--- /dev/null
+// A shared library that you can LD_PRELOAD into an FFmpeg-using process
+// (most likely ffmpeg(1)) to make it output Metacube. This is obviously
+// pretty hacky, since it needs to override various FFmpeg functions,
+// so there are few guarantees here. It is written in C to avoid pulling
+// in the C++ runtime into FFmpeg's C-only world.
+//
+// You should not link to this library. It does not have ABI stability.
+// It is licensed the same as the rest of Cubemap.
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <dlfcn.h>
+#include <libavformat/avformat.h>
+#include <libavformat/avio.h>
+#include <libavutil/avassert.h>
+#include <libavutil/crc.h>
+#include <libavutil/error.h>
+#include <libavutil/intreadwrite.h>
+#include <limits.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/signal.h>
+#include "metacube2.h"
+
+static pthread_once_t metacube2_crc_once_control = PTHREAD_ONCE_INIT;
+static AVCRC metacube2_crc_table[257];
+
+// We need to store some extra information for each context,
+// so this is where we do it. The “opaque” field in the AVIOContext
+// points to this struct, but we can also look it up by the AVIOContext
+// pointer by scanning through the singly linked list starting with
+// first_extra_data.
+struct ContextExtraData {
+ struct ContextExtraData *next; // NULL for last entry.
+ AVIOContext *ctx; // The context we are associating data with.
+ bool seen_sync_point;
+ void *old_opaque;
+ int (*old_write_data_type)(void *opaque, uint8_t * buf,
+ int buf_size,
+ enum AVIODataMarkerType type,
+ int64_t time);
+
+ // Used during avformat_write_header(), to combine adjacent header blocks
+ // into one (in particular, the MP4 mux has an unneeded avio_flush()
+ // halfway throughout).
+ bool in_header;
+ int64_t header_first_time;
+ uint8_t *buffered_header;
+ size_t buffered_header_bytes;
+};
+static struct ContextExtraData *first_extra_data = NULL;
+
+// Look up ContextExtraData for the given context, creating a new one if needed.
+static struct ContextExtraData *get_extra_data(AVIOContext * ctx)
+{
+ for (struct ContextExtraData * ed = first_extra_data; ed != NULL;
+ ed = ed->next) {
+ if (ed->ctx == ctx) {
+ return ed;
+ }
+ }
+ struct ContextExtraData *ed = (struct ContextExtraData *)
+ malloc(sizeof(struct ContextExtraData));
+ ed->ctx = ctx;
+ ed->seen_sync_point = false;
+ ed->old_write_data_type = NULL;
+ ed->in_header = false;
+ ed->buffered_header = NULL;
+ ed->buffered_header_bytes = 0;
+
+ ed->next = first_extra_data;
+ first_extra_data = ed;
+ return ed;
+}
+
+// Clear ContextExtraData for a given context (presumably before it's freed).
+static void free_extra_data(AVIOContext * ctx)
+{
+ if (first_extra_data == NULL) {
+ return;
+ }
+ if (first_extra_data->ctx == ctx) {
+ struct ContextExtraData *to_free = first_extra_data;
+ first_extra_data = to_free->next;
+ free(to_free);
+ return;
+ }
+ for (struct ContextExtraData * ed = first_extra_data; ed != NULL;
+ ed = ed->next) {
+ if (ed->next != NULL && ed->next->ctx == ctx) {
+ struct ContextExtraData *to_free = ed->next;
+ ed->next = to_free->next;
+ free(to_free);
+ return;
+ }
+ }
+}
+
+static void metacube2_crc_init_table_once(void)
+{
+ av_assert0(av_crc_init
+ (metacube2_crc_table, 0, 16, 0x8fdb,
+ sizeof(metacube2_crc_table)) >= 0);
+}
+
+static uint16_t metacube2_compute_crc_ff(const struct
+ metacube2_block_header *hdr)
+{
+ static const int data_len = sizeof(hdr->size) + sizeof(hdr->flags);
+ const uint8_t *data = (uint8_t *) & hdr->size;
+ uint16_t crc;
+
+ pthread_once(&metacube2_crc_once_control,
+ metacube2_crc_init_table_once);
+
+ // Metacube2 specifies a CRC start of 0x1234, but its pycrc-derived CRC
+ // includes a finalization step that is done somewhat differently in av_crc().
