lavc: add generic-decode-layer private data

Move AVCodecInternal.nb_draining_errors to it, should should not be
visible outside of decode.c.

libavcodec/avcodec.c

@@ -150,7 +150,9 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
     if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
         return AVERROR(EINVAL);
 
-    avci = av_mallocz(sizeof(*avci));
+    avci = av_codec_is_decoder(codec) ?
+        ff_decode_internal_alloc()    :
+        av_mallocz(sizeof(AVCodecInternal));
     if (!avci) {
         ret = AVERROR(ENOMEM);
         goto end;

libavcodec/avcodec_internal.h

@@ -53,4 +53,6 @@ int ff_decode_preinit(struct AVCodecContext *avctx);
 void ff_decode_flush_buffers(struct AVCodecContext *avctx);
 void ff_encode_flush_buffers(struct AVCodecContext *avctx);
 
+struct AVCodecInternal *ff_decode_internal_alloc(void);
+
 #endif // AVCODEC_AVCODEC_INTERNAL_H

libavcodec/decode.c

@@ -50,6 +50,18 @@
 #include "internal.h"
 #include "thread.h"
 
+typedef struct DecodeContext {
+    AVCodecInternal avci;
+
+    /* to prevent infinite loop on errors when draining */
+    int nb_draining_errors;
+} DecodeContext;
+
+static DecodeContext *decode_ctx(AVCodecInternal *avci)
+{
+    return (DecodeContext *)avci;
+}
+
 static int apply_param_change(AVCodecContext *avctx, const AVPacket *avpkt)
 {
     int ret;
@@ -439,7 +451,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
             int nb_errors_max = 20 + (HAVE_THREADS && avctx->active_thread_type & FF_THREAD_FRAME ?
                                 avctx->thread_count : 1);
 
-            if (avci->nb_draining_errors++ >= nb_errors_max) {
+            if (decode_ctx(avci)->nb_draining_errors++ >= nb_errors_max) {
                 av_log(avctx, AV_LOG_ERROR, "Too many errors when draining, this is a bug. "
                        "Stop draining and force EOF.\n");
                 avci->draining_done = 1;
@@ -1753,5 +1765,10 @@ void ff_decode_flush_buffers(AVCodecContext *avctx)
 
     av_bsf_flush(avci->bsf);
 
-    avci->nb_draining_errors = 0;
+    decode_ctx(avci)->nb_draining_errors = 0;
+}
+
+AVCodecInternal *ff_decode_internal_alloc(void)
+{
+    return av_mallocz(sizeof(DecodeContext));
 }

libavcodec/internal.h

@@ -148,9 +148,6 @@ typedef struct AVCodecInternal {
     AVFrame *buffer_frame;
     int draining_done;
 
-    /* to prevent infinite loop on errors when draining */
-    int nb_draining_errors;
-
     /* used when avctx flag AV_CODEC_FLAG_DROPCHANGED is set */
     int changed_frames_dropped;
     int initial_format;

libavcodec/pthread_frame.c

@@ -28,6 +28,7 @@
 #include <stdint.h>
 
 #include "avcodec.h"
+#include "avcodec_internal.h"
 #include "codec_internal.h"
 #include "decode.h"
 #include "hwconfig.h"
@@ -815,7 +816,7 @@ static av_cold int init_thread(PerThreadContext *p, int *threads_to_free,
     p->parent = fctx;
     p->avctx  = copy;
 
-    copy->internal = av_mallocz(sizeof(*copy->internal));
+    copy->internal = ff_decode_internal_alloc();
     if (!copy->internal)
         return AVERROR(ENOMEM);
     copy->internal->thread_ctx = p;