On Thu, Mar 17, 2016 at 12:50 AM, Mark Thompson <s...@jkqxz.net> wrote:
> On 16/03/16 23:41, Hendrik Leppkes wrote:
>> On Wed, Mar 16, 2016 at 9:37 PM, Mark Thompson <s...@jkqxz.net> wrote:
>>> ---
>>> libavcodec/hevc_parse.c | 14 ++++++++++++++
>>> 1 file changed, 14 insertions(+)
>>>
>>> diff --git a/libavcodec/hevc_parse.c b/libavcodec/hevc_parse.c
>>> index 63ed84a..8c629ff 100644
>>> --- a/libavcodec/hevc_parse.c
>>> +++ b/libavcodec/hevc_parse.c
>>> @@ -227,6 +227,20 @@ int ff_hevc_split_packet(HEVCContext *s, HEVCPacket
>>> *pkt, const uint8_t *buf, in
>>> return AVERROR_INVALIDDATA;
>>> }
>>> } else {
>>> + if (pkt->nals > 0) {
>>> + // Discard arbtrarily many trailing_zero_8bits before the
>>> + // start code of the next NAL unit.
>>> + while (buf[0] == 0 && buf[1] == 0 && buf[2] == 0) {
>>> + ++buf;
>>> + --length;
>>> + if (length < 4)
>>> + break;
>>> + }
>>> + if (length < 4) {
>>> + // There are only zeroes left, so no more NAL units
>>> here.
>>> + break;
>>> + }
>>> + }
>>> /* search start code */
>>> while (buf[0] != 0 || buf[1] != 0 || buf[2] != 1) {
>>> ++buf;
>>
>> I'm slightly confused, wouldn't the loop right after skip over the
>> zeroes until it finds a valid start code?
>> It essentially does the same on a cursory look.
>
> Yes - it doesn't change the scanning process, but it does change the return
> value because in the current code we return failure (and give up on the
> packet entirely) if there aren't any more NAL units to be found.
>
> We actually want to return success if we already have at least one NAL unit
> and then there are zeroes to the end of the packet.
>
Wouldn't it be simpler then to add a condition to the existing loop to
only error out when no NALs exist?
PS: You probably want to check pkt->nb_nals, not pkt->nals, the second
is a memory buffer.
- Hendrik
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