[FFmpeg-devel] [PATCH] support e-ac-3 in mpeg ps/ts

[Måns Rullgård]

Justin Ruggles <justin.ruggles at gmail.com> writes:

> M?ns Rullg?rd wrote:
>> Justin Ruggles <justin.ruggles at gmail.com> writes:
>> 
>>> Hi,
>>>
>>> Here is a patch which adds basic support for E-AC-3 decoding/encoding in
>>> MPEG PS and TS.  The only case I can't seem to differentiate is EVOB,
>>> which uses the same descriptor type and start codes for AC-3 and E-AC-3.
>>>  Since regular AC-3 is also valid E-AC-3, I'm setting them to E-AC-3.
>>>
>>> Index: libavformat/mpegts.c
>>> ===================================================================
>>> --- libavformat/mpegts.c	(revision 15138)
>>> +++ libavformat/mpegts.c	(working copy)
>>> @@ -554,9 +554,12 @@
>>>              if (desc_tag < 0)
>>>                  break;
>>>              if (stream_type == STREAM_TYPE_PRIVATE_DATA) {
>>> -                if((desc_tag == 0x6A) || (desc_tag == 0x7A)) {
>>> +                if (desc_tag == 0x6A) {
>>>                      /*assume DVB AC-3 Audio*/
>>>                      stream_type = STREAM_TYPE_AUDIO_AC3;
>>> +                } else if (desc_tag == 0x7A) {
>>> +                    /* DVB E-AC-3 audio */
>>> +                    stream_type = STREAM_TYPE_AUDIO_EAC3;
>>>                  } else if(desc_tag == 0x7B) {
>>>                      /* DVB DTS audio */
>>>                      stream_type = STREAM_TYPE_AUDIO_DTS;
>>> @@ -627,6 +630,7 @@
>>>          case STREAM_TYPE_AUDIO_AAC:
>>>          case STREAM_TYPE_AUDIO_AC3:
>>>          case STREAM_TYPE_AUDIO_DTS:
>>> +        case STREAM_TYPE_AUDIO_EAC3:
>>>          case STREAM_TYPE_AUDIO_HDMV_DTS:
>>>          case STREAM_TYPE_SUBTITLE_DVB:
>>>              if((stream_type == STREAM_TYPE_AUDIO_HDMV_DTS && !has_hdmv_descr)
>>> @@ -971,6 +975,10 @@
>>>          codec_type = CODEC_TYPE_AUDIO;
>>>          codec_id = CODEC_ID_AC3;
>>>          break;
>>> +    case STREAM_TYPE_AUDIO_EAC3:
>>> +        codec_type = CODEC_TYPE_AUDIO;
>>> +        codec_id = CODEC_ID_EAC3;
>>> +        break;
>>>      case STREAM_TYPE_AUDIO_DTS:
>>>      case STREAM_TYPE_AUDIO_HDMV_DTS:
>>>          codec_type = CODEC_TYPE_AUDIO;
>>> Index: libavformat/mpegts.h
>>> ===================================================================
>>> --- libavformat/mpegts.h	(revision 15138)
>>> +++ libavformat/mpegts.h	(working copy)
>>> @@ -55,6 +55,7 @@
>>>  #define STREAM_TYPE_VIDEO_DIRAC     0xd1
>>>  
>>>  #define STREAM_TYPE_AUDIO_AC3       0x81
>>> +#define STREAM_TYPE_AUDIO_EAC3      0x84
>>>  #define STREAM_TYPE_AUDIO_DTS       0x8a
>>>  #define STREAM_TYPE_AUDIO_HDMV_DTS  0x82
>>> Index: libavformat/mpegtsenc.c
>>> ===================================================================
>>> --- libavformat/mpegtsenc.c	(revision 15138)
>>> +++ libavformat/mpegtsenc.c	(working copy)
>>> @@ -233,6 +233,9 @@
>>>          case CODEC_ID_AC3:
>>>              stream_type = STREAM_TYPE_AUDIO_AC3;
>>>              break;
>>> +        case CODEC_ID_EAC3:
>>> +            stream_type = STREAM_TYPE_AUDIO_EAC3;
>>> +            break;
>>>          default:
>>>              stream_type = STREAM_TYPE_PRIVATE_DATA;
>>>              break;
>> 
>> Where does the value 0x84 come from?  ATSC uses the same stream_type
>> value (0x81) for AC-3 and E-AC-3, differentiating the two using a
>> special descriptor.  DVB sets the stream_type to 6 (private data), and
>> uses different descriptors to distinguish the two types.
>
> That's my mistake... It's supposed to be 0x87 according to ATSC A/53,
> not 0x84.

Now I'm confused.  A/53 does indeed specify 0x87 for stream_type.
However, A/52B can be interpreted as allowing E-AC-3 with stream_type
0x81, if the AC-3_audio_stream_descriptor has a bsid value of 16.
Which is correct?

-- 
M?ns Rullg?rd
mans at mansr.com