avcodec: add unpack packed B-frames bitstream filter

Fixes Ticket #2913

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Changelog

@@ -13,6 +13,7 @@ version <next>:
 - Intel QSV-accelerated H.264 encoding
 - MMAL-accelerated H.264 decoding
 - basic APNG encoder and muxer
+- unpack DivX-style packed B-frames in MPEG-4 bitstream filter
 
 
 version 2.6:

doc/bitstream_filters.texi

@@ -139,6 +139,26 @@ ffmpeg -i frame_%d.jpg -c:v copy rotated.avi
 
 @section mp3_header_decompress
 
+@section mpeg4_unpack_bframes
+
+Unpack DivX-style packed B-frames.
+
+DivX-style packed B-frames are not valid MPEG-4 and were only a
+workaround for the broken Video for Windows subsystem.
+They use more space, can cause minor AV sync issues, require more
+CPU power to decode (unless the player has some decoded picture queue
+to compensate the 2,0,2,0 frame per packet style) and cause
+trouble if copied into a standard container like mp4 or mpeg-ps/ts,
+because MPEG-4 decoders may not be able to decode them, since they are
+not valid MPEG-4.
+
+For example to fix an AVI file containing an MPEG-4 stream with
+DivX-style packed B-frames using @command{ffmpeg}, you can use the command:
+
+@example
+ffmpeg -i INPUT.avi -codec copy -bsf:v mpeg4_unpack_bframes OUTPUT.avi
+@end example
+
 @section noise
 
 Damages the contents of packets without damaging the container. Can be

libavcodec/Makefile

@@ -841,6 +841,7 @@ OBJS-$(CONFIG_H264_MP4TOANNEXB_BSF)       += h264_mp4toannexb_bsf.o
 OBJS-$(CONFIG_IMX_DUMP_HEADER_BSF)        += imx_dump_header_bsf.o
 OBJS-$(CONFIG_MJPEG2JPEG_BSF)             += mjpeg2jpeg_bsf.o
 OBJS-$(CONFIG_MJPEGA_DUMP_HEADER_BSF)     += mjpega_dump_header_bsf.o
+OBJS-$(CONFIG_MPEG4_UNPACK_BFRAMES_BSF)   += mpeg4_unpack_bframes_bsf.o
 OBJS-$(CONFIG_MOV2TEXTSUB_BSF)            += movsub_bsf.o
 OBJS-$(CONFIG_MP3_HEADER_DECOMPRESS_BSF)  += mp3_header_decompress_bsf.o \
                                              mpegaudiodata.o

libavcodec/allcodecs.c

@@ -605,6 +605,7 @@ void avcodec_register_all(void)
     REGISTER_BSF(MJPEG2JPEG,            mjpeg2jpeg);
     REGISTER_BSF(MJPEGA_DUMP_HEADER,    mjpega_dump_header);
     REGISTER_BSF(MP3_HEADER_DECOMPRESS, mp3_header_decompress);
+    REGISTER_BSF(MPEG4_UNPACK_BFRAMES,  mpeg4_unpack_bframes);
     REGISTER_BSF(MOV2TEXTSUB,           mov2textsub);
     REGISTER_BSF(NOISE,                 noise);
     REGISTER_BSF(REMOVE_EXTRADATA,      remove_extradata);

