[Libav-user] Can't get MPEG4 decoder

[Michael IV]

But now I see in vlc that the MPEG4 codec is actually named "mp4v" .So
that's the name I have to specificy in --enable-decoder when doing FFMPEG
config?


On Thu, Nov 9, 2017 at 7:26 PM, Michael IV <explomaster at gmail.com> wrote:

> And testing the actual codecId of the video stream in the file I am also
> getting NULL for avcodec_find_decoder:
>
>         ret = av_find_best_stream(pFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1,
> NULL, 0);
> st = pFormatCtx->streams[ret];
> AVCodecContext *dec_ctx = NULL;
> AVCodec *dec = NULL;
> dec_ctx = st->codec;
> dec = avcodec_find_decoder(dec_ctx->codec_id);
>
>   * where ec_ctx->codec_id == AV_CODEC_ID_MPEG4*
>
> On Thu, Nov 9, 2017 at 7:22 PM, Michael IV <explomaster at gmail.com> wrote:
>
>> Hi, thanks for the input. Now I am confused even more. All  I need is to
>> start demuxing an mp4 file. Those codecs test above is not what I do.
>> I started to check those because I am getting into trouble in this part:
>>
>>         pFormatCtx = avformat_alloc_context();  //ok
>> AVDictionary *d = NULL;
>> av_dict_set(&d, "protocol_whitelist","file", 0);  //ok
>>         int ret = avformat_open_input(&pFormatCtx, in_f_name , NULL,
>> &d);  //ok
>>          avformat_find_stream_info(pFormatCtx, NULL) ///also ok
>>
>> But once I get to access the codecpar I hit  "access violation reading
>> location:
>>
>> *pFormatCtx->streams[i]->codecpar->codec_type==AVMEDIA_TYPE_VIDEO*
>>
>> Because my *codecpar *is not initialized. That's what I don't understand
>> here.
>>
>>
>>
>>
>>
>> On Nov 9, 2017 8:14 PM, "Carl Eugen Hoyos" <ceffmpeg at gmail.com> wrote:
>>
>>> Hi!
>>>
>>> > Am 09.11.2017 um 17:13 schrieb Michael IV <explomaster at gmail.com>:
>>> >
>>> > Hi All. What maybe a reason that  avcodec_find_decoder returns NULL ?
>>> >
>>> > I enabled in my FFMPEG build MOV and h264 demuxer. Configure report
>>> clearly
>>> > states that.
>>> >
>>> > But doing this test:
>>> >
>>> >          av_register_all();
>>> >        avcodec_register_all();
>>> >          avformat_network_init();
>>> >          AVCodec* h264codc = avcodec_find_decoder_by_name("h264");
>>>
>>> This is supposed to work.
>>>
>>>
>>> >        AVCodec* h264codc1 = avcodec_find_decoder_by_name("MOV");
>>>
>>> This is not the name of any decoder, mov is a file format, you will find
>>> a demuxer (and a muxer) with that name (I think).
>>>
>>> >        AVCodec* h264codc3 = avcodec_find_decoder_by_name("MPEG4");
>>>
>>> There is codec "mpeg4" but that's not h264.
>>>
>>> >        AVCodec* h264codc4 = avcodec_find_decoder_by_name("MP4");
>>>
>>> See above for mov, although the same demuxer handles mov and mp4.
>>>
>>> >        AVCodec* h264codc5 = avcodec_find_decoder(AV_CODEC_ID_MPEG4);
>>>
>>> Again, this codec exists but it's not h264.
>>>
>>> > Only h264codc  returns a valid codec.
>>>
>>>
>>> > The only thing I didn't do during build config was not to enable
>>> libx264.
>>>
>>> This only means that you have no h264 encoder.
>>>
>>> > May this be the source of the problem? I didn't do that because I just
>>> need to demux  mp4 movie and get its elementary stream.
>>>
>>> Then you don't care about a decoder, you only need a demuxer (and maybe
>>> a parser).
>>>
>>> Carl Eugen
>>> _______________________________________________
>>> Libav-user mailing list
>>> Libav-user at ffmpeg.org
>>> http://ffmpeg.org/mailman/listinfo/libav-user
>>>
>>
>
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