cli: Use memory-mapped input frames for yuv and y4m

Improves performance by avoiding extraneous memory copying.
Most beneficial on fast settings.

On average around 5-10% faster overall on ultrafast but the
performance improvement can be even larger in some cases.

configure

@@ -373,7 +373,7 @@ NL="
 # list of all preprocessor HAVE values we can define
 CONFIG_HAVE="MALLOC_H ALTIVEC ALTIVEC_H MMX ARMV6 ARMV6T2 NEON BEOSTHREAD POSIXTHREAD WIN32THREAD THREAD LOG2F SWSCALE \
              LAVF FFMS GPAC AVS GPL VECTOREXT INTERLACED CPU_COUNT OPENCL THP LSMASH X86_INLINE_ASM AS_FUNC INTEL_DISPATCHER \
-             MSA"
+             MSA MMAP"
 
 # parse options
 
@@ -968,6 +968,10 @@ if cc_check "math.h" "-Werror" "return log2f(2);" ; then
     define HAVE_LOG2F
 fi
 
+if [ "$SYS" != "WINDOWS" ] && cpp_check "sys/mman.h unistd.h" "" "defined(MAP_PRIVATE)"; then
+    define HAVE_MMAP
+fi
+
 if [ "$SYS" = "LINUX" -a \( "$ARCH" = "X86" -o "$ARCH" = "X86_64" \) ] && cc_check "sys/mman.h" "" "MADV_HUGEPAGE;" ; then
     define HAVE_THP
 fi

filters/video/source.c

@@ -44,7 +44,7 @@ static int init( hnd_t *handle, cli_vid_filter_t *filter, video_info_t *info, x2
         return -1;
     h->cur_frame = -1;
 
-    if( cli_input.picture_alloc( &h->pic, info->csp, info->width, info->height ) )
+    if( cli_input.picture_alloc( &h->pic, *handle, info->csp, info->width, info->height ) )
         return -1;
 
     h->hin = *handle;
@@ -76,7 +76,7 @@ static int release_frame( hnd_t handle, cli_pic_t *pic, int frame )
 static void free_filter( hnd_t handle )
 {
     source_hnd_t *h = handle;
-    cli_input.picture_clean( &h->pic );
+    cli_input.picture_clean( &h->pic, h->hin );
     cli_input.close_file( h->hin );
     free( h );
 }

input/avs.c

@@ -357,7 +357,7 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
     return 0;
 }
 
-static int picture_alloc( cli_pic_t *pic, int csp, int width, int height )
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
 {
     if( x264_cli_pic_alloc( pic, X264_CSP_NONE, width, height ) )
         return -1;
@@ -399,7 +399,7 @@ static int release_frame( cli_pic_t *pic, hnd_t handle )
     return 0;
 }
 
-static void picture_clean( cli_pic_t *pic )
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
 {
     memset( pic, 0, sizeof(cli_pic_t) );
 }

input/ffms.c

@@ -175,7 +175,7 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
     return 0;
 }
 
-static int picture_alloc( cli_pic_t *pic, int csp, int width, int height )
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
 {
     if( x264_cli_pic_alloc( pic, X264_CSP_NONE, width, height ) )
         return -1;
@@ -209,7 +209,7 @@ static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
     return 0;
 }
 
-static void picture_clean( cli_pic_t *pic )
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
 {
     memset( pic, 0, sizeof(cli_pic_t) );
 }

input/input.c

@@ -4,6 +4,7 @@
  * Copyright (C) 2010-2015 x264 project
  *
  * Authors: Steven Walters <kemuri9@gmail.com>
+ *          Henrik Gramner <henrik@gramner.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -25,6 +26,14 @@
 
 #include "input.h"
 