+ // 0x1234 alone sent through that finalization becomes 0x394a, and then we
+ // need a byte-swap of the CRC value (both on input and output) to account for
+ // differing conventions.
+ crc = av_crc(metacube2_crc_table, 0x4a39, data, data_len);
+ return av_bswap16(crc);
+}
+
+static int write_packet(void *opaque, uint8_t * buf, int buf_size,
+ enum AVIODataMarkerType type, int64_t time)
+{
+ if (buf_size < 0) {
+ return AVERROR(EINVAL);
+ }
+
+ struct ContextExtraData *ed = (struct ContextExtraData *) opaque;
+
+ if (ed->in_header) {
+ if (ed->buffered_header_bytes == 0) {
+ ed->header_first_time = time;
+ }
+
+ size_t new_buffered_header_bytes =
+ ed->buffered_header_bytes + buf_size;
+ if (new_buffered_header_bytes < ed->buffered_header_bytes) {
+ return AVERROR(ENOMEM);
+ }
+ ed->buffered_header =
+ (uint8_t *) realloc(ed->buffered_header,
+ new_buffered_header_bytes);
+ if (ed->buffered_header == NULL) {
+ return AVERROR(ENOMEM);
+ }
+
+ memcpy(ed->buffered_header + ed->buffered_header_bytes,
+ buf, buf_size);
+ ed->buffered_header_bytes = new_buffered_header_bytes;
+ return buf_size;
+ }
+ // Find block size if we add a Metacube2 header in front.
+ unsigned new_buf_size =
+ (unsigned) buf_size + sizeof(struct metacube2_block_header);
+ if (new_buf_size < (unsigned) buf_size
+ || new_buf_size > (unsigned) INT_MAX) {
+ // Overflow.
+ return -1;
+ }
+ // Fill in the header.
+ struct metacube2_block_header hdr;
+ int flags = 0;
+ if (type == AVIO_DATA_MARKER_SYNC_POINT)
+ ed->seen_sync_point = 1;
+ else if (type == AVIO_DATA_MARKER_HEADER)
+ // NOTE: If there are multiple blocks marked METACUBE_FLAGS_HEADER,
+ // only the last one will count. This may become a problem if the
+ // mux flushes halfway through the stream header; if so, we would
+ // need to keep track of and concatenate the different parts.
+ flags |= METACUBE_FLAGS_HEADER;
+ else if (ed->seen_sync_point)
+ flags |= METACUBE_FLAGS_NOT_SUITABLE_FOR_STREAM_START;
+
+ memcpy(hdr.sync, METACUBE2_SYNC, sizeof(hdr.sync));
+ AV_WB32(&hdr.size, buf_size);
+ AV_WB16(&hdr.flags, flags);
+ AV_WB16(&hdr.csum, metacube2_compute_crc_ff(&hdr));
+
+ int ret;
+ ed->ctx->opaque = ed->old_opaque;
+ if (new_buf_size < ed->ctx->max_packet_size) {
+ // Combine the two packets. (This is what we normally want.)
+ // So we allocate a new block, with a Metacube2 header in front.
+ uint8_t *buf_with_hdr = (uint8_t *) malloc(new_buf_size);
+ if (buf_with_hdr == NULL) {
+ return AVERROR(ENOMEM);
+ }
+ memcpy(buf_with_hdr, &hdr, sizeof(hdr));
+ memcpy(buf_with_hdr + sizeof(hdr), buf, buf_size);
+ if (ed->old_write_data_type) {
+ ret =
+ ed->old_write_data_type(ed->old_opaque,
+ buf_with_hdr,
+ new_buf_size, type,
+ time);
+ } else {
+ ret =
+ ed->ctx->write_packet(ed->old_opaque,
+ buf_with_hdr,
+ new_buf_size);
+ }
+ free(buf_with_hdr);
+
+ if (ret >= 0
+ && ret >= sizeof(struct metacube2_block_header)) {
+ ret -= sizeof(struct metacube2_block_header);
+ }
+ } else {
+ // Send separately. This will split a header block if it's really large,
+ // which we don't want, but that's how things are.
