James Almer:
> On 4/22/2020 9:17 PM, Andreas Rheinhardt wrote:
>> James Almer:
>>> Fixes ticket #8622
>>>
>>> Signed-off-by: James Almer <jamr...@gmail.com>
>>> ---
>>> It fixes it assuming the Picture Timing in that sample is not being
>>> misparsed
>>> by cbs_h265.
>>> We're compliant with the latest revision of the spec, so any
>>> reserved_payload_extension_data found in a sample created today is almost
>>> guaranteed to be bogus. But the spec states that they should be skipped if
>>> found, for forward compatibility reasons.
>>> Would be worth checking if the nvenc encoder is at fault, writing faulty SEI
>>> messages.
>>>
>>> This patch could for that matter make many potential cases of undiscovered
>>> cbs_h265 SEI misparsing be handled as if the remaining bits were these
>>> reserved
>>> bits.
>>
>> That's unfortunately true. I don't see a way to avoid that.
>>
>>>
>>> libavcodec/cbs_h265.h | 1 +
>>> libavcodec/cbs_h265_syntax_template.c | 44 +++++++++++++++++++++++++--
>>> 2 files changed, 43 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/libavcodec/cbs_h265.h b/libavcodec/cbs_h265.h
>>> index 2c1e153ad9..73897f77a4 100644
>>> --- a/libavcodec/cbs_h265.h
>>> +++ b/libavcodec/cbs_h265.h
>>> @@ -715,6 +715,7 @@ typedef struct H265RawSEIPayload {
>>> AVBufferRef *data_ref;
>>> } other;
>>> } payload;
>>> + H265RawExtensionData extension_data;
>>> } H265RawSEIPayload;
>>>
>>> typedef struct H265RawSEI {
>>> diff --git a/libavcodec/cbs_h265_syntax_template.c
>>> b/libavcodec/cbs_h265_syntax_template.c
>>> index f978e16549..ef3254d27f 100644
>>> --- a/libavcodec/cbs_h265_syntax_template.c
>>> +++ b/libavcodec/cbs_h265_syntax_template.c
>>> @@ -2054,11 +2054,43 @@ static int
>>> FUNC(sei_alpha_channel_info)(CodedBitstreamContext *ctx,
>>> return 0;
>>> }
>>>
>>> +static int FUNC(payload_extension)(CodedBitstreamContext *ctx, RWContext
>>> *rw,
>>> + H265RawExtensionData *current, uint32_t
>>> payload_size,
>>> + int cur_pos)
>>> +{
>>> + int err, i;
>>> +
>>> +#ifdef READ
>>> + if (cbs_h265_payload_extension_present(rw, payload_size, cur_pos)) {
>>> + GetBitContext tmp = *rw;
>>> + int payload_zero_bits, bits_left = 8 * payload_size - cur_pos;
>>> + if (bits_left > 8)
>>> + skip_bits_long(&tmp, bits_left - 8);
>>> + payload_zero_bits = ff_ctz(get_bits(&tmp, FFMIN(bits_left, 8)));
>>> + if (payload_zero_bits >= bits_left - 1)
>>> + return AVERROR_INVALIDDATA;
>>> + current->bit_length = bits_left - payload_zero_bits - 1;
>>> + allocate(current->data, (current->bit_length + 7) / 8);
>>> + for (i = 0; i < current->bit_length; i++) {
>>> + uint8_t bit;
>>> + xu(1, reserved_payload_extension_data, bit, 0, 1, 0);
>>> + current->data[i / 8] |= bit << (7 - i % 8);
>>> + }
>>> + }
>>> +#else
>>> + for (i = 0; i < current->bit_length; i++)
>>> + xu(1, reserved_payload_extension_data,
>>> + current->data[i / 8] >> (7 - i % 8) & 1, 0, 1, 0);
>>
>> Do we really need to write one bit at a time? Why not simply one byte at
>> a time and then output the rest in one go? The specs treat it as a
>> bitfield and not as individual bits, so I think we are free to group it
>> as we please.
>
> Mmh, ok.
>
>>
>> The same goes for the other extension_data() function, of course. And
>> for reading.
>
> Doing it for the other function will affect the existing trace output,
> so I'm inclined to leave it as is.
>
>>
>> And shouldn't i be better size_t?
>
> The correct type would be ptrdiff_t, but we never bothered with it and
> always used int.
>
The bit_length field of the extension data struct is size_t. If you
presume that extension data will always only be passed through, then you
are on the safe side; if not, you are not.
>>
>>> +#endif
>>> +
>>> + return 0;
>>> +}
>>> +
>>> static int FUNC(sei_payload)(CodedBitstreamContext *ctx, RWContext *rw,
>>> H265RawSEIPayload *current, int prefix)
>>> {
>>> int err, i;
>>> - int start_position, end_position;
>>> + int start_position, current_position, end_position;
>>>
>>> #ifdef READ
>>> start_position = get_bits_count(rw);
>>> @@ -2122,7 +2154,15 @@ static int FUNC(sei_payload)(CodedBitstreamContext
>>> *ctx, RWContext *rw,
>>> }
>>> }
>>>
>>> - if (byte_alignment(rw)) {
>>> +#ifdef READ
>>> + current_position = get_bits_count(rw) - start_position;
>>> + if (current_position != 8 * current->payload_size) {
>>> +#else
>>> + current_position = put_bits_count(rw) - start_position;
>>> + if (byte_alignment(rw) || current->extension_data.bit_length) {
>>> +#endif
>>> + CHECK(FUNC(payload_extension)(ctx, rw, ¤t->extension_data,
>>> + current->payload_size,
>>> current_position));
>>> fixed(1, bit_equal_to_one, 1);
>>> while (byte_alignment(rw))
>>> fixed(1, bit_equal_to_zero, 0);
>>>
>>
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