_eof = 1;
-    else if (ret == AVERROR(EAGAIN))
-        ; /* no input packet, but fallthrough to check for pending frames */
-    else if (ret < 0)
+    /* flush buffered packet and check for new frame */
+    ret = mediacodec_send_receive(avctx, s, frame, false);
+    if (ret != AVERROR(EAGAIN))
         return ret;
 
-    /* buffer the input packet */
-    if (pkt.size) {
-        if (av_fifo_space(s->fifo) < sizeof(pkt)) {
-            ret = av_fifo_realloc2(s->fifo,
-                                   av_fifo_size(s->fifo) + sizeof(pkt));
-            if (ret < 0) {
-                av_packet_unref(&pkt);
-                return ret;
-            }
-        }
-        av_fifo_generic_write(s->fifo, &pkt, sizeof(pkt), NULL);
-    }
-
-    /* process buffered data */
-    while (!got_frame) {
-        /* prepare the input data */
-        if (s->buffered_pkt.size <= 0) {
-            av_packet_unref(&s->buffered_pkt);
-
-            /* no more data */
-            if (av_fifo_size(s->fifo) < sizeof(AVPacket)) {
-                AVPacket null_pkt = { 0 };
-                if (is_eof) {
-                    ret = ff_mediacodec_dec_decode(avctx, s->ctx, frame,
-                                                   &got_frame, &null_pkt);
-                    if (ret < 0)
-                        return ret;
-                    else if (got_frame)
-                        return 0;
-                    else
-                        return AVERROR_EOF;
-                }
-                return AVERROR(EAGAIN);
-            }
-
-            av_fifo_generic_read(s->fifo, &s->buffered_pkt, sizeof(s->buffered_pkt), NULL);
-        }
+    /* skip fetching new packet if we still have one buffered */
+    if (s->buffered_pkt.size > 0)
+        return AVERROR(EAGAIN);
 
-        ret = ff_mediacodec_dec_decode(avctx, s->ctx, frame, &got_frame, &s->buffered_pkt);
+    /* 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)
             return ret;
-
-        s->buffered_pkt.size -= ret;
-        s->buffered_pkt.data += ret;
     }
+    else if (ret < 0)
+        return ret;
 
-    return 0;
+    /* crank decoder with new packet */
+    return mediacodec_send_receive(avctx, s, frame, true);
 }
 
 static void mediacodec_decode_flush(AVCodecContext *avctx)
 {
     MediaCodecH264DecContext *s = avctx->priv_data;
 
-    while (av_fifo_size(s->fifo)) {
-        AVPacket pkt;
-        av_fifo_generic_read(s->fifo, &pkt, sizeof(pkt), NULL);
-        av_packet_unref(&pkt);
-    }
-    av_fifo_reset(s->fifo);
-
     av_packet_unref(&s->buffered_pkt);
 
     ff_mediacodec_dec_flush(avctx, s->ctx);