[FFmpeg-devel] [PATCH] parser: error out if the codec doesn't match

[Andreas Cadhalpun]

On 05.01.2016 11:46, Michael Niedermayer wrote:
> On Tue, Jan 05, 2016 at 12:44:40AM +0100, Andreas Cadhalpun wrote:
>> Otherwise this can have some surprising effects (crashes), so let's
>> better not allow it.
>>
>> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
>> ---
>>  libavcodec/parser.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/libavcodec/parser.c b/libavcodec/parser.c
>> index 2809158..1f38edb 100644
>> --- a/libavcodec/parser.c
>> +++ b/libavcodec/parser.c
>> @@ -141,6 +141,17 @@ int av_parser_parse2(AVCodecParserContext *s, AVCodecContext *avctx,
>>      int index, i;
>>      uint8_t dummy_buf[AV_INPUT_BUFFER_PADDING_SIZE];
>>  
>> +    if (avctx->codec_id != s->parser->codec_ids[0] &&
>> +        avctx->codec_id != s->parser->codec_ids[1] &&
>> +        avctx->codec_id != s->parser->codec_ids[2] &&
>> +        avctx->codec_id != s->parser->codec_ids[3] &&
>> +        avctx->codec_id != s->parser->codec_ids[4]) {
>> +        av_log(avctx, AV_LOG_ERROR,
>> +               "The parser doesn't match the codec %s.\n",
>> +               avcodec_get_name(avctx->codec_id));
>> +        return buf_size;
>> +    }
> 
> does it also work to check if a parser is set when the codec id
> is changed ? as in below

That wouldn't work, as the codec id wasn't changed in force_codec_ids,
but in the API using program.
To reiterate, the problematic steps were:
 * call avformat_find_stream_info, which detects a codec and initializes
   a parser for it
 * afterwards change the codec id in the API using program, so it
   doesn't match with the parser

Thus I think the only reliable way to detect this is a check in av_parser_parse2.

> (that would avoid doing 5 extra checks per packet)

Parsers aren't that speed critical code, I think.

Best regards,
Andreas