Re: audio device on ubuntu

On Sun, Aug 30, 2009 at 3:30 PM, Dan Dennedy<[email protected]> wrote:
> On Sun, Aug 30, 2009 at 9:42 AM, Carl Karsten<[email protected]> wrote:
>> On Sat, Aug 29, 2009 at 11:29 PM, Dan Dennedy<[email protected]> wrote:
>>> On Sat, Aug 29, 2009 at 5:45 PM, Carl Karsten<[email protected]> wrote:
>>>> It seams to be playing at 1x.
>>>
>>> That message is not based on what speed you are playing at; it is
>>> based on what speed it was at when you recorded. It could be that the
>>> message only appears for a couple of frames and you have some other
>>> audio output problem. Do you think you are getting the message for
>>> each frame while playing.
>>
>> yes.  played 30 frames, got 30 lines of # no audio
>
> OK
>
>>>
>>>> It is dv from dvgrab/dvswitch, should be
>>>> fine.
>>
>> Actually, some new dvswitch  code was written back in March that
>> creates a dv stream from alsa (black video.)  There is a chance that
>> it isn't quite right.
>>
>> you mind reviewing some code:
>>
>> dvsource-alsa calls dv_buffer_set_audio in dif_audio.c
>>
>> http://svn.debian.org/wsvn/dvswitch/trunk/src/dvsource-alsa.c
>> http://svn.debian.org/wsvn/dvswitch/trunk/src/dif_audio.c
>>
>> void dv_buffer_set_audio(uint8_t * buffer,
>>                         enum dv_sample_rate sample_rate_code,
>>                         unsigned frame_count, const int16_t * samples)
>> {
>>    const struct dv_system * system = dv_buffer_system(buffer);
>>
>>    assert(sample_rate_code >= 0 && sample_rate_code < dv_sample_rate_count);
>>    assert(frame_count >= system->audio_frame_counts[sample_rate_code].min &&
>>           frame_count <= system->audio_frame_counts[sample_rate_code].max);
>>
>>    bool use_12bit = sample_rate_code == dv_sample_rate_32k;
>>    unsigned sample_count = frame_count * 2; // stereo
>>
>>    // Each audio block has a 3-byte block id, a 5-byte AAUX
>>    // pack, and 72 bytes of samples.  Audio block 3 in each
>>    // sequence has an AS (audio source) pack, audio block 4
>>    // has an ASC (audio source control) pack, and the other
>>    // packs seem to be optional.
>>    static const uint8_t aaux_blank_pack[DIF_PACK_SIZE] = {
>>        0xFF, 0xFF, 0xFF, 0xFF, 0xFF
>>    };
>>    uint8_t aaux_as_pack[DIF_PACK_SIZE] = {
>>        // pack id; 0x50 for AAUX source
>>        0x50,
>>        // bits 0-5: number of audio frames in video frame minus minimum value
>>        // bit 6: flag "should be 1"
>>        // bit 7: flag for unlocked audio sampling
>>        (frame_count - system->audio_frame_counts[sample_rate_code].min)
>>        | (1 << 6) | (1 << 7),
>>        // bits 0-3: audio mode
>>        // bit 4: flag for independent channels
>>        // bit 5: flag for "lumped" stereo (?)
>>        // bits 6-7: number of audio channels per block minus 1
>>        use_12bit << 6,
>>        // bits 0-4: system type; 0x0 for DV
>>        // bit 5: frame rate; 0 for 29.97 fps, 1 for 25 fps
>>        // bit 6: flag for multi-language audio
>>        // bit 7: ?
>>        dv_buffer_system_code(buffer) << 5,
>>        // bits 0-2: quantisation; 0 for 16-bit LPCM, 1 for 12-bit
>>        // bits 3-5: sample rate code
>>        // bit 6: time constant of emphasis; must be 1
>>        // bit 7: flag for no emphasis
>>        use_12bit | (sample_rate_code << 3) | (1 << 6) | (1 << 7)
>>    };
>>    static const uint8_t aaux_asc_pack[DIF_PACK_SIZE] = {
>>        // pack id; 0x51 for AAUX source control
>>        0x51,
>>        // bits 0-1: emphasis flag and ?
>>        // bits 2-3: compression level; 0 for once
>>        // bits 4-5: input type; 1 for digital
>>        // bits 6-7: copy generation management system; 0 for unrestricted
>>        (1 << 4),
>>        // bits 0-2: ?
>>        // bits 3-5: recording mode; 1 for original (XXX should indicate dub)
>>        // bit 6: recording end flag, inverted
>>        // bit 7: recording start flag, inverted
>>        (1 << 3) | (1 << 6) | (1 << 7),
>>        // bits 0-6: speed; 0x20 seems to be normal
>>        // bit 7: direction: 1 for forward
>>        0x20 | (1 << 7),
>
> Here is how libdv interprets this and causes 'no audio' messages:
> int dv_is_normal_speed (dv_decoder_t *dv)
> {
>  int normal_speed = TRUE;
>
>  if (dv->std == e_dv_std_iec_61834) {
>    normal_speed = (dv->audio->aaux_asc.pc3.speed == 0x20);
>  } else if (dv->std == e_dv_std_smpte_314m) {
>    if(dv->audio->aaux_as.pc3.system) {
>      /* PAL */
>      normal_speed = (dv->audio->aaux_asc.pc3.speed == 0x64);
>    } else {
>      /* NTSC */
>      normal_speed = (dv->audio->aaux_asc.pc3.speed == 0x78);
>    } /* else */
>  }
>  return normal_speed;
>
> I bet dvsource-alsa.c is signaling this as a smpte stream and not iec.
> As can be seen below from libdv, that is determined by the APT field
> in some DV header.
>
>    dv->std = ((header->apt) ? e_dv_std_smpte_314m : e_dv_std_iec_61834);
>
> >From dvsource-alsa.c:
>
>                int apt = (system == &dv_system_625_50) ? 0 : 1;
>
> Here is how libdv determines system:
>
>    dv->system = (header->dsf || (dv_system_50_fields (dv) == 1)) ?
>      e_dv_system_625_50 : e_dv_system_525_60;
>
> dsf field comes from a VAUX header. Here is the core part of
> dv_system_50_fields:
>
>  if ((id = dv -> vaux_pack [0x60]) != 0xff) {
>    if (dv -> vaux_data [id] [2] & 0x20) {
>      return 1;
>    }
>    return 0;
>  }
>
> So, you see it is not real simple. Now, we have to sort through
> dvsource-alsa.c:dv_buffer_fill_dummy() to figure out what is wrong.
>
> Ya know what? I am kind of resenting the fact that myself and others
> have put years of work into libdv, and Roman put years into FFmpeg's
> DV. There's two solid implementations that could have been reused. But
> no, Ben had to go and reinvent the wheel. I don't want to look into
> the finer details of DV again at this time. I already spent enough
> time doing that. I no longer maintain Kino and libdv. Ask Ben to fix
> it.

No prob.  I totally understand.

To Ben's defense his day job is writing ethernet card drivers, and the
video thing is a hobby, so that he doesn't know you already did it,
bla bla...

but like I said... I understand.  and I appreciate what you have done.

-- 
Carl K

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