+#ifdef _WIN32
+#include <io.h>
+#include <windows.h>
+#elif HAVE_MMAP
+#include <sys/mman.h>
+#include <unistd.h>
+#endif
+
 const x264_cli_csp_t x264_cli_csps[] = {
     [X264_CSP_I420] = { "i420", 3, { 1, .5, .5 }, { 1, .5, .5 }, 2, 2 },
     [X264_CSP_I422] = { "i422", 3, { 1, .5, .5 }, { 1,  1,  1 }, 2, 1 },
@@ -76,7 +85,7 @@ uint64_t x264_cli_pic_size( int csp, int width, int height )
     return size;
 }
 
-static int x264_cli_pic_alloc_internal( cli_pic_t *pic, int csp, int width, int height, int align )
+static int x264_cli_pic_init_internal( cli_pic_t *pic, int csp, int width, int height, int align, int alloc )
 {
     memset( pic, 0, sizeof(cli_pic_t) );
     int csp_mask = csp & X264_CSP_MASK;
@@ -92,11 +101,15 @@ static int x264_cli_pic_alloc_internal( cli_pic_t *pic, int csp, int width, int
         int stride = width * x264_cli_csps[csp_mask].width[i];
         stride *= x264_cli_csp_depth_factor( csp );
         stride = ALIGN( stride, align );
-        uint64_t size = (uint64_t)(height * x264_cli_csps[csp_mask].height[i]) * stride;
-        pic->img.plane[i] = x264_malloc( size );
-        if( !pic->img.plane[i] )
-            return -1;
         pic->img.stride[i] = stride;
+
+        if( alloc )
+        {
+            size_t size = (size_t)(height * x264_cli_csps[csp_mask].height[i]) * stride;
+            pic->img.plane[i] = x264_malloc( size );
+            if( !pic->img.plane[i] )
+                return -1;
+        }
     }
 
     return 0;
@@ -104,12 +117,17 @@ static int x264_cli_pic_alloc_internal( cli_pic_t *pic, int csp, int width, int
 
 int x264_cli_pic_alloc( cli_pic_t *pic, int csp, int width, int height )
 {
-    return x264_cli_pic_alloc_internal( pic, csp, width, height, 1 );
+    return x264_cli_pic_init_internal( pic, csp, width, height, 1, 1 );
 }
 
 int x264_cli_pic_alloc_aligned( cli_pic_t *pic, int csp, int width, int height )
 {
-    return x264_cli_pic_alloc_internal( pic, csp, width, height, NATIVE_ALIGN );
+    return x264_cli_pic_init_internal( pic, csp, width, height, NATIVE_ALIGN, 1 );
+}
+
+int x264_cli_pic_init_noalloc( cli_pic_t *pic, int csp, int width, int height )
+{
+    return x264_cli_pic_init_internal( pic, csp, width, height, 1, 0 );
 }
 
