[FFmpeg-devel] [PATCH] examples/muxing: improve error messages.

[Stefano Sabatini]

On date Wednesday 2013-01-02 16:03:13 +0100, Nicolas George encoded:
> Illustrate the use of return values, av_err2str and
> avcodec_get_name.
> 
> Signed-off-by: Nicolas George <nicolas.george at normalesup.org>
> ---
>  doc/examples/muxing.c |   45 ++++++++++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/doc/examples/muxing.c b/doc/examples/muxing.c
> index f8b2f7c..8469b27 100644
> --- a/doc/examples/muxing.c
> +++ b/doc/examples/muxing.c
> @@ -63,7 +63,8 @@ static AVStream *add_stream(AVFormatContext *oc, AVCodec **codec,
>      /* find the encoder */
>      *codec = avcodec_find_encoder(codec_id);
>      if (!(*codec)) {
> -        fprintf(stderr, "Could not find codec\n");
> +        fprintf(stderr, "Could not find encoder for '%s'\n",
> +                avcodec_get_name(codec_id));
>          exit(1);
>      }
>  
> @@ -133,12 +134,14 @@ static int audio_input_frame_size;
>  static void open_audio(AVFormatContext *oc, AVCodec *codec, AVStream *st)
>  {
>      AVCodecContext *c;
> +    int ret;
>  
>      c = st->codec;
>  
>      /* open it */
> -    if (avcodec_open2(c, codec, NULL) < 0) {
> -        fprintf(stderr, "Could not open audio codec\n");
> +    ret = avcodec_open2(c, codec, NULL);
> +    if (ret < 0) {
> +        fprintf(stderr, "Could not open audio codec: %s\n", av_err2str(ret));
>          exit(1);
>      }
>  
> @@ -198,7 +201,7 @@ static void write_audio_frame(AVFormatContext *oc, AVStream *st)
>  
>      ret = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
>      if (ret < 0) {
> -        fprintf(stderr, "Error encoding audio frame\n");
> +        fprintf(stderr, "Error encoding audio frame: %s\n", av_err2str(ret));
>          exit(1);
>      }
>  
> @@ -208,8 +211,10 @@ static void write_audio_frame(AVFormatContext *oc, AVStream *st)
>      pkt.stream_index = st->index;
>  
>      /* Write the compressed frame to the media file. */
> -    if (av_interleaved_write_frame(oc, &pkt) != 0) {
> -        fprintf(stderr, "Error while writing audio frame\n");
> +    ret = av_interleaved_write_frame(oc, &pkt);
> +    if (ret != 0) {
> +        fprintf(stderr, "Error while writing audio frame: %s\n",
> +                av_err2str(ret));
>          exit(1);
>      }
>      avcodec_free_frame(&frame);
> @@ -235,8 +240,9 @@ static void open_video(AVFormatContext *oc, AVCodec *codec, AVStream *st)
>      AVCodecContext *c = st->codec;
>  
>      /* open the codec */
> -    if (avcodec_open2(c, codec, NULL) < 0) {
> -        fprintf(stderr, "Could not open video codec\n");
> +    ret = avcodec_open2(c, codec, NULL);
> +    if (ret < 0) {
> +        fprintf(stderr, "Could not open video codec: %s\n", av_err2str(ret));
>          exit(1);
>      }
>  
> @@ -250,7 +256,7 @@ static void open_video(AVFormatContext *oc, AVCodec *codec, AVStream *st)
>      /* Allocate the encoded raw picture. */
>      ret = avpicture_alloc(&dst_picture, c->pix_fmt, c->width, c->height);
>      if (ret < 0) {
> -        fprintf(stderr, "Could not allocate picture\n");
> +        fprintf(stderr, "Could not allocate picture: %s\n", av_err2str(ret));
>          exit(1);
>      }
>  
> @@ -260,7 +266,8 @@ static void open_video(AVFormatContext *oc, AVCodec *codec, AVStream *st)
>      if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
>          ret = avpicture_alloc(&src_picture, AV_PIX_FMT_YUV420P, c->width, c->height);
>          if (ret < 0) {
> -            fprintf(stderr, "Could not allocate temporary picture\n");
> +            fprintf(stderr, "Could not allocate temporary picture: %s\n",
> +                    av_err2str(ret));
>              exit(1);
>          }
>      }
> @@ -346,7 +353,7 @@ static void write_video_frame(AVFormatContext *oc, AVStream *st)
>  
>          ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
>          if (ret < 0) {
> -            fprintf(stderr, "Error encoding video frame\n");
> +            fprintf(stderr, "Error encoding video frame: %s\n", av_err2str(ret));
>              exit(1);
>          }
>  
> @@ -364,7 +371,7 @@ static void write_video_frame(AVFormatContext *oc, AVStream *st)
>          }
>      }
>      if (ret != 0) {
> -        fprintf(stderr, "Error while writing video frame\n");
> +        fprintf(stderr, "Error while writing video frame: %s\n", av_err2str(ret));
>          exit(1);
>      }
>      frame_count++;
> @@ -389,7 +396,7 @@ int main(int argc, char **argv)
>      AVStream *audio_st, *video_st;
>      AVCodec *audio_codec, *video_codec;
>      double audio_pts, video_pts;
> -    int i;
> +    int ret, i;
>  
>      /* Initialize libavcodec, and register all codecs and formats. */
>      av_register_all();
> @@ -441,15 +448,19 @@ int main(int argc, char **argv)
>  
>      /* open the output file, if needed */
>      if (!(fmt->flags & AVFMT_NOFILE)) {
> -        if (avio_open(&oc->pb, filename, AVIO_FLAG_WRITE) < 0) {
> -            fprintf(stderr, "Could not open '%s'\n", filename);
> +        ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
> +        if (ret < 0) {
> +            fprintf(stderr, "Could not open '%s': %s\n", filename,
> +                    av_err2str(ret));
>              return 1;
>          }
>      }
>  
>      /* Write the stream header, if any. */
> -    if (avformat_write_header(oc, NULL) < 0) {
> -        fprintf(stderr, "Error occurred when opening output file\n");
> +    ret = avformat_write_header(oc, NULL);
> +    if (ret < 0) {
> +        fprintf(stderr, "Error occurred when opening output file: %s\n",
> +                av_err2str(ret));
>          return 1;
>      }

LGTM.

BTW we should avoid to exit() from functions, return an error code
instead and do proper cleanup in the calling function (at that point
error reporting could be factorized).
-- 
FFmpeg = Fast & Fantastic Merciless Peaceless Eccentric Goblin