[FFmpeg-devel] [PATCH 2/2] avformat/aviobuf: prefer to use avio_read_partial()

[Marton Balint]

On Fri, 3 Dec 2021, lance.lmwang at gmail.com wrote:

> On Fri, Dec 03, 2021 at 10:47:00AM +0100, Marton Balint wrote:
>>
>>
>> On Fri, 3 Dec 2021, lance.lmwang at gmail.com wrote:
>>
>>> From: Limin Wang <lance.lmwang at gmail.com>
>>>
>>> This is allowed to read fewer bytes than requested. The missing bytes can
>>> be read in the next call.
>>
>> I don't think this is needed, after all we want to read all data, there is
>> no point in reading it in smaller chunks, no?
>
> Now the buf is 1024, in case I'm using sdp file, most of my simple testing sdp is about 300
> byte, so I think it's preferable to use avio_read_partial and let it return directly. as we
> don't expect to read 1024 at all.

I still don't get it. 1024 is the max you will read, nothing will happen 
if the file or the underlying buffer is less than that, so I don't 
understand when you write you want to read it "directly", or what benefit 
it might hold.

avio_read_partial() can be used to reduce latency, but since you want to 
read fixed amount of bytes in avio_read_to_bprint, there is no reason to 
use that.

Regards,
Marton

>
>>
>> Thanks,
>> Marton
>>
>>>
>>> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
>>> ---
>>> libavformat/aviobuf.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
>>> index 14688a2..ebb86e5 100644
>>> --- a/libavformat/aviobuf.c
>>> +++ b/libavformat/aviobuf.c
>>> @@ -1317,7 +1317,7 @@ int avio_read_to_bprint(AVIOContext *h, AVBPrint *pb, size_t max_size)
>>>     int ret;
>>>     char buf[1024];
>>>     while (max_size) {
>>> -        ret = avio_read(h, buf, FFMIN(max_size, sizeof(buf)));
>>> +        ret = avio_read_partial(h, buf, FFMIN(max_size, sizeof(buf)));
>>>         if (ret == AVERROR_EOF)
>>>             return 0;
>>>         if (ret <= 0)
>>> --
>>> 1.8.3.1
>>>
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>
> -- 
> Thanks,
> Limin Wang
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