avcodec/mpegvideo_enc: Fix unnecessary linear growth of buffer

If one encodes MJPEG with a single slice and uses input with
AV_FRAME_DATA_ICC_PROFILE side data, the current allocation code
in ff_mpv_encode_picture() will always increase the size of the
temporary buffer used for allocating packets by the size needed
for to write the ICC chunk even when the current buffer is actually
large enough. This commit fixes this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpegvideo_enc.c

@@ -1684,9 +1684,8 @@ int ff_mpv_encode_picture(AVCodecContext *avctx, AVPacket *pkt,
     /* output? */
     if (s->new_picture->data[0]) {
         int growing_buffer = context_count == 1 && !pkt->data && !s->data_partitioning;
-        size_t pkt_size = growing_buffer ? FFMAX(s->mb_width*s->mb_height*64+10000, avctx->internal->byte_buffer_size) - AV_INPUT_BUFFER_PADDING_SIZE
-                                              :
-                                              s->mb_width*s->mb_height*(MAX_MB_BYTES+100)+10000;
+        size_t pkt_size = 10000 + s->mb_width * s->mb_height *
+                                  (growing_buffer ? 64 : (MAX_MB_BYTES + 100));
         if (CONFIG_MJPEG_ENCODER && avctx->codec_id == AV_CODEC_ID_MJPEG) {
             ret = ff_mjpeg_add_icc_profile_size(avctx, s->new_picture, &pkt_size);
             if (ret < 0)
@@ -1694,6 +1693,7 @@ int ff_mpv_encode_picture(AVCodecContext *avctx, AVPacket *pkt,
         }
         if ((ret = ff_alloc_packet(avctx, pkt, pkt_size)) < 0)
             return ret;
+        pkt->size = avctx->internal->byte_buffer_size - AV_INPUT_BUFFER_PADDING_SIZE;
         if (s->mb_info) {
             s->mb_info_ptr = av_packet_new_side_data(pkt,
                                  AV_PKT_DATA_H263_MB_INFO,