[FFmpeg-user] Picture size 0x0 is invalid in FFMPEG log

[Alexander Kulyakhtin]

n my program I'm trying to decode an MPEG4 stream from a certain url and
the decoding fails. Strangely, MPEG4 streams from other urls are decoded
fine, so it's not a problem of the absence of the codec.

Here's how I decode:

1) Find the decoder:

   AVCodec* codec = avcodec_find_decoder(CODEC_ID_MPEG4);

2) Allocate a context

 ACodecContext* ctx = avcodec_alloc_context3(0);

3) Open the codec

avcodec_open2(ctx, codec, 0) // it returns > 0, fine

4) Decoding a packet (which I have)

   avcodec_decode_video2(ctx, frame, &decoded, &packet);

Now avcodec_decode_video2 fails returning -1 and FFMPEG log prints:

*Picture size 0x0 is invalid get_buffer() failed (-1 0 0x0)*

If I manually set up ctx->width and ctx->height before decoding to the
correct values (I know the dimensions of the picture) then it decodes fine.

But I can not be sure of the dimensions all the time, therefore I would
like to know if I can overcome the -1 error.

By seeing the FFMPEG log output can anyone suggest something for me to do?