 void x264_cli_pic_clean( cli_pic_t *pic )
@@ -125,3 +143,75 @@ const x264_cli_csp_t *x264_cli_get_csp( int csp )
         return NULL;
     return x264_cli_csps + (csp&X264_CSP_MASK);
 }
+
+/* Functions for handling memory-mapped input frames */
+int x264_cli_mmap_init( cli_mmap_t *h, FILE *fh )
+{
+#ifdef _WIN32
+    HANDLE osfhandle = (HANDLE)_get_osfhandle( _fileno( fh ) );
+    if( osfhandle != INVALID_HANDLE_VALUE )
+    {
+        SYSTEM_INFO si;
+        GetSystemInfo( &si );
+        h->align_mask = si.dwAllocationGranularity - 1;
+        h->map_handle = CreateFileMappingW( osfhandle, NULL, PAGE_READONLY, 0, 0, NULL );
+        return !h->map_handle;
+    }
+#elif HAVE_MMAP && defined(_SC_PAGESIZE)
+    h->align_mask = sysconf( _SC_PAGESIZE ) - 1;
+    h->fd = fileno( fh );
+    return h->align_mask < 0 || h->fd < 0;
+#endif
+    return -1;
+}
+
+void *x264_cli_mmap( cli_mmap_t *h, int64_t offset, size_t size )
+{
+#if defined(_WIN32) || HAVE_MMAP
+    int align = offset & h->align_mask;
+    offset -= align;
+    size   += align;
+#ifdef _WIN32
+    uint8_t *base = MapViewOfFile( h->map_handle, FILE_MAP_READ, offset >> 32, offset, size );
+    /* TODO: Would PrefetchVirtualMemory() (only available on Win8+) be beneficial? */
+    if( base )
+        return base + align;
+#else
+    uint8_t *base = mmap( NULL, size, PROT_READ, MAP_PRIVATE, h->fd, offset );
+    if( base != MAP_FAILED )
+    {
+        /* Ask the OS to readahead pages. This improves performance whereas
+         * forcing page faults by manually accessing every page does not.
+         * Some systems have implemented madvise() but not posix_madvise()
+         * and vice versa, so check both to see if either is available. */
+#ifdef MADV_WILLNEED
+        madvise( base, size, MADV_WILLNEED );
+#elif defined(POSIX_MADV_WILLNEED)
+        posix_madvise( base, size, POSIX_MADV_WILLNEED );
+#endif
+        return base + align;
+    }
+#endif
+#endif
+    return NULL;
+}
+
+int x264_cli_munmap( cli_mmap_t *h, void *addr, size_t size )
+{
+#if defined(_WIN32) || HAVE_MMAP
+    void *base = (void*)((intptr_t)addr & ~h->align_mask);
+#ifdef _WIN32
+    return !UnmapViewOfFile( base );
+#else
+    return munmap( base, size + (intptr_t)addr - (intptr_t)base );
+#endif
+#endif
+    return -1;
+}
+
+void x264_cli_mmap_close( cli_mmap_t *h )
+{
+#ifdef _WIN32
+    CloseHandle( h->map_handle );
+#endif
+}

input/input.h

@@ -88,20 +88,20 @@ typedef struct
 typedef struct
 {
     int (*open_file)( char *psz_filename, hnd_t *p_handle, video_info_t *info, cli_input_opt_t *opt );
-    int (*picture_alloc)( cli_pic_t *pic, int csp, int width, int height );
+    int (*picture_alloc)( cli_pic_t *pic, hnd_t handle, int csp, int width, int height );
     int (*read_frame)( cli_pic_t *pic, hnd_t handle, int i_frame );
     int (*release_frame)( cli_pic_t *pic, hnd_t handle );
-    void (*picture_clean)( cli_pic_t *pic );
+    void (*picture_clean)( cli_pic_t *pic, hnd_t handle );
     int (*close_file)( hnd_t handle );
 } cli_input_t;
 
 extern const cli_input_t raw_input;
 extern const cli_input_t y4m_input;
 extern const cli_input_t avs_input;
-extern cli_input_t thread_input;
+extern const cli_input_t thread_input;
 extern const cli_input_t lavf_input;
 extern const cli_input_t ffms_input;
-extern cli_input_t timecode_input;
+extern const cli_input_t timecode_input;
 
 extern cli_input_t cli_input;
 
@@ -125,9 +125,25 @@ int      x264_cli_csp_is_invalid( int csp );
 int      x264_cli_csp_depth_factor( int csp );
 int      x264_cli_pic_alloc( cli_pic_t *pic, int csp, int width, int height );
 int      x264_cli_pic_alloc_aligned( cli_pic_t *pic, int csp, int width, int height );
+int      x264_cli_pic_init_noalloc( cli_pic_t *pic, int csp, int width, int height );
 void     x264_cli_pic_clean( cli_pic_t *pic );
 uint64_t x264_cli_pic_plane_size( int csp, int width, int height, int plane );
 uint64_t x264_cli_pic_size( int csp, int width, int height );
 const x264_cli_csp_t *x264_cli_get_csp( int csp );
 
