lavc/encode: add an encoder-specific get_buffer() variant

Several encoders (roqvideo, svq1, snow, and the mpegvideo family)
currently call ff_get_buffer(). However this function is written
assuming it is called by a decoder. Though nothing has been obviously
broken by this until now, that may change in the future.

To avoid potential future issues, introduce a simple encode-specific
wrapper around avcodec_default_get_buffer2() and enforce its use in
encoders.

libavcodec/decode.c

@@ -1405,6 +1405,8 @@ int ff_get_buffer(AVCodecContext *avctx, AVFrame *frame, int flags)
     int override_dimensions = 1;
     int ret;
 
+    av_assert0(av_codec_is_decoder(avctx->codec));
+
     if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
         if ((unsigned)avctx->width > INT_MAX - STRIDE_ALIGN ||
             (ret = av_image_check_size2(FFALIGN(avctx->width, STRIDE_ALIGN), avctx->height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx)) < 0 || avctx->pix_fmt<0) {

libavcodec/encode.c

@@ -597,3 +597,37 @@ int ff_encode_preinit(AVCodecContext *avctx)
 
     return 0;
 }
+
+int ff_encode_alloc_frame(AVCodecContext *avctx, AVFrame *frame)
+{
+    int ret;
+
+    switch (avctx->codec->type) {
+    case AVMEDIA_TYPE_VIDEO:
+        frame->format = avctx->pix_fmt;
+        if (frame->width <= 0 || frame->height <= 0) {
+            frame->width  = FFMAX(avctx->width,  avctx->coded_width);
+            frame->height = FFMAX(avctx->height, avctx->coded_height);
+        }
+
+        break;
+    case AVMEDIA_TYPE_AUDIO:
+        frame->sample_rate = avctx->sample_rate;
+        frame->format      = avctx->sample_fmt;
+        if (!frame->ch_layout.nb_channels) {
+            ret = av_channel_layout_copy(&frame->ch_layout, &avctx->ch_layout);
+            if (ret < 0)
+                return ret;
+        }
+        break;
+    }
+
+    ret = avcodec_default_get_buffer2(avctx, frame, 0);
+    if (ret < 0) {
+        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
+        av_frame_unref(frame);
+        return ret;
+    }
+
+    return 0;
+}

libavcodec/encode.h

@@ -44,6 +44,11 @@ int ff_encode_get_frame(AVCodecContext *avctx, AVFrame *frame);
  */
 int ff_get_encode_buffer(AVCodecContext *avctx, AVPacket *avpkt, int64_t size, int flags);
 
+/**
+ * Allocate buffers for a frame. Encoder equivalent to ff_get_buffer().
+ */
+int ff_encode_alloc_frame(AVCodecContext *avctx, AVFrame *frame);
+
 /**
  * Check AVPacket size and allocate data.
  *

libavcodec/mpegpicture.c

@@ -26,6 +26,7 @@
 #include "libavutil/imgutils.h"
 
 #include "avcodec.h"
+#include "encode.h"
 #include "motion_est.h"
 #include "mpegpicture.h"
 #include "mpegutils.h"
@@ -123,14 +124,15 @@ static int alloc_frame_buffer(AVCodecContext *avctx,  Picture *pic,
     int r, ret;
 
     pic->tf.f = pic->f;
-    if (avctx->codec_id != AV_CODEC_ID_WMV3IMAGE &&
-        avctx->codec_id != AV_CODEC_ID_VC1IMAGE  &&
-        avctx->codec_id != AV_CODEC_ID_MSS2) {
-        if (edges_needed) {
-            pic->f->width  = avctx->width  + 2 * EDGE_WIDTH;
-            pic->f->height = avctx->height + 2 * EDGE_WIDTH;
-        }
 
+    if (edges_needed) {
+        pic->f->width  = avctx->width  + 2 * EDGE_WIDTH;
+        pic->f->height = avctx->height + 2 * EDGE_WIDTH;
+
+        r = ff_encode_alloc_frame(avctx, pic->f);
+    } else if (avctx->codec_id != AV_CODEC_ID_WMV3IMAGE &&
+               avctx->codec_id != AV_CODEC_ID_VC1IMAGE  &&
+               avctx->codec_id != AV_CODEC_ID_MSS2) {
         r = ff_thread_get_ext_buffer(avctx, &pic->tf,
                                      pic->reference ? AV_GET_BUFFER_FLAG_REF : 0);
     } else {

libavcodec/roqvideoenc.c

@@ -1081,8 +1081,8 @@ static int roq_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     if (enc->first_frame) {
         /* Alloc memory for the reconstruction data (we must know the stride
          for that) */
-        if ((ret = ff_get_buffer(avctx, roq->current_frame, 0)) < 0 ||
-            (ret = ff_get_buffer(avctx, roq->last_frame,    0)) < 0)
+        if ((ret = ff_encode_alloc_frame(avctx, roq->current_frame)) < 0 ||
+            (ret = ff_encode_alloc_frame(avctx, roq->last_frame   )) < 0)
             return ret;
 
         /* Before the first video frame, write a "video info" chunk */

libavcodec/snow.c

@@ -23,6 +23,7 @@
 #include "libavutil/opt.h"
 #include "libavutil/thread.h"
 #include "avcodec.h"
+#include "encode.h"
 #include "me_cmp.h"
 #include "snow_dwt.h"
 #include "internal.h"
@@ -76,8 +77,11 @@ int ff_snow_get_buffer(SnowContext *s, AVFrame *frame)
     if (edges_needed) {
         frame->width  += 2 * EDGE_WIDTH;
         frame->height += 2 * EDGE_WIDTH;
-    }
-    if ((ret = ff_get_buffer(s->avctx, frame, AV_GET_BUFFER_FLAG_REF)) < 0)
+
+        ret = ff_encode_alloc_frame(s->avctx, frame);
+    } else
+        ret = ff_get_buffer(s->avctx, frame, AV_GET_BUFFER_FLAG_REF);
+    if (ret < 0)
         return ret;
     if (edges_needed) {
         for (i = 0; frame->data[i]; i++) {

libavcodec/svq1enc.c

@@ -595,12 +595,12 @@ static int svq1_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     }
 
     if (!s->current_picture->data[0]) {
-        if ((ret = ff_get_buffer(avctx, s->current_picture, 0)) < 0) {
+        if ((ret = ff_encode_alloc_frame(avctx, s->current_picture)) < 0) {
             return ret;
         }
     }
     if (!s->last_picture->data[0]) {
-        ret = ff_get_buffer(avctx, s->last_picture, 0);
+        ret = ff_encode_alloc_frame(avctx, s->last_picture);
         if (ret < 0)
             return ret;
     }