libavcodec/mpeg4_unpack_bframes_bsf.c

@@ -0,0 +1,194 @@
+/*
+ * Bitstream filter for unpacking DivX-style packed B-frames in MPEG-4 (divx_packed)
+ * Copyright (c) 2015 Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
+ *
+ * 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 "avcodec.h"
+#include "mpeg4video.h"
+
+typedef struct UnpackBFramesBSFContext {
+    uint8_t *b_frame_buf;
+    int      b_frame_buf_size;
+    int      updated_extradata;
+} UnpackBFramesBSFContext;
+
+/* search next start code */
+static unsigned int find_startcode(const uint8_t *buf, int buf_size, int *pos)
+{
+    unsigned int startcode = 0xFF;
+
+    for (; *pos < buf_size;) {
+        startcode = ((startcode << 8) | buf[*pos]) & 0xFFFFFFFF;
+        *pos +=1;
+        if ((startcode & 0xFFFFFF00) != 0x100)
+            continue;  /* no startcode */
+        return startcode;
+    }
+
+    return 0;
+}
+
+/* determine the position of the packed marker in the userdata,
+ * the number of VOPs and the position of the second VOP */
+static void scan_buffer(const uint8_t *buf, int buf_size,
+                        int *pos_p, int *nb_vop, int *pos_vop2) {
+    unsigned int startcode;
+    int pos, i;
+
+    for (pos = 0; pos < buf_size;) {
+        startcode = find_startcode(buf, buf_size, &pos);
+
+        if (startcode == USER_DATA_STARTCODE && pos_p) {
+            /* check if the (DivX) userdata string ends with 'p' (packed) */
+            for (i = 0; i < 255 && pos + i + 1 < buf_size; i++) {
+                if (buf[pos + i] == 'p' && buf[pos + i + 1] == '\0') {
+                    *pos_p = pos + i;
+                    break;
+                }
+            }
+        } else if (startcode == VOP_STARTCODE && nb_vop) {
+            *nb_vop += 1;
+            if (*nb_vop == 2 && pos_vop2) {
+                *pos_vop2 = pos - 4; /* subtract 4 bytes startcode */
+            }
+        }
+    }
+}
+
+/* allocate new buffer and copy size bytes from src */
+static uint8_t *create_new_buffer(const uint8_t *src, int size) {
+    uint8_t *dst = av_malloc(size + FF_INPUT_BUFFER_PADDING_SIZE);
+
+    if (dst) {
+        memcpy(dst, src, size);
+        memset(dst + size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
+    }
+
+    return dst;
+}
+
+static int mpeg4_unpack_bframes_filter(AVBitStreamFilterContext *bsfc,
+                                       AVCodecContext *avctx, const char *args,
+                                       uint8_t  **poutbuf, int *poutbuf_size,
+                                       const uint8_t *buf, int      buf_size,
+                                       int keyframe)
+{
+    UnpackBFramesBSFContext *ctx = bsfc->priv_data;
+    int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
+
+    if (avctx->codec_id != AV_CODEC_ID_MPEG4) {
+        av_log(avctx, AV_LOG_ERROR,
+               "The mpeg4_unpack_bframes bitstream filter is only useful for mpeg4.\n");
+        return AVERROR(EINVAL);
+    }
+
+    if (!ctx->updated_extradata && avctx->extradata) {
+        int pos_p_ext = -1;
+        scan_buffer(avctx->extradata, avctx->extradata_size, &pos_p_ext, NULL, NULL);
+        if (pos_p_ext >= 0) {
+            av_log(avctx, AV_LOG_DEBUG,
+                   "Updating DivX userdata (remove trailing 'p') in extradata.\n");
+            avctx->extradata[pos_p_ext] = '\0';
+        }
+        ctx->updated_extradata = 1;
+    }
+
+    scan_buffer(buf, buf_size, &pos_p, &nb_vop, &pos_vop2);
+    av_log(avctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
+
+    if (pos_vop2 >= 0) {
+        if (ctx->b_frame_buf) {
+            av_log(avctx, AV_LOG_WARNING,
+                   "Missing one N-VOP packet, discarding one B-frame.\n");
+            av_freep(&ctx->b_frame_buf);
+            ctx->b_frame_buf_size = 0;
+        }
+        /* store the packed B-frame in the BSFContext */
+        ctx->b_frame_buf_size = buf_size - pos_vop2;
+        ctx->b_frame_buf      = create_new_buffer(buf + pos_vop2, ctx->b_frame_buf_size);
+        if (!ctx->b_frame_buf) {
+            ctx->b_frame_buf_size = 0;
+            return AVERROR(ENOMEM);
+        }
+    }
+
+    if (nb_vop > 2) {
+        av_log(avctx, AV_LOG_WARNING,
+       "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
+    }
+
+    if (nb_vop == 1 && ctx->b_frame_buf) {
+        /* use frame from BSFContext */
+        *poutbuf      = ctx->b_frame_buf;
+        *poutbuf_size = ctx->b_frame_buf_size;
+        /* the output buffer is distinct from the input buffer */
+        ret = 1;
+        if (buf_size <= MAX_NVOP_SIZE) {
+            /* N-VOP */
+            av_log(avctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
+            ctx->b_frame_buf      = NULL;
+            ctx->b_frame_buf_size = 0;
+        } else {
+            /* copy packet into BSFContext */
+            ctx->b_frame_buf_size = buf_size;
+            ctx->b_frame_buf      = create_new_buffer(buf , buf_size);
+            if (!ctx->b_frame_buf) {
+                ctx->b_frame_buf_size = 0;
+                av_freep(poutbuf);
+                *poutbuf_size = 0;
+                return AVERROR(ENOMEM);
+            }
+        }
+    } else if (nb_vop >= 2) {
+        /* use first frame of the packet */
+        *poutbuf      = (uint8_t *) buf;
+        *poutbuf_size = pos_vop2;
+    } else if (pos_p >= 0) {
+        av_log(avctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
+        *poutbuf_size = buf_size;
+        *poutbuf      = create_new_buffer(buf, buf_size);
+        if (!*poutbuf) {
+            *poutbuf_size = 0;
+            return AVERROR(ENOMEM);
+        }
+        /* remove 'p' (packed) from the end of the (DivX) userdata string */
+        (*poutbuf)[pos_p] = '\0';
+        /* the output buffer is distinct from the input buffer */
+        ret = 1;
+    } else {
+        /* copy packet */
+        *poutbuf      = (uint8_t *) buf;
+        *poutbuf_size = buf_size;
+    }
+
+    return ret;
+}
+
+static void mpeg4_unpack_bframes_close(AVBitStreamFilterContext *bsfc)
+{
+    UnpackBFramesBSFContext *ctx = bsfc->priv_data;
+    av_freep(&ctx->b_frame_buf);
+}
+
+AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
+    .name           = "mpeg4_unpack_bframes",
+    .priv_data_size = sizeof(UnpackBFramesBSFContext),
+    .filter         = mpeg4_unpack_bframes_filter,
+    .close          = mpeg4_unpack_bframes_close
+};

libavcodec/version.h

@@ -29,7 +29,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVCODEC_VERSION_MAJOR 56
-#define LIBAVCODEC_VERSION_MINOR  33
+#define LIBAVCODEC_VERSION_MINOR  34
 #define LIBAVCODEC_VERSION_MICRO 100
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \