avformat: add format_probesize to allow tuning the maximum amount of bytes to identify the filetype

Currently probesize is cliped at 1mb before being used for format detection.
Alternatively this cliping could be removed but this would then tie various
things like stream analysis to the file detection.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -1523,6 +1523,13 @@ typedef struct AVFormatContext {
      */
     int probe_score;
 
+    /**
+     * number of bytes to read maximally to identify format.
+     * - encoding: unused
+     * - decoding: set by user through AVOPtions (NO direct access)
+     */
+    int format_probesize;
+
     /*****************************************************************
      * All fields below this line are not part of the public API. They
      * may not be used outside of libavformat and can be changed and

libavformat/options_table.h

@@ -25,6 +25,7 @@
 
 #include "libavutil/opt.h"
 #include "avformat.h"
+#include "internal.h"
 
 #define OFFSET(x) offsetof(AVFormatContext,x)
 #define DEFAULT 0 //should be NAN but it does not work as it is not a constant in glibc as required by ANSI/ISO C
@@ -36,6 +37,7 @@ static const AVOption avformat_options[] = {
 {"avioflags", NULL, OFFSET(avio_flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "avioflags"},
 {"direct", "reduce buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVIO_FLAG_DIRECT }, INT_MIN, INT_MAX, D|E, "avioflags"},
 {"probesize", "set probing size", OFFSET(probesize), AV_OPT_TYPE_INT, {.i64 = 5000000 }, 32, INT_MAX, D},
+{"formatprobesize", "number of bytes to probe file format", OFFSET(format_probesize), AV_OPT_TYPE_INT, {.i64 = PROBE_BUF_MAX}, 0, INT_MAX-1, D},
 {"packetsize", "set packet size", OFFSET(packet_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, E},
 {"fflags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = AVFMT_FLAG_FLUSH_PACKETS }, INT_MIN, INT_MAX, D|E, "fflags"},
 {"flush_packets", "reduce the latency by flushing out packets immediately", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_FLUSH_PACKETS }, INT_MIN, INT_MAX, D, "fflags"},

libavformat/utils.c

@@ -379,8 +379,6 @@ int av_probe_input_buffer2(AVIOContext *pb, AVInputFormat **fmt,
 
     if (!max_probe_size)
         max_probe_size = PROBE_BUF_MAX;
-    else if (max_probe_size > PROBE_BUF_MAX)
-        max_probe_size = PROBE_BUF_MAX;
     else if (max_probe_size < PROBE_BUF_MIN) {
         av_log(logctx, AV_LOG_ERROR,
                "Specified probe size value %u cannot be < %u\n", max_probe_size, PROBE_BUF_MIN);
@@ -474,7 +472,7 @@ static int init_input(AVFormatContext *s, const char *filename,
         s->flags |= AVFMT_FLAG_CUSTOM_IO;
         if (!s->iformat)
             return av_probe_input_buffer2(s->pb, &s->iformat, filename,
-                                         s, 0, s->probesize);
+                                         s, 0, s->format_probesize);
         else if (s->iformat->flags & AVFMT_NOFILE)
             av_log(s, AV_LOG_WARNING, "Custom AVIOContext makes no sense and "
                                       "will be ignored with AVFMT_NOFILE format.\n");
@@ -491,7 +489,7 @@ static int init_input(AVFormatContext *s, const char *filename,
     if (s->iformat)
         return 0;
     return av_probe_input_buffer2(s->pb, &s->iformat, filename,
-                                 s, 0, s->probesize);
+                                 s, 0, s->format_probesize);
 }
 
 static AVPacket *add_to_pktbuf(AVPacketList **packet_buffer, AVPacket *pkt,