[FFmpeg-devel] [PATCH] matroskadec: Export the MuxingApp element value as metadata

[James Almer]

On 01/12/13 2:28 PM, wm4 wrote:
> On Sun, 24 Nov 2013 05:31:48 -0300
> James Almer <jamrial at gmail.com> wrote:
> 
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>  libavformat/matroskadec.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
>> index eb3b4e6..b3a6477 100644
>> --- a/libavformat/matroskadec.c
>> +++ b/libavformat/matroskadec.c
>> @@ -253,6 +253,7 @@ typedef struct {
>>      uint64_t time_scale;
>>      double   duration;
>>      char    *title;
>> +    char    *muxingapp;
>>      EbmlBin date_utc;
>>      EbmlList tracks;
>>      EbmlList attachments;
>> @@ -317,7 +318,7 @@ static EbmlSyntax matroska_info[] = {
>>      { MATROSKA_ID_DURATION,           EBML_FLOAT, 0, offsetof(MatroskaDemuxContext,duration) },
>>      { MATROSKA_ID_TITLE,              EBML_UTF8,  0, offsetof(MatroskaDemuxContext,title) },
>>      { MATROSKA_ID_WRITINGAPP,         EBML_NONE },
>> -    { MATROSKA_ID_MUXINGAPP,          EBML_NONE },
>> +    { MATROSKA_ID_MUXINGAPP,          EBML_UTF8, 0, offsetof(MatroskaDemuxContext,muxingapp) },
>>      { MATROSKA_ID_DATEUTC,            EBML_BIN,  0, offsetof(MatroskaDemuxContext,date_utc) },
>>      { MATROSKA_ID_SEGMENTUID,         EBML_NONE },
>>      { 0 }
>> @@ -1587,6 +1588,7 @@ static int matroska_read_header(AVFormatContext *s)
>>          matroska->ctx->duration = matroska->duration * matroska->time_scale
>>                                    * 1000 / AV_TIME_BASE;
>>      av_dict_set(&s->metadata, "title", matroska->title, 0);
>> +    av_dict_set(&s->metadata, "encoder", matroska->muxingapp, 0);
>>  
>>      if (matroska->date_utc.size == 8)
>>          matroska_metadata_creation_time(&s->metadata, AV_RB64(matroska->date_utc.data));
> 
> Another issue: how is the user supposed to distinguish between real
> metadata (i.e. tags), and random-stuff-dumped-into-the-metadata-dict-
> because-there's-no-other-place entries?

The user can't and never could, as far as i know.
Matroska Tags are read last, for that matter. Currently, if there's a "title" 
or "creation_time" Tag, the relevant existing dict entries (Which were read 
from Matroska Elements as seen in the code above) are overwritten.
This should probably be prevented, to be honest.

And i wouldn't call the values of MATROSKA_ID_TITLE, MATROSKA_ID_MUXINGAPP 
and MATROSKA_ID_DATEUTC random stuff. They are the actual metadata values 
for the relevant dict entries, which is why they are read as such.