lavc: add null codecs

They discard all input without ever returning any output. Useful for
development.

libavcodec/Makefile

@@ -219,6 +219,8 @@ OBJS-$(CONFIG_AMRWB_DECODER)           += amrwbdec.o celp_filters.o   \
                                           acelp_pitch_delay.o
 OBJS-$(CONFIG_AMV_ENCODER)             += mjpegenc.o mjpegenc_common.o
 OBJS-$(CONFIG_ANM_DECODER)             += anm.o
+OBJS-$(CONFIG_ANULL_DECODER)           += null.o
+OBJS-$(CONFIG_ANULL_ENCODER)           += null.o
 OBJS-$(CONFIG_ANSI_DECODER)            += ansi.o cga_data.o
 OBJS-$(CONFIG_APAC_DECODER)            += apac.o
 OBJS-$(CONFIG_APE_DECODER)             += apedec.o
@@ -747,6 +749,8 @@ OBJS-$(CONFIG_VCR1_DECODER)            += vcr1.o
 OBJS-$(CONFIG_VMDAUDIO_DECODER)        += vmdaudio.o
 OBJS-$(CONFIG_VMDVIDEO_DECODER)        += vmdvideo.o
 OBJS-$(CONFIG_VMNC_DECODER)            += vmnc.o
+OBJS-$(CONFIG_VNULL_DECODER)           += null.o
+OBJS-$(CONFIG_VNULL_ENCODER)           += null.o
 OBJS-$(CONFIG_VORBIS_DECODER)          += vorbisdec.o vorbisdsp.o vorbis.o \
                                           vorbis_data.o
 OBJS-$(CONFIG_VORBIS_ENCODER)          += vorbisenc.o vorbis.o \

libavcodec/allcodecs.c

@@ -884,6 +884,12 @@ extern const FFCodec ff_vp9_qsv_decoder;
 extern const FFCodec ff_vp9_vaapi_encoder;
 extern const FFCodec ff_vp9_qsv_encoder;
 
+// null codecs
+extern const FFCodec ff_vnull_decoder;
+extern const FFCodec ff_vnull_encoder;
+extern const FFCodec ff_anull_decoder;
+extern const FFCodec ff_anull_encoder;
+
 // The iterate API is not usable with ossfuzz due to the excessive size of binaries created
 #if CONFIG_OSSFUZZ
 const FFCodec * codec_list[] = {

libavcodec/codec_desc.c

@@ -3625,6 +3625,18 @@ static const AVCodecDescriptor codec_descriptors[] = {
         .long_name = NULL_IF_CONFIG_SMALL("AVFrame to AVPacket passthrough"),
         .props     = AV_CODEC_PROP_LOSSLESS,
     },
+    {
+        .id        = AV_CODEC_ID_VNULL,
+        .type      = AVMEDIA_TYPE_VIDEO,
+        .name      = "vnull",
+        .long_name = NULL_IF_CONFIG_SMALL("Null video codec"),
+    },
+    {
+        .id        = AV_CODEC_ID_ANULL,
+        .type      = AVMEDIA_TYPE_AUDIO,
+        .name      = "anull",
+        .long_name = NULL_IF_CONFIG_SMALL("Null audio codec"),
+    },
 };
 
 static int descriptor_compare(const void *key, const void *member)

libavcodec/codec_id.h

@@ -590,6 +590,16 @@ enum AVCodecID {
                                 * stream (only used by libavformat) */
     AV_CODEC_ID_FFMETADATA = 0x21000,   ///< Dummy codec for streams containing only metadata information.
     AV_CODEC_ID_WRAPPED_AVFRAME = 0x21001, ///< Passthrough codec, AVFrames wrapped in AVPacket
+    /**
+     * Dummy null video codec, useful mainly for development and debugging.
+     * Null encoder/decoder discard all input and never return any output.
+     */
+    AV_CODEC_ID_VNULL,
+    /**
+     * Dummy null audio codec, useful mainly for development and debugging.
+     * Null encoder/decoder discard all input and never return any output.
+     */
+    AV_CODEC_ID_ANULL,
 };
 
 /**

libavcodec/null.c

@@ -0,0 +1,97 @@
+/*
+ * Null codecs
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "config_components.h"
+
+#include "codec_internal.h"
+#include "decode.h"
+#include "encode.h"
+
+#if CONFIG_VNULL_DECODER || CONFIG_ANULL_DECODER
+static int null_decode(AVCodecContext *avctx, AVFrame *frame,
+                       int *got_frame, AVPacket *avpkt)
+{
+    *got_frame = 0;
+    return avpkt->size;
+}
+
+#if CONFIG_VNULL_DECODER
+const FFCodec ff_vnull_decoder = {
+    .p.name         = "vnull",
+    CODEC_LONG_NAME("null video"),
+    .p.type         = AVMEDIA_TYPE_VIDEO,
+    .p.id           = AV_CODEC_ID_VNULL,
+    .p.capabilities = AV_CODEC_CAP_DR1,
+    FF_CODEC_DECODE_CB(null_decode),
+};
+#endif
+
+#if CONFIG_ANULL_DECODER
+const FFCodec ff_anull_decoder = {
+    .p.name         = "anull",
+    CODEC_LONG_NAME("null audio"),
+    .p.type         = AVMEDIA_TYPE_AUDIO,
+    .p.id           = AV_CODEC_ID_ANULL,
+    .p.capabilities = AV_CODEC_CAP_DR1,
+    FF_CODEC_DECODE_CB(null_decode),
+};
+#endif
+
+#endif
+
+#if CONFIG_VNULL_ENCODER || CONFIG_ANULL_ENCODER
+static int null_encode(AVCodecContext *avctx, AVPacket *pkt,
+                       const AVFrame *frame, int *got_packet)
+{
+    *got_packet = 0;
+    return 0;
+}
+
+#if CONFIG_VNULL_ENCODER
+const FFCodec ff_vnull_encoder = {
+    .p.name         = "vnull",
+    CODEC_LONG_NAME("null video"),
+    .p.type         = AVMEDIA_TYPE_VIDEO,
+    .p.id           = AV_CODEC_ID_VNULL,
+    FF_CODEC_ENCODE_CB(null_encode),
+};
+#endif
+
+#if CONFIG_ANULL_ENCODER
+const FFCodec ff_anull_encoder = {
+    .p.name         = "anull",
+    CODEC_LONG_NAME("null audio"),
+    .p.type         = AVMEDIA_TYPE_AUDIO,
+    .p.id           = AV_CODEC_ID_ANULL,
+    .p.capabilities = AV_CODEC_CAP_VARIABLE_FRAME_SIZE,
+    .p.sample_fmts  = (const enum AVSampleFormat[]){
+        AV_SAMPLE_FMT_U8,  AV_SAMPLE_FMT_U8P,
+        AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_S16P,
+        AV_SAMPLE_FMT_S32, AV_SAMPLE_FMT_S32P,
+        AV_SAMPLE_FMT_S64, AV_SAMPLE_FMT_S64P,
+        AV_SAMPLE_FMT_FLT, AV_SAMPLE_FMT_FLTP,
+        AV_SAMPLE_FMT_DBL, AV_SAMPLE_FMT_DBLP,
+        AV_SAMPLE_FMT_NONE,
+    },
+    FF_CODEC_ENCODE_CB(null_encode),
+};
+#endif
+
+#endif