[Vorbis-dev] [libtremor] ov_read is reading past file size

[Stephen Damm]

On 12-06-09 06:26 PM, Stephen Damm wrote:
> I have a wav file which has been converted to an ogg file with 
> libvorbis via ffmpeg.  However I've tested a few files just to make sure.
>
> I run a standard while loop to using ov_read to pull all the data out 
> of ogg file.  Using 4096 as the size to read each call.  Watching my 
> debug logs it is reading 2048 bytes each call.
>
> When I load the wav file the data chunk for the pcm data is 167680 
> bytes.  Running the file in audacity proves this size to be accurate.
>
> When I load the ogg file, ov_read goes past that size ending on 168320 
> bytes, which causes some memory corruption further down in the program.
>
> If I force the while loop running ov_read to stop one read before, 
> 166272 bytes, then everything is fine except the sound clip cuts off a 
> few samples early.  If I let it do the final ov_read call it attempts 
> to read up to 168320 bytes, which is past what the PCM data actually 
> is and the allocated buffer size.
>
> unsigned int uiPCMSamples = (unsigned int)ov_pcm_total(&vf, -1);
> unsigned int totalPCMSize = uiPCMSamples * vi->channels * sizeof(short);
> void* pvPCMBuffer = malloc(totalPCMSize);
>
> This yields 167680 bytes, so tremor knows how much PCM data there is.  
> However ov_read is just going ahead and skipping past that number 
> reading up to 168320 bytes.
>
> So either I have to increase the size of my pvPCMBuffer by some magic 
> number or tremor is reading to far.
>
>
>         int current_section = 0;
>         long iRead = 0;
>         unsigned int uiCurrPos = 0;
>         do
>         {
>             iRead = ov_read(&vf, (char*)pvPCMBuffer + uiCurrPos, 4096, 
> &current_section);
>             uiCurrPos += (unsigned int)iRead;
>         }
>         while (iRead != 0);
>
>
> I've tried everything assuming I'm the cause of the problem.  Although 
> now I am leaning on tremor having an issue.
>
>
> (I posted to tremor mailing list first but it is labelled as 
> deprecated and pointed to this one as the mailing list for it)
>
>
> Thanks,
> Stephen Damm

Solution was simply to add:

ov_pcm_seek(&vf, 0);

Not entirely sure why.  No other examples do this.  However all the size 
reads line up now.