+ if (ed->old_write_data_type) {
+ ret =
+ ed->old_write_data_type(ed->old_opaque,
+ (uint8_t *) & hdr,
+ sizeof(hdr), type,
+ time);
+ } else {
+ ret =
+ ed->ctx->write_packet(ed->old_opaque,
+ (uint8_t *) & hdr,
+ sizeof(hdr));
+ }
+ if (ret < 0) {
+ return ret;
+ }
+ if (ret != sizeof(hdr)) {
+ return AVERROR(EIO);
+ }
+
+ if (ed->old_write_data_type) {
+ ret =
+ ed->old_write_data_type(ed->old_opaque, buf,
+ buf_size, type, time);
+ } else {
+ ret =
+ ed->ctx->write_packet(ed->old_opaque, buf,
+ buf_size);
+ }
+ }
+
+ ed->ctx->opaque = ed;
+ return ret;
+}
+
+// Actual hooked functions below.
+
+int avformat_write_header(AVFormatContext * ctx, AVDictionary ** options)
+{
+ metacube2_crc_init_table_once();
+
+ struct ContextExtraData *ed = get_extra_data(ctx->pb);
+ ed->old_opaque = ctx->pb->opaque;
+ ed->old_write_data_type = ctx->pb->write_data_type;
+ ctx->pb->opaque = ed;
+ ctx->pb->write_data_type = write_packet;
+ ctx->pb->seek = NULL;
+ ctx->pb->seekable = 0;
+ if (ed->old_write_data_type == NULL) {
+ ctx->pb->ignore_boundary_point = 1;
+ }
+
+ int (*original_func)(AVFormatContext * ctx,
+ AVDictionary ** options);
+ original_func = dlsym(RTLD_NEXT, "avformat_write_header");
+
+ ed->in_header = true;
+ int ret = (*original_func) (ctx, options);
+ ed->in_header = false;
+
+ if (ed->buffered_header_bytes > 0) {
+ int hdr_ret = write_packet(ed, ed->buffered_header,
+ ed->buffered_header_bytes,
+ AVIO_DATA_MARKER_HEADER,
+ ed->header_first_time);
+ free(ed->buffered_header);
+ ed->buffered_header = NULL;
+
+ if (hdr_ret >= 0 && hdr_ret < ed->buffered_header_bytes) {
+ hdr_ret = AVERROR(EIO);
+ }
+ ed->buffered_header_bytes = 0;
+ if (hdr_ret < 0) {
+ return hdr_ret;
+ }
+ }
+
+ return ret;
+}
+
+void avformat_free_context(AVFormatContext * ctx)
+{
+ if (ctx == NULL) {
+ return;
+ }
+ free_extra_data(ctx->pb);
+
+ void (*original_func)(AVFormatContext * ctx);
+ original_func = dlsym(RTLD_NEXT, "avformat_free_context");
+ return (*original_func) (ctx);
+}
+
+// Hook so that we can restore opaque instead of ours being freed by the caller.
+int avio_close(AVIOContext * ctx)
+{
+ if (ctx == NULL) {
+ return 0;
+ }
+ struct ContextExtraData ed = *get_extra_data(ctx);
+ free_extra_data(ctx);
+ ctx->opaque = ed.old_opaque;
+
+ int (*original_func)(AVIOContext * ctx);
+ original_func = dlsym(RTLD_NEXT, "avio_close");
+ return (*original_func) (ctx);
+}
+
+// Identical to FFmpeg's definition, but we cannot hook avio_close()
+// when called from FFmpeg's avio_closep(), so we need to hook this one
+// as well.
+int avio_closep(AVIOContext ** s)
+{
+ int ret = avio_close(*s);
+ *s = NULL;
+ return ret;
+}
+
+
+int avio_open2(AVIOContext ** s, const char *filename, int flags,
+ const AVIOInterruptCB * int_cb, AVDictionary ** options)
+{
+ // The options, if any, are destroyed on entry, so we can add new ones
+ // pretty freely.
+ if (options && *options) {
+ AVDictionaryEntry *listen =
+ av_dict_get(*options, "listen", NULL,
+ AV_DICT_MATCH_CASE);
+ if (listen != NULL && atoi(listen->value) != 0) {
+ // If -listen is set, we'll want to add a header, too.
+ av_dict_set(options, "headers",
+ "Content-encoding: metacube\r\n",
+ AV_DICT_APPEND);
+ }
+ }
+
+ int (*original_func)(AVIOContext ** s, const char *filename,
+ int flags, const AVIOInterruptCB * int_cb,
+ AVDictionary ** options);
+ original_func = dlsym(RTLD_NEXT, "avio_open2");
+ return (*original_func) (s, filename, flags, int_cb, options);
+}
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