IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
WMA: Stream Properties Object (WAVEFORMATEX)
Liandril
post Aug 27 2010, 19:40
Post #1





Group: Members
Posts: 5
Joined: 27-August 10
Member No.: 83419



Hi everyone and first of all: sorry for my English!

I'm currently writing an extraction tool for a german game that uses .xwb-files (Microsoft XACT Wavebanks). There
are already quite a lot of xwb extraction tools, but most of them only work for older games, because Microsoft
changes the file format from time to time. So "old" extraction tools won't work with "new" xwbs.

xwb files can contain a collection of waves (pcm, adpcm, wma or xma). Unfortunately, there is currently no tool
that's able to extract wma data from "newer" xwb files... therefor I'm writing my tool, trying to extract the .xwb to valid .wma files.
Extracting the wma DATA is quite easy and I'm able to transform them to a ASF DATA OBJECT (probably you know: wma is actually ASF
(roughly spoken). And a valid .wma file consists of at least 5 objects:Header Object, File Properties Object, Stream Properties
Object, Header Extension Object and Data Object).
My problem is the Stream Properties Object which contains a WAVEFORMATEX structure. Appended to the WAVEFORMATEX
structure is a "Code Specific Data Section" for WMA (which is not described in the ASF Specification):

dwSamplesPerBlock DWORD
wEncodeOptions WORD
dwSuperBlockAlign DWORD

Unfortunately I've no idea how to determine the values for these fields (especially the wEncodeOptions). crying.gif
So I'd really, really appreciate, if someone could give me a hint about this WMA-Code specific data section...
Thanks a lot!

This post has been edited by Liandril: Aug 27 2010, 19:42
Go to the top of the page
+Quote Post
saratoga
post Aug 27 2010, 20:28
Post #2





Group: Members
Posts: 4996
Joined: 2-September 02
Member No.: 3264



Most of the fields in the Stream Properties Object will come from whatever container you're taking the stream from. From the rockbox ASF parser:

CODE
                        read_uint16le(fd, &wfx->codec_id);
                        read_uint16le(fd, &wfx->channels);
                        read_uint32le(fd, &wfx->rate);
                        read_uint32le(fd, &wfx->bitrate);
                        wfx->bitrate *= 8;
                        read_uint16le(fd, &wfx->blockalign);
                        read_uint16le(fd, &wfx->bitspersample);
                        read_uint16le(fd, &wfx->datalen);

....

                       } else if (wfx->codec_id == ASF_CODEC_ID_WMAV2) {
                            read(fd, wfx->data, 6);
                            lseek(fd,current.size - 24 - 72 - 6,SEEK_CUR);
                            wfx->audiostream = flags&0x7f;
                        }

...

     extradata = wfx->data;
    if (s->version == 1 && wfx->datalen >= 4) {
        flags2 = extradata[2] | (extradata[3] << 8);
    }else if (s->version == 2 && wfx->datalen >= 6){
        flags2 = extradata[4] | (extradata[5] << 8);
    }
    s->use_exp_vlc = flags2 & 0x0001;
    s->use_bit_reservoir = flags2 & 0x0002;
    s->use_variable_block_len = flags2 & 0x0004;


So basically the fields in that struct are things like sample rate, transform size and any misc features the codec needs enabled (like variable length coding for exponents). The asf view tool gives you some hints (sample rate, etc) but won't tell you about block lengths and such (I think it lumps those into the "extra data" field of the stream properties object).
Go to the top of the page
+Quote Post
Liandril
post Aug 27 2010, 21:46
Post #3





Group: Members
Posts: 5
Joined: 27-August 10
Member No.: 83419



QUOTE (saratoga @ Aug 27 2010, 21:28) *
Most of the fields in the Stream Properties Object will come from whatever container you're taking the stream from. From the rockbox ASF parser:

CODE
            
....
                       } else if (wfx->codec_id == ASF_CODEC_ID_WMAV2) {
                            read(fd, wfx->data, 6);
                            lseek(fd,current.size - 24 - 72 - 6,SEEK_CUR);
                            wfx->audiostream = flags&0x7f;
                        }
...
     extradata = wfx->data;
    if (s->version == 1 && wfx->datalen >= 4) {
        flags2 = extradata[2] | (extradata[3] << 8);
    }else if (s->version == 2 && wfx->datalen >= 6){
        flags2 = extradata[4] | (extradata[5] << 8);
    }
    s->use_exp_vlc = flags2 & 0x0001;
    s->use_bit_reservoir = flags2 & 0x0002;
    s->use_variable_block_len = flags2 & 0x0004;


So basically the fields in that struct are things like sample rate, transform size and any misc features the codec needs enabled (like variable length coding for exponents). The asf view tool gives you some hints (sample rate, etc) but won't tell you about block lengths and such (I think it lumps those into the "extra data" field of the stream properties object).

Wow, thanks a lot for the quick response smile.gif ... I posted my request in other audio forums/file format forums quite a while ago... and didn't receive ANY answer so far.. so: THANKS! From the infos within the .xwb file, I can get/calculate the values "within" the WAVEFORMATEX structure (channels, bitrate, block align/length, bitspersample)... my problem are just the extradata / codec specific data... so thanks for this code. I'll try to figure out, what it means
Go to the top of the page
+Quote Post
saratoga
post Aug 27 2010, 22:04
Post #4





Group: Members
Posts: 4996
Joined: 2-September 02
Member No.: 3264



If it helps virtually all WMA files in existence define use_exp_vlc = use_bit_reservoir = use_variable_block_len = 1. Knowing that, the sample rate, bits per sample, etc you might be able to track down the resulting bytes in the source bitstream.
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 30th September 2014 - 17:56