[FFmpeg-devel] [PATCH] examples/demuxing_decoding: Fix invalidd API usage

[Derek Buitenhuis]

We are not technically allowed to reuse the codec context
found inside the AVStream in the format context.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
---
 doc/examples/demuxing_decoding.c | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/doc/examples/demuxing_decoding.c b/doc/examples/demuxing_decoding.c
index 0ef5df7..c69e07b 100644
--- a/doc/examples/demuxing_decoding.c
+++ b/doc/examples/demuxing_decoding.c
@@ -135,12 +135,11 @@ static int decode_packet(int *got_frame, int cached)
     return decoded;
 }
 
-static int open_codec_context(int *stream_idx,
-                              AVFormatContext *fmt_ctx, enum AVMediaType type)
+static int open_codec_context(int *stream_idx, AVFormatContext *fmt_ctx,
+                              enum AVMediaType type, AVCodecContext **dec_ctx)
 {
     int ret;
     AVStream *st;
-    AVCodecContext *dec_ctx = NULL;
     AVCodec *dec = NULL;
     AVDictionary *opts = NULL;
 
@@ -153,19 +152,37 @@ static int open_codec_context(int *stream_idx,
         *stream_idx = ret;
         st = fmt_ctx->streams[*stream_idx];
 
-        /* find decoder for the stream */
-        dec_ctx = st->codec;
-        dec = avcodec_find_decoder(dec_ctx->codec_id);
+        /* find decoder for the stream as a sanity check */
+        dec = avcodec_find_decoder(st->codec->codec_id);
         if (!dec) {
             fprintf(stderr, "Failed to find %s codec\n",
                     av_get_media_type_string(type));
             return AVERROR(EINVAL);
         }
 
+        /*
+         * Allocate our decoding context, since we are not allowed
+         * to reuse the one from the AVStream
+         */
+        *dec_ctx = avcodec_alloc_context3(NULL);
+        if (!*dec_ctx) {
+            fprintf(stderr, "Failed to allocate %s codec context.\n",
+                    av_get_media_type_string(type));
+            return AVERROR(ENOMEM);
+        }
+
+        /* Copy the properties over */
+        ret = avcodec_copy_context(*dec_ctx, st->codec);
+        if (ret < 0) {
+            fprintf(stderr, "Failed to copy %s codec context.\n",
+                    av_get_media_type_string(type));
+            return AVERROR(EINVAL);
+        }
+
         /* Init the decoders, with or without reference counting */
         if (api_mode == API_MODE_NEW_API_REF_COUNT)
             av_dict_set(&opts, "refcounted_frames", "1", 0);
-        if ((ret = avcodec_open2(dec_ctx, dec, &opts)) < 0) {
+        if ((ret = avcodec_open2(*dec_ctx, dec, &opts)) < 0) {
             fprintf(stderr, "Failed to open %s codec\n",
                     av_get_media_type_string(type));
             return ret;
@@ -252,9 +269,8 @@ int main (int argc, char **argv)
         exit(1);
     }
 
-    if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
+    if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO, &video_dec_ctx) >= 0) {
         video_stream = fmt_ctx->streams[video_stream_idx];
-        video_dec_ctx = video_stream->codec;
 
         video_dst_file = fopen(video_dst_filename, "wb");
         if (!video_dst_file) {
@@ -274,9 +290,8 @@ int main (int argc, char **argv)
         video_dst_bufsize = ret;
     }
 
-    if (open_codec_context(&audio_stream_idx, fmt_ctx, AVMEDIA_TYPE_AUDIO) >= 0) {
+    if (open_codec_context(&audio_stream_idx, fmt_ctx, AVMEDIA_TYPE_AUDIO, &audio_dec_ctx) >= 0) {
         audio_stream = fmt_ctx->streams[audio_stream_idx];
-        audio_dec_ctx = audio_stream->codec;
         audio_dst_file = fopen(audio_dst_filename, "wb");
         if (!audio_dst_file) {
             fprintf(stderr, "Could not open destination file %s\n", video_dst_filename);
-- 
1.9.rc1