+typedef struct
+{
+    int align_mask;
+#ifdef _WIN32
+    void *map_handle;
+#elif HAVE_MMAP
+    int fd;
+#endif
+} cli_mmap_t;
+
+int x264_cli_mmap_init( cli_mmap_t *h, FILE *fh );
+void *x264_cli_mmap( cli_mmap_t *h, int64_t offset, size_t size );
+int x264_cli_munmap( cli_mmap_t *h, void *addr, size_t size );
+void x264_cli_mmap_close( cli_mmap_t *h );
+
 #endif

input/lavf.c

@@ -65,7 +65,7 @@ static int read_frame_internal( cli_pic_t *p_pic, lavf_hnd_t *h, int i_frame, vi
             XCHG( cli_image_t, p_pic->img, h->first_pic->img );
             p_pic->pts = h->first_pic->pts;
         }
-        lavf_input.picture_clean( h->first_pic );
+        lavf_input.picture_clean( h->first_pic, h );
         free( h->first_pic );
         h->first_pic = NULL;
         if( !i_frame )
@@ -192,7 +192,7 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
 
     /* prefetch the first frame and set/confirm flags */
     h->first_pic = malloc( sizeof(cli_pic_t) );
-    FAIL_IF_ERROR( !h->first_pic || lavf_input.picture_alloc( h->first_pic, X264_CSP_OTHER, info->width, info->height ),
+    FAIL_IF_ERROR( !h->first_pic || lavf_input.picture_alloc( h->first_pic, h, X264_CSP_OTHER, info->width, info->height ),
                    "malloc failed\n" )
     else if( read_frame_internal( h->first_pic, h, 0, info ) )
         return -1;
@@ -215,7 +215,7 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
     return 0;
 }
 
-static int picture_alloc( cli_pic_t *pic, int csp, int width, int height )
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
 {
     if( x264_cli_pic_alloc( pic, X264_CSP_NONE, width, height ) )
         return -1;
@@ -229,7 +229,7 @@ static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
     return read_frame_internal( pic, handle, i_frame, NULL );
 }
 
-static void picture_clean( cli_pic_t *pic )
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
 {
     memset( pic, 0, sizeof(cli_pic_t) );
 }

input/raw.c

@@ -35,6 +35,8 @@ typedef struct
     uint64_t plane_size[4];
     uint64_t frame_size;
     int bit_depth;
+    cli_mmap_t mmap;
+    int use_mmap;
 } raw_hnd_t;
 
 static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, cli_input_opt_t *opt )
@@ -96,6 +98,10 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
         uint64_t size = ftell( h->fh );
         fseek( h->fh, 0, SEEK_SET );
         info->num_frames = size / h->frame_size;
+
+        /* Attempt to use memory-mapped input frames if possible */
+        if( !(h->bit_depth & 7) )
+            h->use_mmap = !x264_cli_mmap_init( &h->mmap, h->fh );
     }
 
     *p_handle = h;
@@ -104,11 +110,18 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
 
 static int read_frame_internal( cli_pic_t *pic, raw_hnd_t *h, int bit_depth_uc )
 {
-    int error = 0;
     int pixel_depth = x264_cli_csp_depth_factor( pic->img.csp );
-    for( int i = 0; i < pic->img.planes && !error; i++ )
+
+    for( int i = 0; i < pic->img.planes; i++ )
     {
-        error |= fread( pic->img.plane[i], pixel_depth, h->plane_size[i], h->fh ) != h->plane_size[i];
+        if( h->use_mmap )
+        {
+            if( i )
+                pic->img.plane[i] = pic->img.plane[i-1] + pixel_depth * h->plane_size[i-1];
+        }
+        else if( fread( pic->img.plane[i], pixel_depth, h->plane_size[i], h->fh ) != h->plane_size[i] )
+            return -1;
+
         if( bit_depth_uc )
         {
             /* upconvert non 16bit high depth planes to 16bit using the same
@@ -120,14 +133,20 @@ static int read_frame_internal( cli_pic_t *pic, raw_hnd_t *h, int bit_depth_uc )
                 plane[j] = plane[j] << lshift;
         }
     }
-    return error;
+    return 0;
 }
 
 static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
 {
     raw_hnd_t *h = handle;
 
