[FFmpeg-devel] [PATCH 2/2] avcodec/decode: use a packet list to store packet properties

[James Almer]

Keeping only the latest packet fed to the decoder works only for decoders that
return a frame immediately after every consumed packet. Decoders that consume
several packets before they return a frame will fill said frame with properties
taken from the last consumed packet instead of the earliest.

Signed-off-by: James Almer <jamrial at gmail.com>
---
This essentially enables decoders implementing the AVCodec.receive_frame API to
not require having to deal with timestamps and such properties internally, and
letting ff_decode_frame_props() do all the work instead (See libdav1d, which
i'll adapt once this goes in).

As an example, this fixes the timestamps for the audio track in
bink/binkaudio_rdft.bik from the FATE suite, where the decoder wrongly assumed
ff_decode_frame_props() alone would handle them right.
The reason the relevant fate test is unaffected is because it just compares the
decoded output with a reference pcm file.

Haven't looked too much into it, but i assume this change could simplify some
AV_CODEC_CAP_DELAY decoders that keep track of timestamps, even those using the
old AVCodec.decode() API.

 libavcodec/decode.c   | 34 +++++++++++++++++++++++++---------
 libavcodec/internal.h |  2 ++
 libavcodec/utils.c    |  3 +++
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index da587ac1f6..de36e28d3c 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -43,6 +43,7 @@
 #include "decode.h"
 #include "hwconfig.h"
 #include "internal.h"
+#include "packet_internal.h"
 #include "thread.h"
 
 typedef struct FramePool {
@@ -142,15 +143,22 @@ fail2:
     return 0;
 }
 
-static int extract_packet_props(AVCodecInternal *avci, const AVPacket *pkt)
+#define IS_EMPTY(pkt) (!(pkt)->data && !(pkt)->side_data_elems)
+
+static int extract_packet_props(AVCodecInternal *avci, AVPacket *pkt)
 {
     int ret = 0;
 
-    av_packet_unref(avci->last_pkt_props);
-    if (pkt) {
-        ret = av_packet_copy_props(avci->last_pkt_props, pkt);
-        if (!ret)
-            avci->last_pkt_props->size = pkt->size; // HACK: Needed for ff_decode_frame_props().
+    ret = avpriv_packet_list_put(&avci->pkt_props, &avci->pkt_props_tail, pkt,
+                                 FF_PACKETLIST_FLAG_REF_PACKET);
+    if (ret < 0)
+        return ret;
+
+    if (IS_EMPTY(avci->last_pkt_props)) {
+        ret = avpriv_packet_list_get(&avci->pkt_props,
+                                     &avci->pkt_props_tail,
+                                     avci->last_pkt_props);
+        av_assert0(ret != AVERROR(EAGAIN));
     }
     return ret;
 }
@@ -512,6 +520,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
 
     if (ret >= pkt->size || ret < 0) {
         av_packet_unref(pkt);
+        av_packet_unref(avci->last_pkt_props);
     } else {
         int consumed = ret;
 
@@ -550,9 +559,11 @@ static int decode_receive_frame_internal(AVCodecContext *avctx, AVFrame *frame)
 
     av_assert0(!frame->buf[0]);
 
-    if (avctx->codec->receive_frame)
+    if (avctx->codec->receive_frame) {
         ret = avctx->codec->receive_frame(avctx, frame);
-    else
+        if (ret != AVERROR(EAGAIN))
+            av_packet_unref(avci->last_pkt_props);
+    } else
         ret = decode_simple_receive_frame(avctx, frame);
 
     if (ret == AVERROR_EOF)
@@ -1683,7 +1694,7 @@ static int add_metadata_from_side_data(const AVPacket *avpkt, AVFrame *frame)
 
 int ff_decode_frame_props(AVCodecContext *avctx, AVFrame *frame)
 {
-    const AVPacket *pkt = avctx->internal->last_pkt_props;
+    AVPacket *pkt = avctx->internal->last_pkt_props;
     int i;
     static const struct {
         enum AVPacketSideDataType packet;
@@ -1701,6 +1712,11 @@ int ff_decode_frame_props(AVCodecContext *avctx, AVFrame *frame)
         { AV_PKT_DATA_S12M_TIMECODE,              AV_FRAME_DATA_S12M_TIMECODE },
     };
 
+    if (IS_EMPTY(pkt))
+        avpriv_packet_list_get(&avctx->internal->pkt_props,
+                               &avctx->internal->pkt_props_tail,
+                               pkt);
+
     if (pkt) {
         frame->pts = pkt->pts;
 #if FF_API_PKT_PTS
diff --git a/libavcodec/internal.h b/libavcodec/internal.h
index 5d0e6e7831..ce4dbbc2b9 100644
--- a/libavcodec/internal.h
+++ b/libavcodec/internal.h
@@ -145,6 +145,8 @@ typedef struct AVCodecInternal {
      * for decoding.
      */
     AVPacket *last_pkt_props;
+    AVPacketList *pkt_props;
+    AVPacketList *pkt_props_tail;
 
     /**
      * temporary buffer used for encoders to store their bitstream
diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 14cb5cf1aa..4a180a1500 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -50,6 +50,7 @@
 #include "thread.h"
 #include "frame_thread_encoder.h"
 #include "internal.h"
+#include "packet_internal.h"
 #include "put_bits.h"
 #include "raw.h"
 #include "bytestream.h"
@@ -1149,6 +1150,8 @@ av_cold int avcodec_close(AVCodecContext *avctx)
         av_packet_free(&avctx->internal->compat_encode_packet);
         av_packet_free(&avctx->internal->buffer_pkt);
         av_packet_free(&avctx->internal->last_pkt_props);
+        avpriv_packet_list_free(&avctx->internal->pkt_props,
+                                &avctx->internal->pkt_props_tail);
 
         av_packet_free(&avctx->internal->ds.in_pkt);
         av_frame_free(&avctx->internal->es.in_frame);
-- 
2.27.0