[FFmpeg-devel] [PATCH] ffprobe: Stash and use width and height before opening the codec

[Derek Buitenhuis]

Some codecs, such as VP6, will only have their correct width and
height set if a few frames have been decoded. This is accomplished
when we call avformat_find_stream_info(). However, we call
avcodec_open2() after this, which can possibly reset the width
and height in the decoder's context to an erroneous value.

Stash and propagate the width and height after calling
avformat_find_stream_info(), but before calling avcodec_open2().

Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
---
 ffprobe.c |   46 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/ffprobe.c b/ffprobe.c
index f70c24c..f4074d4 100644
--- a/ffprobe.c
+++ b/ffprobe.c
@@ -1592,7 +1592,8 @@ static void read_packets(WriterContext *w, AVFormatContext *fmt_ctx)
     }
 }
 
-static void show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_idx)
+static void show_stream(WriterContext *w, AVFormatContext *fmt_ctx,
+                        int stream_idx, int orig_width, int orig_height)
 {
     AVStream *stream = fmt_ctx->streams[stream_idx];
     AVCodecContext *dec_ctx;
@@ -1641,8 +1642,8 @@ static void show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_i
 
         switch (dec_ctx->codec_type) {
         case AVMEDIA_TYPE_VIDEO:
-            print_int("width",        dec_ctx->width);
-            print_int("height",       dec_ctx->height);
+            print_int("width",        orig_width);
+            print_int("height",       orig_height);
             print_int("has_b_frames", dec_ctx->has_b_frames);
             sar = av_guess_sample_aspect_ratio(fmt_ctx, stream, NULL);
             if (sar.den) {
@@ -1742,13 +1743,19 @@ static void show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_i
     fflush(stdout);
 }
 
-static void show_streams(WriterContext *w, AVFormatContext *fmt_ctx)
+typedef struct Dimension {
+    int width;
+    int height;
+} Dimension;
+
+static void show_streams(WriterContext *w, AVFormatContext *fmt_ctx,
+                         Dimension *orig_dims)
 {
     int i;
     writer_print_section_header(w, SECTION_ID_STREAMS);
     for (i = 0; i < fmt_ctx->nb_streams; i++)
         if (selected_streams[i])
-            show_stream(w, fmt_ctx, i);
+            show_stream(w, fmt_ctx, i, orig_dims[i].width, orig_dims[i].height);
     writer_print_section_footer(w);
 }
 
@@ -1791,7 +1798,8 @@ static void show_error(WriterContext *w, int err)
     writer_print_section_footer(w);
 }
 
-static int open_input_file(AVFormatContext **fmt_ctx_ptr, const char *filename)
+static int open_input_file(AVFormatContext **fmt_ctx_ptr, const char *filename,
+                           Dimension **orig_dims)
 {
     int err, i;
     AVFormatContext *fmt_ctx = NULL;
@@ -1807,8 +1815,6 @@ static int open_input_file(AVFormatContext **fmt_ctx_ptr, const char *filename)
         return AVERROR_OPTION_NOT_FOUND;
     }
 
-
-    /* fill the streams in the format context */
     if ((err = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
         print_error(filename, err);
         return err;
@@ -1816,11 +1822,27 @@ static int open_input_file(AVFormatContext **fmt_ctx_ptr, const char *filename)
 
     av_dump_format(fmt_ctx, 0, filename, 0);
 
+    /*
+     * Allocate our dimensions buffer.
+     * We need to stash the dimensions before we call avcodec_open2(),
+     * because some codecs require a few frames to be decoded before
+     * width and height are set properly, and avcodec_open2() can
+     * reset these values.
+     */
+    if (!(*orig_dims = av_mallocz(sizeof(**orig_dims) * fmt_ctx->nb_streams))) {
+        av_log(NULL, AV_LOG_ERROR,
+               "Could not allocate temporary dimensions buffer.\n");
+        return AVERROR(ENOMEM);
+    }
+
     /* bind a decoder to each input stream */
     for (i = 0; i < fmt_ctx->nb_streams; i++) {
         AVStream *stream = fmt_ctx->streams[i];
         AVCodec *codec;
 
+        (*orig_dims)[i].width  = stream->codec->width;
+        (*orig_dims)[i].height = stream->codec->height;
+
         if (stream->codec->codec_id == AV_CODEC_ID_PROBE) {
             av_log(NULL, AV_LOG_ERROR,
                    "Failed to probe codec for input stream %d\n",
@@ -1855,13 +1877,14 @@ static void close_input_file(AVFormatContext **ctx_ptr)
 static int probe_file(WriterContext *wctx, const char *filename)
 {
     AVFormatContext *fmt_ctx;
+    Dimension *orig_dims;
     int ret, i;
     int section_id;
 
     do_read_frames = do_show_frames || do_count_frames;
     do_read_packets = do_show_packets || do_count_packets;
 
-    ret = open_input_file(&fmt_ctx, filename);
+    ret = open_input_file(&fmt_ctx, filename, &orig_dims);
     if (ret >= 0) {
         nb_streams_frames  = av_calloc(fmt_ctx->nb_streams, sizeof(*nb_streams_frames));
         nb_streams_packets = av_calloc(fmt_ctx->nb_streams, sizeof(*nb_streams_packets));
@@ -1896,7 +1919,7 @@ static int probe_file(WriterContext *wctx, const char *filename)
                 writer_print_section_footer(wctx);
         }
         if (do_show_streams)
-            show_streams(wctx, fmt_ctx);
+            show_streams(wctx, fmt_ctx, orig_dims);
         if (do_show_format)
             show_format(wctx, fmt_ctx);
 
@@ -1906,6 +1929,9 @@ static int probe_file(WriterContext *wctx, const char *filename)
         av_freep(&nb_streams_packets);
         av_freep(&selected_streams);
     }
+
+    av_freep(&orig_dims);
+
     return ret;
 }
 
-- 
1.7.10.4