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

[Martin Storsjö]

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.

No, that's not how it works.

avio_read_to_bprint loops until it either has read max_size bytes, or 
until it reaches EOF. If you use avio_read_partial, it would only loop 
more times, but it would take the exact same amount of time.

If you read a file from disk, once it has read the 300 bytes of actual 
data, and reach EOF, it returns directly.

avio_read_partial is only relevant for reading data e.g. over a network, 
where there's more data following, but you want to consume and process the 
initially received data before waiting for more. But with 
avio_read_partial it doesn't return until all data has been received 
anyway.

// Martin