[libdvbpsi-devel] [PATCH] Fix a parsing error in dr_02.c

[Daniel Kamil Kozar]

Jean-Paul,
Of course, you're right. Sorry about the unnecessary confusion. The
decoding part is in fact correct : it's the generating that doesn't
set the flag correctly, which is why the tests in 'misc' failed on me
after running them. I'll post a patch shortly.

Daniel

On 1 June 2015 at 10:16, Jean-Paul Saman <jpsaman at videolan.org> wrote:
>
> On Mon, Jun 1, 2015 at 9:48 AM, Jean-Paul Saman <jpsaman at videolan.org>
> wrote:
>>
>> Daniel,
>>
>> On Sun, May 31, 2015 at 10:03 PM, Daniel Kamil Kozar <dkk089 at gmail.com>
>> wrote:
>>>
>>> b_mpeg2 in dvbpsi_vstream_dr_t corresponds to what the H.222.0 refers to
>>> as the "MPEG_1_only_flag". If the flag is not set, it means that no
>>> extra data is contained at the end of the descriptor. The code in
>>> dr_02.c did exactly the opposite.
>>> ---
>>>  src/descriptors/dr_02.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/src/descriptors/dr_02.c b/src/descriptors/dr_02.c
>>> index 774a1c0..1c35d83 100644
>>> --- a/src/descriptors/dr_02.c
>>> +++ b/src/descriptors/dr_02.c
>>> @@ -60,7 +60,7 @@ dvbpsi_vstream_dr_t *
>>> dvbpsi_DecodeVStreamDr(dvbpsi_descriptor_t * p_descriptor)
>>>    if(!p_decoded) return NULL;
>>>
>>>    /* Decode data and check the length */
>>> -  p_decoded->b_mpeg2 = !((p_descriptor->p_data[0] & 0x04) ? true :
>>> false);
>>> +  p_decoded->b_mpeg2 = (p_descriptor->p_data[0] & 0x04) ? true : false;
>>>    if(    (!p_decoded->b_mpeg2 && (p_descriptor->i_length != 1))
>>>        || (p_decoded->b_mpeg2 && (p_descriptor->i_length != 3)))
>>>    {
>>> --
>>> 2.4.2
>>>
>>
>> Could you double check the specs, because it would mean a revert of
>> 25cdb9fd, which I believe is correct in the mentioned specs.
>> That H.222.0 and " ISO/IEC 13818-1 : 2000, table 2-40 and 2.6.3"
>> contradict each other is quite unlikely IMHO.
>>
>> $> git show 25cdb9fd
>> commit 25cdb9fd7ce804ec69b91fa1b0887435c474b32d
>> Author: Jean-Baptiste Kempf <jb at videolan.org>
>> Date:   Tue Aug 12 04:04:47 2014 +0200
>>
>>     Correctly flag mpeg2 video data in video_stream_descriptor
>>
>>     See ISO/IEC 13818-1 : 2000, table 2-40 and 2.6.3
>>
>>     See https://trac.videolan.org/vlc/ticket/4200
>>
>>     Signed-off-by: Jean-Paul Saman <jpsaman at videolan.org>
>>
>> diff --git a/src/descriptors/dr_02.c b/src/descriptors/dr_02.c
>> index 1c35d83..774a1c0 100644
>> --- a/src/descriptors/dr_02.c
>> +++ b/src/descriptors/dr_02.c
>> @@ -60,7 +60,7 @@ dvbpsi_vstream_dr_t *
>> dvbpsi_DecodeVStreamDr(dvbpsi_descriptor_t * p_descriptor)
>>    if(!p_decoded) return NULL;
>>
>>    /* Decode data and check the length */
>> -  p_decoded->b_mpeg2 = (p_descriptor->p_data[0] & 0x04) ? true : false;
>> +  p_decoded->b_mpeg2 = !((p_descriptor->p_data[0] & 0x04) ? true :
>> false);
>>    if(    (!p_decoded->b_mpeg2 && (p_descriptor->i_length != 1))
>>        || (p_decoded->b_mpeg2 && (p_descriptor->i_length != 3)))
>>    {
>
>
> H.222.0 page 65 says:
>
> "MPEG_1_only_flag – This is a 1-bit field which when set to '1' indicates
> that the video stream contains only
> ISO/IEC 11172-2 data. If set to '0' the video stream may contain both ITU-T
> Rec. H.262 | ISO/IEC 13818-2 video data
> and constrained parameter ISO/IEC 11172-2 video data."
>
> Meaning that if this flag is '0', then there is extra data. If we now
> translate that to b_mpeg2 boolean in libdvbpsi, then it means that
> b_mpeg2 should be the inverse of the MPEG_1_only_flag, or b_mpeg2 =
> !(MPEG_1_only_flag).
>
> On bit level that becomes:
> (p_data[0] & 0x04) => 0 when the flag is not set, thus extra data and
> variable p_decoded->b_mpeg2 should become true
> (p_data[0] & 0x04) => 1 when the flag is set, thus mpeg1 only data and
> variable p_decoded->b_mpeg2 should become false
>
> Hence I believe the current code is correct, since that is exactly what
> happens now.
>
>>
>> Kind regards,
>>
>> Jean-Paul Saman
>>>
>>> _______________________________________________
>>> libdvbpsi-devel mailing list
>>> libdvbpsi-devel at videolan.org
>>> https://mailman.videolan.org/listinfo/libdvbpsi-devel
>>
>>
>