-    if( i_frame > h->next_frame )
+    if( h->use_mmap )
+    {
+        pic->img.plane[0] = x264_cli_mmap( &h->mmap, i_frame * h->frame_size, h->frame_size );
+        if( !pic->img.plane[0] )
+            return -1;
+    }
+    else if( i_frame > h->next_frame )
     {
         if( x264_is_regular_file( h->fh ) )
             fseek( h->fh, i_frame * h->frame_size, SEEK_SET );
@@ -147,14 +166,39 @@ static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
     return 0;
 }
 
+static int release_frame( cli_pic_t *pic, hnd_t handle )
+{
+    raw_hnd_t *h = handle;
+    if( h->use_mmap )
+        return x264_cli_munmap( &h->mmap, pic->img.plane[0], h->frame_size );
+    return 0;
+}
+
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
+{
+    raw_hnd_t *h = handle;
+    return (h->use_mmap ? x264_cli_pic_init_noalloc : x264_cli_pic_alloc)( pic, csp, width, height );
+}
+
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
+{
+    raw_hnd_t *h = handle;
+    if( h->use_mmap )
+        memset( pic, 0, sizeof(cli_pic_t) );
+    else
+        x264_cli_pic_clean( pic );
+}
+
 static int close_file( hnd_t handle )
 {
     raw_hnd_t *h = handle;
     if( !h || !h->fh )
         return 0;
+    if( h->use_mmap )
+        x264_cli_mmap_close( &h->mmap );
     fclose( h->fh );
     free( h );
     return 0;
 }
 
-const cli_input_t raw_input = { open_file, x264_cli_pic_alloc, read_frame, NULL, x264_cli_pic_clean, close_file };
+const cli_input_t raw_input = { open_file, picture_alloc, read_frame, release_frame, picture_clean, close_file };

input/thread.c

@@ -48,7 +48,7 @@ typedef struct thread_input_arg_t
 static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, cli_input_opt_t *opt )
 {
     thread_hnd_t *h = malloc( sizeof(thread_hnd_t) );
-    FAIL_IF_ERR( !h || cli_input.picture_alloc( &h->pic, info->csp, info->width, info->height ),
+    FAIL_IF_ERR( !h || cli_input.picture_alloc( &h->pic, *p_handle, info->csp, info->width, info->height ),
                  "x264", "malloc failed\n" )
     h->input = cli_input;
     h->p_handle = *p_handle;
@@ -59,8 +59,6 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
     h->next_args->h = h;
     h->next_args->status = 0;
     h->frame_total = info->num_frames;
-    thread_input.picture_alloc = h->input.picture_alloc;
-    thread_input.picture_clean = h->input.picture_clean;
 
     if( x264_threadpool_init( &h->pool, 1, NULL, NULL ) )
         return -1;
@@ -115,15 +113,27 @@ static int release_frame( cli_pic_t *pic, hnd_t handle )
     return 0;
 }
 
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
+{
+    thread_hnd_t *h = handle;
+    return h->input.picture_alloc( pic, h->p_handle, csp, width, height );
+}
+
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
+{
+    thread_hnd_t *h = handle;
+    h->input.picture_clean( pic, h->p_handle );
+}
+
 static int close_file( hnd_t handle )
 {
     thread_hnd_t *h = handle;
     x264_threadpool_delete( h->pool );
+    h->input.picture_clean( &h->pic, h->p_handle );
     h->input.close_file( h->p_handle );
-    h->input.picture_clean( &h->pic );
     free( h->next_args );
     free( h );
     return 0;
 }
 
-cli_input_t thread_input = { open_file, NULL, read_frame, release_frame, NULL, close_file };
+const cli_input_t thread_input = { open_file, picture_alloc, read_frame, release_frame, picture_clean, close_file };

input/timecode.c

@@ -365,8 +365,6 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
         h->timebase_num = info->fps_den; /* can be changed later by auto timebase generation */
     if( h->auto_timebase_den )
         h->timebase_den = 0;             /* set later by auto timebase generation */
-    timecode_input.picture_alloc = h->input.picture_alloc;
-    timecode_input.picture_clean = h->input.picture_clean;
 
     tcfile_in = x264_fopen( psz_filename, "rb" );
     FAIL_IF_ERROR( !tcfile_in, "can't open `%s'\n", psz_filename )
@@ -434,6 +432,18 @@ static int release_frame( cli_pic_t *pic, hnd_t handle )
     return 0;
 }
 
