[vlc-devel] [PATCH] flac: move CRC update into STATE_NEXT_SYNC

[Rafaël Carré]

Le 09/12/2013 13:47, Tristan Matthews a écrit :
> On Fri, Dec 6, 2013 at 10:50 AM, Rafaël Carré <funman at videolan.org> wrote:
>> Le 06/12/2013 16:07, Tristan Matthews a écrit :
>>> Fixes #9966.
>>> ---
>>>  modules/packetizer/flac.c | 9 ++++++---
>>>  1 file changed, 6 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/modules/packetizer/flac.c b/modules/packetizer/flac.c
>>> index 2f16717..b5af285 100644
>>> --- a/modules/packetizer/flac.c
>>> +++ b/modules/packetizer/flac.c
>>> @@ -572,6 +572,11 @@ static block_t *Packetize(decoder_t *p_dec, block_t **pp_block)
>>>          p_sys->i_frame_size = p_sys->b_stream_info && p_sys->stream_info.min_framesize > 0 ?
>>>                                                          p_sys->stream_info.min_framesize : 1;
>>>
>>> +    case STATE_NEXT_SYNC:
>>> +        /* TODO: If pp_block == NULL, flush the buffer without checking the
>>> +         * next sync word */
>>> +
>>> +    {
>>
>> Looks good, but won't this calculate the crc for each incoming packet
>> needed until we reach the next sync?
> 
> Do you mean, will this lead to more crc calculations than before?

Yes, although I am just guessing that this might be significant (I did
not benchmark it).

>> Not sure if there's an easy way around this without changing
>> block_helper.h though
> 
> What would need to be changed in block_helper, a function to do partial reads?

I don't know yet :/

I guess we need to spend some time thinking about it.

> Best,
> Tristan
> 
>>>          /* Calculate the initial CRC for the minimal frame size,
>>>           * We'll update it as we look for the next start code. */
>>>          uint8_t *buf = malloc(p_sys->i_frame_size);
>>> @@ -588,10 +593,8 @@ static block_t *Packetize(decoder_t *p_dec, block_t **pp_block)
>>>              crc = flac_crc16(crc, buf[i]);
>>>          free(buf);
>>>          p_sys->crc = crc;
>>> +    }
>>>
>>> -    case STATE_NEXT_SYNC:
>>> -        /* TODO: If pp_block == NULL, flush the buffer without checking the
>>> -         * next sync word */
>>>
>>>          /* Check if next expected frame contains the sync word */
>>>          while (!block_PeekOffsetBytes(&p_sys->bytestream, p_sys->i_frame_size,