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
+{
+    timecode_hnd_t *h = handle;
+    return h->input.picture_alloc( pic, h->p_handle, csp, width, height );
+}
+
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
+{
+    timecode_hnd_t *h = handle;
+    h->input.picture_clean( pic, h->p_handle );
+}
+
 static int close_file( hnd_t handle )
 {
     timecode_hnd_t *h = handle;
@@ -444,4 +454,4 @@ static int close_file( hnd_t handle )
     return 0;
 }
 
-cli_input_t timecode_input = { open_file, NULL, read_frame, release_frame, NULL, close_file };
+const cli_input_t timecode_input = { open_file, picture_alloc, read_frame, release_frame, picture_clean, close_file };

input/y4m.c

@@ -36,6 +36,8 @@ typedef struct
     uint64_t frame_size;
     uint64_t plane_size[3];
     int bit_depth;
+    cli_mmap_t mmap;
+    int use_mmap;
 } y4m_hnd_t;
 
 #define Y4M_MAGIC "YUV4MPEG2"
@@ -97,8 +99,8 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
             break;
         }
     }
-    if( i == MAX_YUV4_HEADER || strncmp( header, Y4M_MAGIC, sizeof(Y4M_MAGIC)-1 ) )
-        return -1;
+    FAIL_IF_ERROR( strncmp( header, Y4M_MAGIC, sizeof(Y4M_MAGIC)-1 ), "bad sequence header magic\n" )
+    FAIL_IF_ERROR( i == MAX_YUV4_HEADER, "bad sequence header length\n" )
 
     /* Scan properties */
     header_end = &header[i+1]; /* Include space */
@@ -221,6 +223,10 @@ static int open_file( char *psz_filename, hnd_t *p_handle, video_info_t *info, c
         uint64_t i_size = ftell( h->fh );
         fseek( h->fh, init_pos, SEEK_SET );
         info->num_frames = (i_size - h->seq_header_len) / h->frame_size;
+
+        /* Attempt to use memory-mapped input frames if possible */
+        if( !(h->bit_depth & 7) )
+            h->use_mmap = !x264_cli_mmap_init( &h->mmap, h->fh );
     }
 
     *p_handle = h;
@@ -231,26 +237,44 @@ static int read_frame_internal( cli_pic_t *pic, y4m_hnd_t *h, int bit_depth_uc )
 {
     static const size_t slen = sizeof(Y4M_FRAME_MAGIC)-1;
     int pixel_depth = x264_cli_csp_depth_factor( pic->img.csp );
-    int i = 0;
-    char header[16];
+    int i = sizeof(Y4M_FRAME_MAGIC);
+    char header_buf[16];
+    char *header;
 
-    /* Read frame header - without terminating '\n' */
-    if( fread( header, 1, slen, h->fh ) != slen )
-        return -1;
-
-    header[slen] = 0;
-    FAIL_IF_ERROR( strncmp( header, Y4M_FRAME_MAGIC, slen ), "bad header magic (%"PRIx32" <=> %s)\n",
-                   M32(header), header )
-
-    /* Skip most of it */
-    while( i < MAX_FRAME_HEADER && fgetc( h->fh ) != '\n' )
-        i++;
-    FAIL_IF_ERROR( i == MAX_FRAME_HEADER, "bad frame header!\n" )
-
-    int error = 0;
-    for( i = 0; i < pic->img.planes && !error; i++ )
+    /* Verify that the frame header is valid */
+    if( h->use_mmap )
     {
-        error |= fread( pic->img.plane[i], pixel_depth, h->plane_size[i], h->fh ) != h->plane_size[i];
+        header = (char*)pic->img.plane[0];
+        pic->img.plane[0] += h->frame_header_len;
+
+        /* If the header length has changed between frames the size of the mapping will be invalid.
+         * It might be possible to work around it, but I'm not aware of any tool beside fuzzers that
+         * produces y4m files with variable-length frame headers so just error out if that happens. */
+        while( i <= h->frame_header_len && header[i-1] != '\n' )
+            i++;
+        FAIL_IF_ERROR( i != h->frame_header_len, "bad frame header length\n" )
+    }
+    else
+    {
+        header = header_buf;
+        if( fread( header, 1, slen, h->fh ) != slen )
+            return -1;
+        while( i <= MAX_FRAME_HEADER && fgetc( h->fh ) != '\n' )
+            i++;
+        FAIL_IF_ERROR( i > MAX_FRAME_HEADER, "bad frame header length\n" )
+    }
+    FAIL_IF_ERROR( memcmp( header, Y4M_FRAME_MAGIC, slen ), "bad frame header magic\n" )
+
+    for( i = 0; i < pic->img.planes; i++ )
+    {
+        if( h->use_mmap )
+        {
+            if( i )
+                pic->img.plane[i] = pic->img.plane[i-1] + pixel_depth * h->plane_size[i-1];
+        }
+        else if( fread( pic->img.plane[i], pixel_depth, h->plane_size[i], h->fh ) != h->plane_size[i] )
+            return -1;
+
         if( bit_depth_uc )
         {
             /* upconvert non 16bit high depth planes to 16bit using the same
@@ -262,14 +286,20 @@ static int read_frame_internal( cli_pic_t *pic, y4m_hnd_t *h, int bit_depth_uc )
                 plane[j] = plane[j] << lshift;
         }
     }
-    return error;
+    return 0;
 }
 
 static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
 {
     y4m_hnd_t *h = handle;
 
-    if( i_frame > h->next_frame )
+    if( h->use_mmap )
+    {
+        pic->img.plane[0] = x264_cli_mmap( &h->mmap, h->frame_size * i_frame + h->seq_header_len, h->frame_size );
+        if( !pic->img.plane[0] )
+            return -1;
+    }
+    else if( i_frame > h->next_frame )
     {
         if( x264_is_regular_file( h->fh ) )
             fseek( h->fh, h->frame_size * i_frame + h->seq_header_len, SEEK_SET );
@@ -289,14 +319,39 @@ static int read_frame( cli_pic_t *pic, hnd_t handle, int i_frame )
     return 0;
 }
 
+static int release_frame( cli_pic_t *pic, hnd_t handle )
+{
+    y4m_hnd_t *h = handle;
+    if( h->use_mmap )
+        return x264_cli_munmap( &h->mmap, pic->img.plane[0] - h->frame_header_len, h->frame_size );
+    return 0;
+}
+
+static int picture_alloc( cli_pic_t *pic, hnd_t handle, int csp, int width, int height )
+{
+    y4m_hnd_t *h = handle;
+    return (h->use_mmap ? x264_cli_pic_init_noalloc : x264_cli_pic_alloc)( pic, csp, width, height );
+}
+
+static void picture_clean( cli_pic_t *pic, hnd_t handle )
+{
+    y4m_hnd_t *h = handle;
+    if( h->use_mmap )
+        memset( pic, 0, sizeof(cli_pic_t) );
+    else
+        x264_cli_pic_clean( pic );
+}
+
 static int close_file( hnd_t handle )
 {
     y4m_hnd_t *h = handle;
     if( !h || !h->fh )
         return 0;
+    if( h->use_mmap )
+        x264_cli_mmap_close( &h->mmap );
     fclose( h->fh );
     free( h );
     return 0;
 }
 
-const cli_input_t y4m_input = { open_file, x264_cli_pic_alloc, read_frame, NULL, x264_cli_pic_clean, close_file };
+const cli_input_t y4m_input = { open_file, picture_alloc, read_frame, release_frame, picture_clean, close_file };